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Step 1 Sample Test Answers + Explanations 2026
USMLE STEP 1 Free 120 Explanations
Updated May 2026
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Updated as of May 2026
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You can download the Free 120 STEP 1 Sample Test Questions on the USMLE website here. The order of answers and explanations here is based on the online NBME platform (not the pdf) as of May 2026.
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Table of Contents
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Block 1
Question 1:
The correct answer is A. This 53-year-old woman presents with a 6-year history of hand stiffness and pain, accompanied by joint deformities as shown in the image, which is consistent with rheumatoid arthritis (RA). Testing for anti-citrullinated peptide antibodies (ACPA) is the most specific diagnostic marker for RA.
Rheumatoid arthritis is a chronic autoimmune disease that primarily affects the small joints of the hands and feet. It is characterized by:
- Symmetrical joint pain and stiffness: Especially in the morning, lasting more than 30 minutes.
- Joint deformities: including ulnar deviation, swan-neck deformities, and boutonnière deformities.
- Systemic features: Fatigue and other inflammatory symptoms are common in RA.
Anti-citrullinated peptide antibodies (ACPA), such as anti-cyclic citrullinated peptide (anti-CCP) antibodies, are highly specific for RA and are detected in most patients with the disease. They are associated with more severe disease and are helpful in confirming the diagnosis.
Incorrect answers:
B. This test is used to diagnose primary biliary cholangitis, a liver disease, and is not relevant to joint pain or deformities.
C. HLA-DQ2 is associated with celiac disease, which can present with gastrointestinal symptoms and malabsorption, not joint deformities.
D. Abnormalities in erythroid precursors are associated with hematologic conditions such as anemias, not RA.
E. Abnormalities in thrombopoietic precursors are linked to platelet disorders, which are unrelated to RA.
Question 2:
The correct answer is B. Asymmetric smile. This 80-year-old patient has a pontine infarction, as indicated by the shaded area involving the left ventromedial and ventrolateral caudal pons. The lesion damages the left corticospinal tract and medial lemniscus, leading to contralateral (right-sided) hemiparesis and loss of vibration/two-point discrimination. Simultaneously, it involves the exiting fibers of the abducens nerve (CN VI), preventing left eye abduction, and the facial nerve (CN VII) fascicles, which leads to an ipsilateral peripheral facial palsy presenting as an asymmetric smile. For USMLE, a cross-section of the caudal pons showing a ventromedial/lateral lesion paired with alternating hemiparesis and cranial nerve VI/VII deficits is the classic presentation of a pontine branch stroke of the basilar artery.
Incorrect answers:
A. Anesthesia of the left side of the face would require involvement of the principal sensory nucleus of CN V (mid-pons) or the spinal trigeminal nucleus and tract (lateral pons/medulla). The shaded lesion spares these dorsolateral structures.
C. Hoarseness is caused by a lesion to the nucleus ambiguus or the fibers of CN X (Vagus nerve). These structures are located exclusively in the medulla (e.g., Wallenberg syndrome) rather than the pons.
D. Loss of accommodation is mediated by the Edinger-Westphal nucleus and the oculomotor nerve (CN III). This reflex pathway is localized entirely within the midbrain, which is superior to this pontine lesion.
E. Paralysis of the tongue is caused by a lesion to the hypoglossal nucleus or exiting fibers of CN XII. This nucleus is located medially within the medulla (e.g., medial medullary syndrome) and is not affected by a caudal pontine stroke.
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Question 3:
The correct answer is B. This patient’s findings, including shortness of breath, tachycardia, tachypnea, and deep vein thrombosis (DVT) in the right calf, are consistent with a pulmonary embolism (PE). Risk factors such as long flights and a predisposition to thrombosis (due to genetic factors or medications) are significant. Factor V Leiden mutation is associated with an inability to break down factor V, which leads to thrombosis. Factor V Leiden mutation is the most common cause of hereditary thrombophilia.
Incorrect answers:
A. While antithrombin III deficiency increases the risk of thrombosis, it is usually asymptomatic and far less common than Factor V Leiden. Additionally, higher doses of heparin are needed to produce an effect in patients with antithrombin III deficiency.
C. Hemophilia would result in bleeding, not thrombosis, and is not associated with the clinical presentation described.
D. Protein C deficiency is much less common than Factor V Leiden and would also be associated with a higher risk of thrombosis, but it is not the most likely cause in this case. Usually it occurs in the first few days of warfarin use but this patient has no such history of drug use.
E. Von Willebrand disease is a bleeding disorder and would not cause thrombosis.
Question 4:
The correct answer is C. This patient presents with a 2-week history of fever, throat pain, bilateral tonsillar exudate, and generalized lymphadenopathy, which are consistent with mononucleosis-like symptoms. The negative heterophile antibody test rules out Epstein-Barr virus infection (Choice A). Given the presence of anemia, thrombocytopenia, and leukopenia, HIV is the most likely diagnosis. For USMLE, mononucleosis-like symptoms, suspect EBV, CMV, Toxoplasmosis and HIV.
Incorrect answers:
A. Epstein-Barr virus infection is ruled out by the negative heterophile antibody (Monospot) test.
B. Gonococcal pharyngitis is associated with fever, tonsillar exudate, and localized lymphadenitis, but it does not typically cause generalized lymphadenopathy or the laboratory abnormalities seen in this patient.
D. Lymphogranuloma venereum infection is usually associated with a painless genital ulcer and painful inguinal lymphadenopathy, not the generalized lymphadenopathy or throat symptoms seen here.
E. Streptococcal pharyngitis typically presents with fever, sore throat with exudates, and localized cervical lymphadenopathy. It is an acute infection, unlike this patient’s subacute presentation.
Question 5:
The correct answer is C. This 60-year-old woman presents with fever, rash, acute kidney injury (AKI), and eosinophilia following 21 days of intravenous oxacillin for Staphylococcus aureus endocarditis. Urine microscopy shows eosinophils and white blood cell (WBC) casts, which are highly suggestive of acute interstitial nephritis (AIN). AIN is a hypersensitivity reaction typically caused by medications, including beta-lactam antibiotics like oxacillin.
Incorrect answers:
A. Collapsing FSGS is associated with conditions like HIV infection, heroin use, or certain medications. It manifests with nephrotic syndrome (severe proteinuria, hypoalbuminemia, and edema) rather than AKI with eosinophiluria and WBC casts.
B. This is characteristic of crescentic glomerulonephritis, a rapidly progressive glomerulonephritis (RPGN) associated with autoimmune diseases like ANCA-associated vasculitis or Goodpasture syndrome. These diseases usually cause nephritic syndrome (hematuria, RBC casts, and hypertension), which is not seen here.
D. This finding is associated with diabetic nephropathy, which develops over years and manifests with proteinuria, not AKI. This patient has no history of diabetes and lacks findings consistent with chronic diabetic nephropathy.
E. This is seen in acute tubular necrosis (ATN), which occurs due to ischemia or nephrotoxins (e.g., aminoglycosides, contrast dye). While ATN may cause AKI, it does not cause eosinophilia, WBC casts, or fever.
Question 6:
The correct answer is D. This patient has symptomatic syringomyelia, as evidenced by the gradual progression of upper extremity weakness and decreased pain sensation. MRI confirms the diagnosis by showing a central syrinx in the cervical spine. A history of trauma increases the risk of syrinx formation. Fine touch and vibratory sense are spared in syringomyelia, except in advanced disease.
Incorrect answers:
A. A strict vegan diet may lead to vitamin B12 deficiency. vitamin B12 deficiency causes subacute combined degeneration which can present as sensory, motor and balance deficits that are distributed all over the body not only limited to the upper extremities.
B. A family history could increase the risk of certain conditions like Rheumatoid arthritis and osteoarthritis.
C. Recent travel increases the risk of deep vein thrombosis (DVT), which typically presents with unilateral leg swelling, pain, and erythema rather than the neurological deficits seen in this patient.
E. Unintended weight loss is commonly associated with malignancies. This patient’s history and MRI findings suggest post-traumatic syringomyelia rather than a neoplastic process.
Question 7:
The correct answer is E. Vascular obstruction by lipid-rich plaques. This 68-year-old patient presents with classic symptoms of peripheral artery disease (PAD), characterized by intermittent claudication (lower extremity pain and cramping induced by walking and relieved by rest). His physical exam demonstrates chronic ischemic changes, including atrophic skin, hair loss, cool extremities, and absent distal pulses (posterior tibial and dorsalis pedis). The fundamental pathophysiological mechanism underlying PAD is atherosclerosis, which involves the progressive narrowing of large and medium-sized arteries due to vascular obstruction by lipid-rich plaques.
Management of symptomatic PAD focuses on cardiovascular risk reduction and symptom relief. Initial treatments include supervised exercise therapy, aggressive risk factor modification with high-intensity statins and blood pressure control, and antiplatelet therapy (e.g., aspirin or clopidogrel) to prevent major adverse cardiovascular events. For patients with persistent claudication despite exercise therapy, a phosphodiesterase inhibitor like cilostazol can be added to improve walking distance.
Incorrect answers:
A. Fibromuscular dysplasia is a non-atherosclerotic, non-inflammatory vascular disease that typically affects young women and primarily involves the renal and internal carotid arteries, leading to secondary hypertension or stroke rather than lower extremity claudication.
B. Giant cell arteritis is a large-vessel vasculitis that typically affects patients older than 50, but classic symptoms involve the branches of the carotid artery, presenting as temporal headaches, jaw claudication, and amaurosis fugax, rather than lower extremity ischemia.
C. Hyaline arteriosclerosis is a disease of small arterioles characteristically seen in long-standing hypertension and diabetes mellitus. While this patient has both risk factors and underlying nephropathy due to arteriolosclerosis, it affects microvasculature rather than the large/medium conduit arteries responsible for lower limb claudication and absent pedal pulses.
D. Segmental inflammation of medium-sized vessels describes Polyarteritis nodosa (PAN) or Thromboangiitis obliterans (Buerger disease). PAN presents with systemic symptoms (fever, weight loss) and renal/gastrointestinal ischemia, while Buerger disease causes digital ischemia and gangrene strictly in young, heavy smokers, which does not align with this patient’s presentation.
Question 8:
The correct answer is D. Fused commissures. This 31-year-old woman presents with progressive shortness of breath, fatigue, and pulmonary congestion (crackles, dullness to percussion) after emigrating from Nigeria. She has a critical history of a hospital admission for a febrile illness and a heart condition at age 10. This clinical presentation is highly characteristic of chronic rheumatic heart disease affecting the mitral valve, leading to severe mitral stenosis.
Chronic rheumatic carditis develops years after an initial episode of acute rheumatic fever (caused by untreated Streptococcus pyogenes pharyngitis). Recurrent, subclinical immune-mediated inflammation leads to progressive fibrotic thickening, calcification, and fused commissures of the valve leaflets, often accompanied by fusion and shortening of the chordae tendineae. This creates a rigid, narrowed valve orifice (classic fish-mouth deformity) that restricts blood flow from the left atrium to the left ventricle during diastole, causing elevated left atrial pressure that backs up into the pulmonary circulation.
Cardiac Auscultation Findings: On physical examination, this condition is characterized by a unique triad of findings:
- Loud first heart sound (S1): Caused by the stiff, fibrotic mitral leaflets snapping shut under increased left atrial pressure at the start of systole.
- Opening snap (OS): A high-pitched sound heard early in diastole, caused by the sudden, forceful opening of the stenotic and rigid mitral valve.
- Mid-diastolic rumble: A low-pitched rumbling murmur with presystolic accentuation, best heard at the cardiac apex using the bell of the stethoscope with the patient in the left lateral decubitus position.
Incorrect answers:
A & E. Ballooned leaflets and myxomatous degeneration are the pathologic hallmarks of mitral valve prolapse (MVP). This is a benign connective tissue disorder where the leaflets become redundant and floppy, bowing into the left atrium during systole, which produces a mid-systolic click and a late systolic murmur.
B. Bulky cusp vegetations characterize active infective endocarditis. These are friable masses composed of platelets, fibrin, and microorganisms that destroy the valve leaflets, presenting with acute systemic symptoms like high fever, new murmurs, and embolic phenomena.
C. Calcified nodules are characteristic of age-related degenerative (senile) calcific aortic stenosis. This is a wear-and-tear disease that typically presents in patients older than 65 years with a harsh systolic crescendo-decrescendo murmur, not a diastolic issue in a young woman.
Question 9:
The correct answer is A. In motivational interviewing, the physician should acknowledge the patient’s resistance to change and guide them toward motivation for that change. Motivational interviewing must always be patient-centered, so open-ended questions encouraging patients to reflect on the benefits of change are particularly effective; they also help explore the patient’s intrinsic motivations for quitting. Through this approach, the patient can consider both the advantages and risks of making a change, thereby increasing their readiness to act.
Incorrect answers:
B & D. While these statements may be true, motivational interviewing is centered around the patient. These options emphasize the physician’s perspective instead of fostering the patient’s self-motivation.
C & D. These statements blame the patient and may create guilt, which can be counterproductive and harm the patient-physician relationship.
Question 10:
The correct answer is B. Caloric insufficiency. This 18-month-old girl presents with nonorganic failure to thrive due to inadequate nutritional intake. Her length tracks along the 25th percentile, while her weight has fallen below the 5th percentile. Pathophysiologically, when calories are insufficient, the body prioritizes linear bone growth and brain development over adipose tissue accumulation, causing weight to drop first while length is initially preserved.
Management focuses on dietary optimization, such as scheduling structured meals, increasing caloric density, and limiting excessive milk intake (which blunts appetite for solids). Routine lab tests are not indicated unless nutritional counseling fails.
Incorrect answers:
A. Adrenal insufficiency presents with systemic symptoms like vomiting, diarrhea, lethargy, skin hyperpigmentation, or electrolyte abnormalities, which are absent in this healthy child.
C. Constitutional growth delay features a parallel drop in both weight and length percentiles within the first 2 years of life before stabilizing, accompanied by a delayed bone age.
D. Familial short stature presents with both length and weight tracking consistently along a lower percentile from early infancy, matching the short stature of the parents.
E. Growth hormone deficiency primarily impairs linear skeletal growth, causing a progressive decline in the length percentile while weight is relatively preserved.
Question 11:
The correct answer is A. Internal validity. This prospective cohort study evaluates the relationship between dietary calcium and osteoporosis risk. Adding a missing major calcium source (yogurt) to the questionnaire prevents misclassification bias. Accurately capturing total exposure ensures the study measures what it truly intends to measure, maximizing internal validity.
Internal validity represents the degree to which the observed clinical findings truly reflect the cause-and-effect relationship within the study sample, free from systematic design or measurement flaws.
Incorrect answers:
B. Inter-rater reliability measures the consistency between different observers recording the same data point, which is unaffected by modifying a self-administered questionnaire.
C. Response rate is the percentage of invited individuals who complete the study; adding items does not increase participation and can lower it if the survey becomes too long.
D. Type I error (alpha) is the probability of finding a false positive result, which is managed by adjusting the statistical significance threshold (typically $0.05$) rather than changing questionnaire variables.
Question 12:
The correct answer is D. Reduviid bug. This 40-year-old asymptomatic woman from El Salvador has Chagas disease (Trypanosoma cruzi), which is endemic to Central and South America and classically transmitted by the Reduviid (kissing) bug. The insect feeds at night and defecates near the wound; the host then scratches the infectious feces into the bite site or mucous membranes.
While initially asymptomatic, chronic untreated infection can cause severe long-term complications, including dilated cardiomyopathy, apical aneurysms, megacolon, and megaesophagus.
Incorrect answers:
A. Bedbugs cause localized, pruritic skin wheals but do not transmit systemic pathogens like Trypanosoma cruzi.
B. Black flies transmit Onchocerca volvulus, the tissue nematode responsible for causing river blindness (onchocerciasis).
C. Mosquitos serve as vectors for entirely different diseases, including malaria (Anopheles), dengue, and yellow fever (Aedes)
E. Ticks transmit bacterial and protozoal illnesses such as Lyme disease, Rocky Mountain spotted fever, and babesiosis.
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Question 13:
The correct answer is A. “Help me to understand what you are hoping I can do for you today.” This 40-year-old man with irritable bowel syndrome (IBS) frequently seeks care but continuously refuses conventional treatment, preferring his grandmother’s herbal tea. When handling chronic nonadherence in patients who still actively seek medical encounters, the most appropriate initial strategy is to use open-ended, nonjudgmental questioning to explore their expectations and goals for the visit. This fosters collaboration and uncovers hidden agendas or specific fears.
Ethically, addressing patient autonomy requires exploring the underlying reasons for treatment refusal rather than forcing compliance or prematurely ending the therapeutic relationship.
Incorrect answers:
B. Prescribing medication while demanding the patient reconsider is overly directive, which increases resistance and damages rapport when dealing with chronic nonadherence.
C. Asking why the patient keeps coming back carries a dismissive, adversarial tone that invalidates their distress and can cause complete disengagement from healthcare.
D. Focusing immediately on the herbal tea narrows the discussion too quickly to a specific alternative therapy instead of addressing the broader issue of the patient’s expectations.
E. Stating there is nothing that can be done if medication is refused represents a premature abandonment of the patient, failing to recognize that supportive care, validation, and reassurance provide clinical value.
Question 14:
The correct answer is B. alpha 1 Adrenergic antagonism. This 72-year-old man presents with typical lower urinary tract symptoms (LUTS)—including increased urinary frequency, nocturia, and a slow urinary stream—secondary to benign prostatic hyperplasia (BPH), confirmed by a diffusely enlarged, symmetric prostate on digital rectal examination. First-line medical therapy for rapid symptom relief features alpha 1 adrenergic antagonists (e.g., tamsulosin, doxazosin). These agents block alpha 1 receptors located heavily on the smooth muscle of the prostatic urethra and bladder neck, causing smooth muscle relaxation, decreasing dynamic outflow resistance, and significantly improving urine flow.
Alternative long-term treatment includes 5-alpha reductase inhibitors (e.g., finasteride), which block the conversion of testosterone to dihydrotestosterone (DHT) to reduce overall prostate volume, but require months to become clinically effective.
Incorrect answers:
A. alpha 1 Adrenergic agonism (e.g., phenylephrine, midodrine) induces smooth muscle contraction at the bladder neck, which would worsen urinary obstruction and potentially precipitate acute urinary retention in a patient with BPH.
C. alpha 2 Adrenergic agonism (e.g., clonidine, methyldopa) acts centrally to decrease sympathetic outflow, primarily used as a centrally acting antihypertensive agent rather than a treatment for localized urinary tract symptoms.
D. alpha 2 Adrenergic antagonism historically found use in managing erectile dysfunction by increasing central sympathetic activity, but it plays no role in relaxing prostatic smooth muscle.
E. beta 1 Adrenergic agonism (e.g., dobutamine) exerts positive inotropic and chronotropic effects on the myocardium to manage cardiogenic shock or acute heart failure, carrying no physiological effect on prostatic tissue.
F. beta 1 Adrenergic antagonism (e.g., metoprolol, atenolol) involves beta-blockers utilized for hypertension, ischemic heart disease, and rate control in tachyarrhythmias, without any specific clinical utility in treating BPH.
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Question 15:
The correct answer is A. This patient has manic symptoms with psychotic features as described in this scenario. Manic symptoms include rapid speech, loose associations, and lack of sleep. Psychotic features include hallucinations (hearing voices) and delusions (married to the president’s twin brother, receiving instructions from a higher being). it’s differentiated from Schizoaffective disorder as the latter is characterized by psychotic symptoms at least 2 weeks with the absence of Mood disorder.
Incorrect answers:
B. Brief psychotic disorder involves psychotic symptoms lasting less than 30 days. This patient’s symptoms have persisted for more than 2 months, in addition to manic episodes, ruling out this diagnosis.
C. Delusional disorder is characterized by fixed, false beliefs, but the patient usually functions well otherwise. This patient displays marked impairment and manic features, which exclude this diagnosis.
D. Psychotic disorder due to a general medical condition requires evidence of an underlying medical condition causing the symptoms. No information in this scenario supports such a diagnosis.
E. Schizophrenia requires symptoms (e.g., hallucinations, delusions, disorganized speech) to persist for >6 months. Additionally, the presence of manic symptoms strongly supports a different diagnosis.
Question 16:
The correct answer is B. Cimetidine: B, Omeprazole: A. Both drugs are acid-suppressants that increase gastric pH over time. Omeprazole is a proton pump inhibitor (PPI) that irreversibly binds the H/K ATPase pump, providing profound, long-lasting acid suppression (Curve A). Cimetidine is an H2 receptor antagonist; it blocks histamine-mediated acid secretion but leaves gastrin and acetylcholine pathways partially active, resulting in a more modest, lower peak in pH (Curve B).
Because PPIs completely shut down the final common pathway of acid production, they cause a significantly greater and more sustained rise in gastric pH than H2 blockers.
Incorrect answers:
Curves C & D. These curves show a decrease in pH over time (increased acidity), which represents the physiological response to an acid stimulant (like histamine or gastrin) rather than an acid suppressant.
Options C, D, E, & F. These options incorrectly pair Cimetidine or Omeprazole with acid-inducing curves (C or D), or invert their relative potencies by suggesting Cimetidine elevates pH higher than Omeprazole.
Question 17:
The correct answer is B. This patient has new metastatic lesions in the liver and lungs. Metastatic spread from the right side of the colon follows this pathway: the superior mesenteric vein drains blood from the right colon into the portal vein, which then enters the liver. From the liver, cancer cells can spread through the hepatic veins, into the inferior vena cava (IVC), and subsequently to the heart (right atrium and right ventricle) and pulmonary vasculature, leading to metastasis in the lungs.
Incorrect answers:
A & C. These veins drain the left side of the colon, NOT the right.
D. The middle colic artery supplies part of the transverse colon and does not contribute to venous drainage or cancer spread.
E. The pulmonary veins carry oxygenated blood from the lungs to the left atrium and are not involved in the metastatic process.
F. Arteries do not play a primary role in the venous spread of metastases.
G. The superior vena cava drains blood from the upper body (head, neck, and upper extremities) and does not play a role in this metastatic process.
Question 18:
The correct answer is E. Scabies. This 4-year-old boy has a classic presentation of scabies, an infestation caused by the mite Sarcoptes scabiei. The hallmark finding is severe pruritus (worse at night) along with short, thin, elevated serpiginous tracks (burrows). The lesions characteristically favor the interdigital web spaces of the hands, axillae, waistline, and inner thighs, with small vesicles marking where the female mite resides.
Incorrect answers:
A. Chickenpox presents with fever and a generalized rash of pruriginous vesicles at different stages of healing (“dewdrops on a rose petal”), not linear tracks.
B. Ehrlichiosis is a tick-borne illness causing systemic symptoms (fever, myalgias) and leukopenia; a rash is rare and never forms burrows.
C. Lyme disease is characterized by erythema migrans, an expanding red rash with central clearing (“bull’s-eye” appearance) at a tick bite site.
D. Pediculosis (lice) involves hair or clothing infestation with intense itching and visible nits (eggs), but does not cause intraepidermal burrows.
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Question 19:
The correct answer is E. This patient with sickle cell disease (SCD) likely has gallstones due to chronic hemolysis, which increases unconjugated bilirubin levels. When bilirubin levels exceed the bile’s solubility capacity, bilirubin stones form a common complication of chronic hemolytic anemias, including SCD. in SCD, patients with functional asplenia are at higher risk for infections against encapsulated organisms. and complications like gallstones.
Incorrect answers:
B. Decreased bile salt reabsorption occurs in malabsorption syndromes (e.g., Crohn’s disease, ileal resection), leading to cholesterol stone formation due to impaired micelle formation, but this is not the mechanism in SCD.
C. Increased cholesterol-to-bile ratio is common in cholesterol stone formation, typically seen in middle-aged, obese, fertile women due to estrogen’s effect on cholesterol metabolism. This does not explain gallstones in an SCD patient.
A & D. These options do not contribute significantly to gallstone formation in this patient’s case.
Question 20:
The correct answer is D. This patient most likely has MEN2A syndrome, which is suggested by the presence of pheochromocytoma and a neck mass likely originating from parafollicular cells, most likely thyroid carcinoma. Additionally, the family history of the disease further supports the diagnosis. MEN2A is associated with mutations in the RET proto-oncogene. MEN2A is associated Thyroid carcinoma, Parathyroid hyperplasia, Pheochromocytoma (TPP)
Incorrect answers:
A. Cell cycle regulation genes include TP53, RB, Cyclins, CDKs. RET oncogene is unrelated.
B. DNA mismatch repair genes include MLH1, MSH2. They are involved in Hereditary non polyposis colorectal cancers. RET oncogene is unrelated
C. Metastasis suppressor genes generally inhibit spread of tumors. RET oncogene in unrelated
E. Tumor suppressor genes include TP53, RB. RET oncogene is unrelated
Block 2
Question 21:
The correct answer is A. This 6-year-old girl presents with vaginal bleeding, breast development, and pubic hair growth, which are signs of precocious puberty. Laboratory findings reveal elevated estradiol and gonadotropins (FSH and LH), particularly a high LH level in response to endogenous stimulation. This pattern suggests activation of the hypothalamic-pituitary-gonadal axis, also known as central precocious puberty. Central activation occurs due to the early maturation of gonadotropin-releasing hormone (GnRH)-secreting neurons in the hypothalamus.
Incorrect answers:
B. Prolactin secretion is unrelated to this patient’s presentation. Ectopic prolactin secretion (e.g., from a pituitary tumor or other sources) leads to galactorrhea and menstrual irregularities in older individuals, not precocious puberty.
C. Exogenous sex steroid exposure could lead to premature development of secondary sexual characteristics. However, in such cases, gonadotropins (FSH and LH) would be low due to suppression of the hypothalamic-pituitary axis.
D. A germline mutation in GNAS causes McCune-Albright syndrome, which is characterized by peripheral precocious puberty, café-au-lait spots, and fibrous dysplasia of the bones. In McCune-Albright syndrome, gonadotropins are typically suppressed (low FSH and LH), as estradiol is elevated independently of the hypothalamic-pituitary axis. This patient has no evidence of café-au-lait spots or skeletal abnormalities, and her gonadotropin levels are elevated, making this diagnosis unlikely.
E. 21-hydroxylase deficiency, the most common form of congenital adrenal hyperplasia, leads to excess adrenal androgens and ambiguous genitalia in females at birth or early virilization in childhood. This condition causes low cortisol, high ACTH, and elevated androgens (testosterone, androstenedione). This patient has normal genitalia, a normal ACTH level, and no evidence of hyperandrogenism.
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Question 22:
The correct answer is E. This 16-year-old male with delayed puberty, absence of pubic and facial hair, small penis and testicular size, and tall stature with a high BMI is most likely presenting with Klinefelter syndrome (47,XXY), which is caused by nondisjunction of the X chromosome during meiosis.
Klinefelter syndrome is a chromosomal disorder characterized by an extra X chromosome (47,XXY). It is one of the most common causes of primary hypogonadism in males. This patient’s clinical features, including tall stature, eunuchoid body habitus, small testicles, and lack of secondary sexual characteristics (e.g., facial and pubic hair), are classic findings. The underlying pathology is testicular dysfunction, leading to low testosterone levels and elevated gonadotropins (LH and FSH) due to a lack of negative feedback.
Incorrect answers:
A. This condition involves delayed onset of puberty with normal eventual development. However, this patient has physical findings (e.g., small testicles) indicative of primary hypogonadism, not just a constitutional delay.
B. This refers to conditions like Kallmann syndrome, which causes secondary hypogonadism. However, patients with Kallmann syndrome typically have a normal-sized testicle and anosmia, which are absent here.
C. This would result in primary hypogonadism but is less common and would not explain the constellation of tall stature and eunuchoid features.
D. This mutation causes congenital adrenal hyperplasia (CAH), which is associated with androgen excess, not deficiency. Male patients with CAH typically present with early virilization, not delayed puberty.
Question 23:
The correct answer is B. This newborn with ambiguous genitalia, hyponatremia, hyperkalemia, hypoglycemia, and metabolic acidosis is likely experiencing congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (most common form of CAH). This deficiency leads to impaired synthesis of cortisol and aldosterone, resulting in elevated ACTH, adrenal hyperplasia, and increased androgen production. The most appropriate pharmacotherapy is mineralocorticoid (aldosterone) and glucocorticoid replacement to address the hormonal imbalances.
Incorrect answers:
A. ACTH is elevated in this patient due to a lack of feedback inhibition by cortisol. Administering ACTH would worsen adrenal hyperplasia and increase androgen overproduction. The treatment goal is to suppress ACTH secretion by replacing deficient cortisol and aldosterone.
C. Androgen therapy is not appropriate because this patient already has excessive androgen production due to 21-hydroxylase deficiency. The goal of treatment is to reduce androgen overproduction by providing glucocorticoids to suppress ACTH.
D. The patient’s symptoms stem from defective adrenal steroidogenesis, not gonadotropin abnormalities. GnRH regulates the hypothalamic-pituitary-gonadal axis and is unrelated to the adrenal insufficiency seen in CAH.
E. Growth hormone deficiency does not explain this patient’s presentation. The ambiguous genitalia, electrolyte abnormalities, and hypoglycemia are classic for adrenal insufficiency due to 21-hydroxylase deficiency, not growth hormone deficiency.
Question 24:
The correct answer is C. Pericardial friction rub. This 59-year-old man has advanced chronic kidney disease (CKD) with severe uremia (BUN 65 mg/dL). A pericardial friction rub indicates uremic pericarditis, which is a life-threatening complication of renal failure and a definitive, absolute indication for immediate hemodialysis.
Incorrect answers:
A. Increasingly severe anemia is a common chronic complication of CKD due to decreased erythropoietin production; it is managed with recombinant erythropoietin and iron supplements, not emergent dialysis.
B. Moderate pedal edema reflects mild fluid overload in CKD, which is initially managed conservatively with loop diuretics rather than acute hemodialysis.
D. Persistent hypertension is a chronic manifestation of progressive CKD managed by optimizing multi-drug antihypertensive regimens (such as ACE inhibitors or ARBs) and fluid restrictions.
E. Recurrent episodes of hypoglycemia can occur in advanced CKD due to reduced renal clearance of insulin, requiring down-titration of his diabetes medications rather than dialytic intervention.
Question 25:
The correct answer is C. The points on the same curve represent the same contractility, meaning they correspond to the appropriate end-diastolic volume for a given cardiac output. The slope of the curve represents contractility, so any transition along the same curve (e.g., W to Y) occurs with unchanged contractility. This patient presents with findings suggestive of an acute STEMI in the anterolateral leads (ST-segment elevation in V4 to V6, new Q waves, and increased serum troponin I). In anterolateral STEMI, the left ventricular function is compromised due to reduced blood supply, leading to decreased contractility. The resulting decreased contractility reduces stroke volume, which decreases cardiac output and increases end-diastolic volume (blood left in the ventricle due to impaired ejection).
Question 26:
The correct answer is E. Spleen. The abdominal CT scan reveals a bright, metallic bullet causing a streak artifact on the left side of the upper abdomen. Anatomically, this solid organ located lateral to the stomach and adjacent to the left 10th intercostal space is the spleen.
Incorrect answers:
A. The left adrenal gland is a small, retroperitoneal structure located medially and superiorly to the kidney, not laterally.
B. The colon sits more anteriorly or inferiorly at this slice level and typically contains visible pocketed gas or stool.
C. The left kidney is situated more medially and posteriorly; the image shows the bullet passed lateral to it.
D. The lung bases are visible posteriorly at this thoracic-abdominal junction, but the bullet is lodged entirely within the solid abdominal organ.
Question 27:
The correct answer is C. This 66-year-old man with Parkinson disease is on carbidopa-levodopa therapy but continues to experience motor fluctuations such as freezing episodes, rigidity, and clumsiness. The adjunct therapy in question is most likely a MAO-B inhibitor, which helps enhance dopaminergic signaling by reducing the breakdown of dopamine in the brain.
Parkinson’s disease treatment typically begins with levodopa, a precursor of dopamine, in combination with carbidopa, which inhibits peripheral conversion of levodopa to dopamine, allowing more levodopa to reach the brain. MAO-B inhibitors (e.g., selegiline, rasagiline) are often used as adjunct therapy in Parkinson’s disease. These drugs inhibit the breakdown of dopamine in the brain, prolonging its effects and improving motor symptoms. This patient has on off phenomenon due to fluctuations in medication effectiveness, which cause patients to transition between periods of improved mobility (i.e., “on”) and the return of symptoms such as rigidity and tremors (i.e., “off”). adding monoamine oxidase type B inhibitor (e.g., selegiline or rasagiline), which prevents the central conversion of dopamine into DOPAC (i.e., 3,4-dihydroxyphenylacetic acid), can prolong the effect of the neurotransmitter.
Incorrect answers:
A. This enzyme converts levodopa to dopamine. Carbidopa already inhibits this enzyme peripherally, so further inhibition is unnecessary.
B. This enzyme converts dopamine to norepinephrine. It is unrelated to Parkinson’s disease treatment.
D. This enzyme converts norepinephrine to epinephrine and is unrelated to dopaminergic signaling in Parkinson disease.
E. This is the rate-limiting enzyme in dopamine synthesis. Inhibition of this enzyme would worsen Parkinson’s symptoms by decreasing dopamine synthesis.
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Question 28:
The correct answer is B. Muscle rigidity. This 33-year-old patient has developed Neuroleptic Malignant Syndrome (NMS), a life-threatening reaction to antipsychotic medication (olanzapine). NMS is characterized by altered mental status, autonomic instability (tachycardia, extreme hypertension, tachypnea), hyperthermia, and generalized “lead-pipe” muscle rigidity.
Incorrect answers:
A. Hyperreflexia and neuromuscular clonus are highly characteristic of Serotonin Syndrome rather than NMS. NMS typically presents with sluggish or decreased deep tendon reflexes due to severe muscle rigidity.
C. Mydriasis (dilated pupils) is typical of Serotonin Syndrome or sympathomimetic toxicity. In contrast, the pupillary examination in a patient with NMS is characteristically normal.
D. Petechial rash points toward systemic infectious etiologies such as meningococcemia or infective endocarditis. It is not a feature of idiosyncratic drug reactions like NMS.
E. Unilateral hemiparesis is a focal neurological deficit indicating an acute structural brain lesion like a stroke. NMS presents with symmetric, generalized neuromuscular changes instead.
Question 29:
The correct answer is E. This patient most likely has transitional cell carcinoma (TCC) of the renal pelvis, also known as urothelial carcinoma. Risk factors for this condition include smoking and occupational exposure to naphthylamine. The presentation fits with the typical features of TCC, including hematuria and possible associated symptoms. For USMLE, removed organs most likely indicate a malignant tumor or non-viable tissues. For example, in case of oncocytoma, the kidney is unlikely to be removed.
Incorrect answers:
A. Angiomyolipoma is associated with tuberous sclerosis, but there are no other features of this syndrome present in this case.
B. Melanoma would typically present with a pigmented lesion, often on the skin, and its risk factors include sun exposure and fair skin. This patient’s symptoms do not fit the presentation of melanoma.
C. Nephroblastoma (Wilms tumor) is most commonly seen in children, especially between the ages of 2 and 4. It is unlikely to present in an adult patient.
D. Oncocytomas are benign renal masses usually discovered incidentally during imaging for other conditions. They do not present with symptoms like those seen in this case.
Question 30:
The correct answer is A. Effect of alcohol on the condition. The clinical image and vignette demonstrate papulopustular rosacea, characterized by persistent centrofacial erythema, flushing, and a warm or burning sensation. Common triggers for rosacea flares include emotional stress, temperature changes, spicy foods, and alcohol (especially red wine, which this patient drinks weekly). Asking about the specific effect of alcohol helps confirm the clinical diagnosis by establishing a known lifestyle trigger.
Incorrect answers:
B. Excessive sweating is associated with conditions like hyperhidrosis or generalized autonomic dysfunction, but it is not a primary diagnostic criterion or a well-established precipitating factor for rosacea flares.
C. Family history of adenomas is relevant for genetic tumor syndromes like Lynch syndrome or FAP, which have no pathophysiological link or clinical association with rosacea or its centrofacial erythema.
D. Numbness of the fingers and toes evaluates for peripheral neuropathy, a common long-term complication of her type 1 diabetes mellitus. However, this is unrelated to the workup or confirmation of her acute dermatological condition.
E. Poor healing of skin lacerations checks for microvascular complications and poor glycemic control in patients with diabetes, but it does not aid in diagnosing or identifying the triggers of rosacea.
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Question 31:
The correct answer is B. Herd immunity. This 5-year-old unvaccinated girl has maintained good health because a high percentage of the surrounding population is vaccinated. Herd immunity occurs when a critical threshold of a community is immune to an infectious disease, indirectly protecting susceptible, unvaccinated individuals by reducing the overall chain of transmission.
Incorrect answers:
A. Community eradication of vaccine-preventable disease does not explain her ongoing safety, as very few diseases (such as smallpox) have been globally eradicated; most pathogens continue to circulate globally and can be reintroduced.
C. Lingering protection of maternal antibodies is incorrect because maternal IgG antibodies transferred across the placenta typically degrade and disappear within the first 6 to 12 months of life, offering no protection by age 5.
D. A normal immune system protects against opportunistic infections but cannot inherently prevent primary infection when an unvaccinated individual is exposed to highly contagious pathogens like measles or varicella.
E. Underdiagnosis of vaccine-preventable conditions is incorrect because public health surveillance for severe childhood vaccine-preventable diseases is robust, and her history explicitly notes she has never actually had a vaccine-preventable illness.
Question 32:
The correct answer is A. Binding to the D antigen on fetal erythrocytes. This Rh-negative mother is already alloimmunized, as indicated by a positive postpartum indirect Coombs titer of 1:32 from her first pregnancy. Rho(D) immune globulin (RhIg) contains anti-D IgG antibodies. When administered, these exogenous antibodies cross the placenta and target, coat, and cause the destruction of Rh-positive fetal RBCs in maternal circulation before the mother’s immune system can recognize them, specifically by binding to the D antigen on fetal erythrocytes.
Incorrect answers:
B. Blockade of complement binding to fetal erythrocytes is incorrect because RhIg functions via opsonization and subsequent macrophage clearance in the maternal spleen, rather than by altering complement activation pathways.
C. Induction of class switching by maternal B lymphocytes is incorrect because RhIg aims to prevent maternal B-cell activation entirely; it does not promote or accelerate immunoglobulin class switching.
D. Inhibition of production of fetal blood group A erythrocytes is incorrect because RhIg target specificity is limited entirely to the Rh(D) surface antigen and has no physiological impact on ABO erythrocyte production in the fetal bone marrow.
E. Prevention of fetal erythrocytes from entering maternal blood circulation is incorrect because RhIg cannot physically block or prevent fetomaternal hemorrhage, which naturally occurs during deliveries, trauma, or invasive procedures.
Question 33:
The correct answer is D. Purine degradation pathway. This 40-year-old man presents with acute podagra (edema, erythema, and exquisite tenderness of the right great toe) following alcohol and seafood consumption, which is a classic presentation of acute gouty arthritis. Gout is caused by the precipitation of monosodium urate crystals in joints due to hyperuricemia. Uric acid is the final product of the purine degradation pathway, and its accumulation is driven by dietary purines (seafood like lobster) and decreased renal excretion accelerated by alcohol consumption.
Incorrect answers:
A. Chylomicron processing pathway is involved in the transport of dietary lipids from the intestine to peripheral tissues. Flaws in this pathway lead to hyperchylomicronemia and eruptive xanthomas or pancreatitis, not urate crystal deposition.
B. Methionine regeneration pathway converts homocysteine back into methionine. Disruption of this pathway results in homocystinuria, which presents with ectopia lentis, marfanoid habitus, and early thromboembolism.
C. Pentose phosphate pathway generates NADPH and ribose-5-phosphate. While its overactivity could theoretically increase ribose-5-phosphate availability for purine synthesis, the direct cause of gout is an accumulation of downstream degradation pathway intermediates (uric acid).
E. Urea cycle functions to convert toxic ammonia into non-toxic urea for renal excretion. Inborn errors or failure of this cycle manifest as hyperammonemia, causing lethargy, vomiting, and progressive encephalopathy rather than localized arthritis.
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Question 34:
The correct answer is A. “Do you have any concerns about your alcohol use?”. When a patient discloses a substance-related adverse event (such as a DUI), the physician must explore potential problematic drinking using open-ended, nonjudgmental inquiry. Asking “Do you have any concerns about your alcohol use?” is an effective first step in motivational interviewing. It builds therapeutic rapport, prevents defensiveness, and allows the clinician to gauge the patient’s insight and current stage of change (e.g., precontemplation vs. contemplation).
Incorrect answers:
B. “How has your alcohol use been this week compared to last week…” is a closed-ended, narrow comparative question. This style limits the patient’s ability to elaborate and is best reserved for gathering specific quantitative data after initial rapport and insight have been established.
C. “So you’re here because you’re concerned about your alcohol use…” is an assumption-based, presumptive statement. Misrepresenting the patient’s stated reason for the visit (which was a routine exam) can provoke defensiveness and damage the physician-patient dynamic.
D. “When was your last drink?” is a direct, closed-ended question used to map the timeline of recent consumption. This is clinically vital when managing a patient at acute risk for alcohol withdrawal syndrome (characterized by tremors, tachycardia, or diaphoresis), which is absent on this patient’s normal physical exam.
E. “Would you be willing to go through a detoxification program?” is a premature, action-oriented intervention. Supervised detoxification is indicated for patients with severe physiological dependence. Recommending intensive treatment before assessing the patient’s readiness to change typically breeds resistance.
Question 35:
The correct answer is C. Mesoderm. This 4-year-old girl has primary lymphedema, as evidenced by slowly progressive swelling of her lower extremity and lymphoscintigraphy showing anomalous development of the lymphatic vessels. The cardiovascular system, including the vascular endothelium, lymphatic vessels, microcirculation, and spleen, is entirely derived from the embryonic mesoderm.
Incorrect answers:
A. Ectoderm gives rise to the central and peripheral nervous systems, the epidermis of the skin, hair, nails, subcutaneous glands, and the lens of the eye, rather than the deep endothelial or lymphatic networks.
B. Endoderm differentiates into the epithelial linings of the gastrointestinal tract, respiratory tract, urinary bladder, and urethra, as well as parenchyma of organs like the liver and pancreas.
D. Neural crest cells (a specialized population derived from ectoderm) migrate to form structures such as the peripheral ganglia, melanocytes, craniofacial cartilage, and adrenal medulla, but do not differentiate into peripheral lymphatics.
E. Neuroectoderm develops directly into the central nervous system (brain and spinal cord), neurohypophysis, pineal gland, and the retinas, rather than peripheral mesenchymal systems.
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Question 36:
The correct answer is B. This patient has obstructive sleep apnea (OSA) as evidenced by daytime somnolence. The patient also has features of obesity hypoventilation syndrome (OHS), including severe obesity (BMI of 63), cyanosis, and abnormal arterial blood gas findings indicating respiratory acidosis (pH 7.31, high PCO2 of 70, and low PO2). Chronic hypoxia stimulates hypoxia-inducible factor 2 (HIF-2), which increases erythropoietin production and results in elevated hemoglobin and red blood cell mass. OSA patients may present with Hypertension (due to hypoxia), Depression or Atrial fibrillation (due to HTN, Atrial enlargement).
Incorrect answers:
A. In respiratory acidosis, the proper metabolic compensation is metabolic alkalosis, not acidosis. This patient’s bicarbonate would be elevated, not decreased.
C. Obesity causes extrinsic restrictive lung disease, which reduces total lung capacity (TLC). Therefore, TLC should be decreased, not increased.
D. Chronic hypoxia can lead to generalized pulmonary vasoconstriction, causing pulmonary hypertension, which increases pressure in the right ventricle and leads to right ventricular hypertrophy. The left ventricle is not typically affected in this scenario.
Question 37:
The correct answer is B. This 5-year-old girl presents with bloody diarrhea, anemia, thrombocytopenia, acute kidney injury (elevated creatinine), and hypertension. These findings are consistent with hemolytic uremic syndrome (HUS), which is most commonly caused by Shiga toxin-producing Escherichia coli (STEC), particularly the O157:H7 serotype.
HUS is a triad of:
- Microangiopathic hemolytic anemia: Evidenced by pallor, low hemoglobin (8.5 g/dL), and schistocytes (fragmented RBCs) on a peripheral blood smear.
- Thrombocytopenia: Low platelet count (45,000/mm³) due to platelet consumption in small thrombi.
- Acute kidney injury (AKI): Elevated creatinine (3.3 mg/dL), oliguria, and hypertension due to renal vascular damage.
HUS is typically triggered by infection with Shiga toxin-producing E. coli (STEC), which releases Shiga-like toxin. The toxin:
- Damages endothelial cells in the glomeruli, leading to platelet aggregation and microthrombi formation.
- Causes hemolysis as red blood cells are sheared passing through damaged vessels.
- Results in renal failure due to microvascular occlusion in the kidneys.
The clinical course:
- Initial episode of bloody diarrhea (due to intestinal damage caused by the STEC).
- Progression to HUS within a week, as seen in this patient with worsening kidney function and anemia after the diarrhea subsided.
Incorrect answers:
A. Although Campylobacter jejuni can cause bloody diarrhea, it is not associated with HUS.
C. Rotavirus typically causes non-bloody diarrhea in young children and is not associated with HUS.
D. Salmonella can cause gastroenteritis and bacteremia but does not produce Shiga toxin or cause HUS.
E. Yersinia pestis causes plague, a systemic infection associated with fever, lymphadenopathy, and sepsis, not diarrhea or HUS.
Question 38:
The correct answer is C. This patient’s intermittent headache is likely a symptom of poorly controlled hypertension (154/100 mmHg). The ECG findings of tall R waves in leads V5-V6 and left axis deviation are indicative of left ventricular hypertrophy (LVH). LVH develops as an adaptive response to chronic hypertension, where there is increased synthesis of contractile filaments (actin and myosin) within existing myocytes, leading to myocyte hypertrophy rather than hyperplasia. In chronic HTN, sarcomeres are added in parallel.
Incorrect answers:
A. Excessive accumulation of glycogen is characteristic of glycogen storage diseases such as Pompe disease, which typically causes cardiomyopathy or systemic symptoms unrelated to the hypertrophic changes seen in this patient.
B. Fibrosis of intraventricular conduction pathways can lead to conduction abnormalities and arrhythmias. However, the occasional skipped beats described in this patient are more consistent with benign premature atrial contractions (PACs) and do not explain the LVH.
D. Misfolding and aggregation of cytoskeletal proteins result in dilated cardiomyopathy (DCM), not LVH. DCM is characterized by ventricular dilation and systolic dysfunction, which are not evident in this patient.
E. Myocyte hyperplasia refers to an increase in the number of myocytes, which is not a mechanism for hypertrophy. In LVH, the adaptive response involves increased actin and myosin synthesis within existing myocytes rather than cell proliferation.
Question 39:
The correct answer is B. Cytochrome P450. This scenario describes the metabolic activation of pro-carcinogens. Benzene and polycyclic aromatic hydrocarbons (found in cigarette smoke) are not inherently carcinogenic; they must first be oxidized and biotransformed by Phase I microsomal enzymes—specifically the Cytochrome P450 system (such as CYP2E1 for benzene)—into highly reactive, electrophilic intermediates (like benzene oxide) that bind to DNA and cause mutations.
Incorrect answers:
A. Aldehyde dehydrogenase converts toxic aldehydes into non-toxic carboxylic acids (e.g., acetaldehyde to acetate during ethanol metabolism). It is involved in detoxification rather than the harmful metabolic activation of polycyclic hydrocarbons or benzene.
C. Glutathione S-transferase is a Phase II conjugation enzyme that couples reduced glutathione to electrophilic compounds. It acts to neutralize and detoxify reactive intermediates, so a polymorphism reducing its activity—not one causing activation—would increase cancer risk.
D. Methyltransferase is a Phase II enzyme responsible for transferring methyl groups to substrate molecules (such as TPMT or COMT). It is primarily involved in inactivating drugs or neurotransmitters rather than activating environmental pro-carcinogens.
E. Succinate dehydrogenase is an inner mitochondrial membrane enzyme that participates simultaneously in the citric acid cycle and the electron transport chain (Complex II). It plays no role in the metabolic activation or clearance of xenobiotics like benzene.
Question 40:
The correct answer is B. Phase 1.This investigator is assessing the maximum tolerated dose, safety profile, and pharmacokinetics of a new antimalarial drug in a small cohort (80 healthy volunteers). This perfectly describes Phase 1 of clinical drug trials, which focuses on assessing safety, toxicity, pharmacokinetics, and pharmacodynamics in a small group of healthy individuals (or patients with advanced disease for oncology trials) before moving into larger patient populations.
Incorrect answers:
A. Phase 0 consists of microdosing studies conducted very early in human development using subtherapeutic doses in a tiny cohort (<15 people) to evaluate basic pharmacokinetics and cellular targets, not to determine the maximum tolerated dose.
C. Phase 2 clinical trials expand testing to a moderate group of patients (typically 100–300) who actually have the target disease (e.g., individuals with active malaria infection) to evaluate optimal dosing strategies and initial treatment efficacy.
D. Phase 3 trials involve large-scale, often multicenter randomized controlled testing in hundreds to thousands of affected patients. The primary goal is to definitively confirm efficacy, compare the new drug against the current standard of care, and detect rare adverse profiles.
E. Phase 4 clinical trials comprise post-marketing surveillance conducted after the drug has received regulatory FDA approval. This phase monitors the long-term safety, real-world effectiveness, and very rare side effects of the drug across the general population over time.
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