Herbal drug–food interactions with examples MCQs With Answer

Introduction: This quiz collection focuses on herbal drug–food interactions relevant to M.Pharm students studying Herbal and Cosmetic Analysis (MPA 204T). Understanding these interactions is critical for predicting altered pharmacokinetics and pharmacodynamics, ensuring patient safety, and advising on concomitant use of herbs, foods and conventional drugs. The questions cover mechanisms such as CYP450 and P‑glycoprotein modulation, transporter effects, pharmacodynamic synergy (bleeding or serotonergic risk), and representative clinical examples (e.g., St. John’s wort, grapefruit, garlic, ginkgo, green tea). Each MCQ tests conceptual depth and practical counseling points to prepare students for research, clinical evaluation and rational therapeutic guidance.

Q1. Which mechanism best explains how St. John’s wort reduces plasma concentrations of many co‑administered drugs?

• Inhibition of intestinal CYP3A4 and P‑glycoprotein
• Induction of hepatic and intestinal CYP3A4 and P‑glycoprotein
• Chelation with metal ions in the gastrointestinal tract
• Inhibition of renal tubular secretion via OCT transporters

Correct Answer: Induction of hepatic and intestinal CYP3A4 and P‑glycoprotein

Q2. Grapefruit juice increases systemic exposure of certain oral drugs primarily by which of the following?

• Induction of hepatic CYP2D6 enzymes
• Inhibition of intestinal CYP3A4 through furanocoumarins
• Activation of P‑glycoprotein efflux in enterocytes
• Enhancement of renal clearance via increased GFR

Correct Answer: Inhibition of intestinal CYP3A4 through furanocoumarins

Q3. Concomitant use of garlic supplements with warfarin most commonly leads to which clinical effect?

• Reduced anticoagulant effect due to induction of CYP2C9
• No interaction; garlic only affects cholesterol
• Enhanced anticoagulant and antiplatelet effect, increasing bleeding risk
• Accelerated warfarin metabolism via increased renal excretion

Correct Answer: Enhanced anticoagulant and antiplatelet effect, increasing bleeding risk

Q4. Regular consumption of green tea may reduce the anticoagulant effect of warfarin because green tea contains which component?

• High amounts of furanocoumarins that inhibit CYP3A4
• High vitamin K content that decreases warfarin INR
• Piperine which induces CYP2C9
• Ginkgolides that increase platelet aggregation

Correct Answer: High vitamin K content that decreases warfarin INR

Q5. Which herbal supplement is most associated with increased bleeding risk when combined with aspirin or other anticoagulants?

• Ginkgo biloba
• St. John’s wort
• Licorice (Glycyrrhiza)
• Goldenseal (Hydrastis)

Correct Answer: Ginkgo biloba

Q6. Piperine in black pepper increases bioavailability of co‑administered drugs mainly by which action?

• Inducing UDP‑glucuronosyltransferases to increase clearance
• Inhibiting CYP3A4 and P‑glycoprotein, reducing first‑pass metabolism
• Blocking renal organic anion transporters to decrease secretion
• Acting as a chelating agent to reduce absorption

Correct Answer: Inhibiting CYP3A4 and P‑glycoprotein, reducing first‑pass metabolism

Q7. The principal grapefruit constituents responsible for drug interactions belong to which chemical class?

• Flavonoids (e.g., quercetin)
• Furanocoumarins (e.g., bergamottin)
• Alkaloids (e.g., morphine‑like)
• Saponins (e.g., glycyrrhizin)

Correct Answer: Furanocoumarins (e.g., bergamottin)

Q8. Hyperforin, a constituent of St. John’s wort, activates which receptor to cause enzyme induction?

• Vitamin D receptor (VDR)
• P‑glycoprotein receptor (PXR) / Pregnane X receptor (PXR)
• Nuclear factor kappa B (NF‑κB)
• Peroxisome proliferator‑activated receptor gamma (PPAR‑γ)

Correct Answer: P‑glycoprotein receptor (PXR) / Pregnane X receptor (PXR)

Q9. Cranberry juice has been reported to interact with warfarin resulting in which outcome?

• Marked decrease in INR and clotting risk
• No interaction due to complete hepatic inactivation
• Possible increase in INR and bleeding risk
• Acceleration of warfarin renal clearance

Correct Answer: Possible increase in INR and bleeding risk

Q10. Curcumin (turmeric) co‑administration with anticoagulants is a concern because curcumin can:

• Potentiate anticoagulant effect by inhibiting platelet aggregation and CYP enzymes
• Completely block warfarin absorption by chelation
• Induce CYP2C9, reducing warfarin concentration
• Act only as a gastric protectant without systemic effects

Correct Answer: Potentiate anticoagulant effect by inhibiting platelet aggregation and CYP enzymes

Q11. Which herbal supplement is well documented to reduce the efficacy of oral contraceptives?

• Echinacea
• St. John’s wort
• Ginkgo biloba
• Milk thistle

Correct Answer: St. John’s wort

Q12. Combining St. John’s wort with selective serotonin reuptake inhibitors (SSRIs) primarily risks which adverse effect?

• Serotonin syndrome due to increased serotonergic activity
• Severe hypokalemia from renal loss
• Increased blood glucose due to CYP2C9 induction
• Excessive sedation via GABAergic potentiation

Correct Answer: Serotonin syndrome due to increased serotonergic activity

Q13. Green tea catechins can reduce oral absorption of some drugs by inhibiting which transporter in the intestine?

• Organic anion transporting polypeptides (OATP1A2/OATP2B1)
• Multidrug resistance protein 2 (MRP2)
• Glucose transporter 4 (GLUT4)
• Renal OCT2 transporter

Correct Answer: Organic anion transporting polypeptides (OATP1A2/OATP2B1)

Q14. A patient on cyclosporine begins an herbal regimen and later shows reduced cyclosporine trough levels. Which herb is the most likely cause?

• Goldenseal (Hydrastis canadensis)
• St. John’s wort (Hypericum perforatum)
• Ginkgo biloba
• Licorice (Glycyrrhiza glabra)

Correct Answer: St. John’s wort (Hypericum perforatum)

Q15. Chronic ingestion of licorice (glycyrrhizin) can produce pseudoaldosteronism. Which of the following is a typical effect relevant to drug interactions?

• Hyperkalemia and hypotension that enhance ACE inhibitor effects
• Hypokalemia and hypertension that may potentiate digoxin toxicity
• Increased INR when combined with warfarin
• Reduced absorption of lipophilic drugs due to increased bile flow

Correct Answer: Hypokalemia and hypertension that may potentiate digoxin toxicity

Q16. Which cytochrome enzyme is mainly responsible for metabolizing S‑warfarin and is a common site of herb‑induced interaction altering INR?

• CYP3A4
• CYP2C9
• CYP1A2
• CYP2D6

Correct Answer: CYP2C9

Q17. High dietary intake of which food is classically known to antagonize warfarin therapy by supplying vitamin K?

• Spinach and other leafy green vegetables
• Grapefruit and citrus fruits
• Dairy milk and yogurt
• Refined sugars and sweet beverages

Correct Answer: Spinach and other leafy green vegetables

Q18. Which herbal product is recognized for inhibiting platelet function and thereby increasing bleeding risk when combined with NSAIDs or anticoagulants?

• Ginger (Zingiber officinale)
• St. John’s wort
• Goldenseal
• Black cohosh

Correct Answer: Ginger (Zingiber officinale)

Q19. Goldenseal (Hydrastis) is clinically important because it tends to:

• Induce CYP3A4 and reduce drug exposure
• Inhibit CYP3A4 and increase plasma concentrations of substrates
• Act as a strong OATP1B1 inducer in the liver
• Bind to bile acids and impair fat absorption

Correct Answer: Inhibit CYP3A4 and increase plasma concentrations of substrates

Q20. For herbal supplements that increase bleeding risk (e.g., ginkgo, garlic, ginseng, ginger), what is a commonly recommended preoperative discontinuation period?

• Stop at least 24 hours before surgery
• Stop at least 7 days before surgery
• Stop immediately before anesthesia with no prior discontinuation
• No discontinuation needed for herbal products

Correct Answer: Stop at least 7 days before surgery

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