Pharmacognosy and Phytotherapy
Core concepts
Know the major plant-derived drug classes and their representative compounds: alkaloids (morphine from opium poppy, atropine from belladonna, caffeine, quinine, vinca alkaloids), glycosides (cardiac glycosides such as digoxin from foxglove; cyanogenic glycosides), terpenes and essential oils (menthol, thymol), and polyphenols (tannins, flavonoids). Understand that secondary metabolites serve the plant's defense and that their content varies with species, part used, harvest time, and extraction method.
Quality and standardization
Learn why herbal preparations are standardized to a marker compound, and the difference between a standardized extract and a traditional preparation. Recognize adulteration and substitution risks, and the need for identity testing (macroscopic, microscopic, chromatographic). Understand common herb–drug interactions: St John's wort (CYP3A4/P-gp induction reducing efficacy of many drugs), ginkgo and ginseng (bleeding risk with anticoagulants), licorice (mineralocorticoid effect, hypokalemia and hypertension), and grapefruit (CYP3A4 inhibition).
Traps in questions
- Assuming 'natural' means safe or free of interactions.
- Confusing the plant source of a drug with its semisynthetic derivatives.
- Forgetting that standardization to a marker does not guarantee the same clinical effect.
- Mixing up stimulant (caffeine, ephedra) with sedative botanicals (valerian).
Worked example (rule of thumb)
When a patient on warfarin adds a supplement and the INR falls, think enzyme induction (St John's wort) rather than inhibition; when INR rises with a new supplement, think bleeding-risk herbs (ginkgo, garlic, ginseng) or CYP inhibition. Pair each herb with its mechanism and the affected drug class.