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Pharmacology

Adverse Drug Reactions and Interactions Practice Questions

19 free Adverse Drug Reactions and Interactions practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 19 Medium

Which of the following best describes a Type A adverse drug reaction (ADR)?

  1. A An unpredictable immune-mediated allergic reaction
  2. B Dose-related exaggeration of the drug's effect
  3. C A reaction occurring only on first drug exposure
  4. D An idiosyncratic host metabolic error

Correct answer: Dose-related exaggeration of the drug's effect

Type A ADRs are dose-related and result from an exaggeration of the drug’s normal pharmacological action. They tend to be predictable and often reversible by dose reduction or stopping the drug.

Question 2 of 19 Medium

Which is an example of a Type B (idiosyncratic) adverse drug reaction?

  1. A Hypotension from an antihypertensive
  2. B Bleeding from warfarin overdose
  3. C Anaphylaxis after penicillin exposure
  4. D Sedation after benzodiazepines

Correct answer: Anaphylaxis after penicillin exposure

Type B reactions are unpredictable and not dose-dependent; true drug allergies such as IgE-mediated anaphylaxis to penicillin are typical examples.

Question 3 of 19 Medium

A patient on warfarin starts a new drug that inhibits CYP2C9. What is the most likely consequence?

  1. A Reduced warfarin effect and clotting risk
  2. B Increased warfarin levels and bleeding risk
  3. C No change in warfarin effect
  4. D Warfarin converts to inactive metabolite

Correct answer: Increased warfarin levels and bleeding risk

Inhibition of CYP2C9 reduces warfarin metabolism, increasing its plasma concentration and enhancing anticoagulant effect, leading to bleeding.

Question 4 of 19 Medium

Which mechanism underlies many serious drug–drug interactions (DDIs)?

  1. A Competitive receptor antagonism
  2. B Changes in CYP450-mediated metabolism
  3. C Altered drug taste
  4. D Synergistic beneficial effects

Correct answer: Changes in CYP450-mediated metabolism

Many DDIs occur because one drug inhibits or induces CYP450 enzymes, altering the clearance of another drug and thus leading to toxicity or therapeutic failure.

Question 5 of 19 Medium

Grapefruit juice can increase plasma levels of certain medications by inhibiting which enzyme in the gut and liver?

  1. A CYP1A1
  2. B CYP3A4
  3. C MAO-A
  4. D CYP2D6

Correct answer: CYP3A4

Grapefruit juice contains furanocoumarins that irreversibly inhibit CYP3A4 in intestinal and hepatic cells, reducing first-pass metabolism and increasing drug concentrations.

Question 6 of 19 Medium

Which combination is especially dangerous due to additive risk of QT prolongation and torsades de pointes?

  1. A Warfarin + aspirin
  2. B Macrolide antibiotic + antiarrhythmic
  3. C ACE inhibitor + diuretic
  4. D Beta-blocker + calcium channel blocker

Correct answer: Macrolide antibiotic + antiarrhythmic

Some macrolides and antiarrhythmic drugs both prolong the QT interval. When combined, this additive effect increases risk of torsades de pointes and sudden cardiac death.

Question 7 of 19 Medium

Which factor increases the risk of adverse drug reactions in a patient?

  1. A Young age
  2. B Polypharmacy (multiple drugs)
  3. C Normal renal and hepatic function
  4. D Monotherapy with a well-tolerated drug

Correct answer: Polypharmacy (multiple drugs)

Taking multiple medications increases the likelihood of drug–drug interactions and adverse reactions. Polypharmacy is a major risk factor for ADRs.

Question 8 of 19 Medium

Which scenario best illustrates a pharmacodynamic drug–drug interaction?

  1. A CYP enzyme inhibition by one drug reducing the clearance of another
  2. B Competition for renal excretion causing increased levels
  3. C Two drugs that both depress respiratory center effects when combined
  4. D One drug binding to plasma protein displacing another

Correct answer: Two drugs that both depress respiratory center effects when combined

Pharmacodynamic interactions occur when drugs influence the same physiological pathway; additive depressant effects (e.g., CNS or respiratory) increase toxicity risk.

Question 9 of 19 Medium

A patient develops neutropenia after a course of chloramphenicol. This ADR is best classified as which type?

  1. A Type A (predictable)
  2. B Type B (idiosyncratic)
  3. C Type C (chronic)
  4. D Type D (delayed)

Correct answer: Type B (idiosyncratic)

Chloramphenicol–induced aplastic anemia or neutropenia is unpredictable and not dose-related, fitting criteria for a Type B (idiosyncratic) ADR.

Question 10 of 19 Medium

Which of the following increases the risk of toxicity when a drug with narrow therapeutic index is given with a strong CYP inhibitor?

  1. A Short half-life
  2. B High therapeutic index
  3. C Liver enzyme induction
  4. D Decreased hepatic clearance

Correct answer: Decreased hepatic clearance

A strong CYP inhibitor decreases hepatic clearance, raising drug levels — especially problematic for drugs with narrow therapeutic windows, increasing risk of toxicity.

Question 11 of 19 Medium

A patient experiences Stevens–Johnson syndrome after starting a sulfonamide antibiotic. What kind of ADR is this?

  1. A Dose-dependent toxicity
  2. B Allergic/hypersensitivity reaction
  3. C Therapeutic failure
  4. D Pharmacodynamic tolerance

Correct answer: Allergic/hypersensitivity reaction

Stevens–Johnson syndrome is a severe hypersensitivity reaction (immune-mediated), not predictable from dose or pharmacology, and thus classified as an allergic ADR.

Question 12 of 19 Medium

Which of the following drug–drug combinations should be avoided because of high risk of serious toxicity due to interaction via CYP3A4 inhibition?

  1. A Erythromycin + simvastatin
  2. B Amoxicillin + metformin
  3. C Hydrochlorothiazide + lisinopril
  4. D Aspirin + ibuprofen

Correct answer: Erythromycin + simvastatin

Erythromycin is a known CYP3A4 inhibitor. When combined with simvastatin (metabolized by CYP3A4), it can substantially increase statin levels and risk of rhabdomyolysis or other statin-associated toxicities.

Question 13 of 19 Medium

When a patient’s renal function declines markedly, what happens to clearance and risk of drug toxicity for renally excreted drugs?

  1. A Renal clearance increases, risk decreases
  2. B Renal clearance decreases, risk increases
  3. C Clearance unaffected, risk unaffected
  4. D Clearance increases, risk increases

Correct answer: Renal clearance decreases, risk increases

Reduced renal function lowers drug clearance, leading to accumulation and heightened risk of toxicity when drugs are predominantly renally eliminated.

Question 14 of 19 Medium

Which of the following describes a beneficial drug–drug interaction (rather than a harmful one)?

  1. A Combination precipitates dangerous serotonin syndrome
  2. B Two hepatotoxic drugs cause additive liver injury
  3. C ACE inhibitor eases calcium channel blocker edema
  4. D Macrolide raises statin levels causing myopathy

Correct answer: ACE inhibitor eases calcium channel blocker edema

Some interactions yield therapeutic benefit—for example, ACE inhibitors may mitigate peripheral edema caused by calcium channel blockers, improving tolerability.

Question 15 of 19 Medium

In older adults, why is the risk of adverse drug reactions higher than in younger adults?

  1. A Increased hepatic CYP enzyme metabolism
  2. B Improved renal drug clearance capacity
  3. C Organ decline combined with polypharmacy
  4. D Better inherent tolerance to drugs

Correct answer: Organ decline combined with polypharmacy

Elderly patients often have impaired hepatic or renal function and take multiple drugs (polypharmacy), both of which increase the probability of ADRs and interactions.

Question 16 of 19 Medium

Which of the following is true about drug interactions involving food or beverages?

  1. A They reliably improve a drug's effectiveness
  2. B They interfere solely with drug absorption
  3. C They may change drug metabolism or efficacy
  4. D They pose little risk of drug toxicity

Correct answer: They may change drug metabolism or efficacy

Food or beverages (e.g., grapefruit juice) can inhibit metabolizing enzymes or transporters and thereby alter drug exposure, leading to increased toxicity or reduced efficacy.

Question 17 of 19 Medium

A patient on two drugs that both depress bone marrow function is at increased risk for severe neutropenia. This is an example of which type of interaction?

  1. A Pharmacokinetic
  2. B Additive pharmacodynamic
  3. C Synergistic beneficial
  4. D Pharmacogenetic

Correct answer: Additive pharmacodynamic

When two drugs produce similar adverse effects (bone marrow suppression), their effects add up, increasing risk of toxicity — a classic pharmacodynamic interaction.

Question 18 of 19 Medium

What is the first step in evaluating a suspected adverse drug reaction in a patient?

  1. A Immediately discontinue every current medication
  2. B Take a detailed drug and timing history
  3. C Start empiric high-dose systemic steroids
  4. D Ignore it if the reaction seems mild

Correct answer: Take a detailed drug and timing history

A detailed history including timing of drug initiation relative to symptom onset is critical for attributing causality to an ADR and distinguishing it from other causes.

Question 19 of 19 Medium

Which statement about drug–drug interactions is correct?

  1. A Risk decreases as more medications are combined
  2. B Interactions can only reduce a drug's effect
  3. C Some interactions cause serious, preventable toxicity
  4. D Only prescription medications can interact harmfully

Correct answer: Some interactions cause serious, preventable toxicity

Some DDIs can cause serious or life-threatening adverse effects (e.g., bleeding, arrhythmia). Many are preventable by reviewing drug regimens and avoiding hazardous combinations.

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