Pharmacognosy and Phytotherapy
Core concepts
This domain links natural-product chemistry to herbal medicines. Candidates must know the principal secondary-metabolite classes - alkaloids (e.g. morphine, atropine, quinine, caffeine), glycosides (cardiac glycosides such as digoxin; saponins), terpenes and essential oils (menthol, thymol), flavonoids, tannins, and coumarins - and the plants that yield them. Understand extraction and standardisation: maceration, percolation, infusion/decoction, and the meaning of a standardised extract (a defined marker constituent). Know pharmacopoeial quality requirements for herbal drugs (identity, assay, limits for foreign matter, heavy metals, pesticides, aflatoxins) and the herbal–drug interaction risks: St John's wort (CYP3A4 induction, reducing efficacy of oral contraceptives and warfarin), ginkgo (bleeding risk with anticoagulants), ginseng, and liquorice (mineralocorticoid effect, hypokalaemia).
Traps
Examiners test plant–constituent–effect mapping (e.g. Digitalis purpurea → cardiac glycosides → positive inotropy; Atropa belladonna → tropane alkaloids → anticholinergic). Another trap is confusing a herbal 'traditional use' claim with an evidence-based indication, and forgetting that 'natural' does not mean safe or interaction-free.
Rule of thumb
For any herbal question, name three things: the plant, the chemical class of the active constituent, and the pharmacological or toxic effect. For interaction questions, remember enzyme induction (St John's wort, rifampicin-like) reduces co-administered drug levels.
Worked example
A patient on warfarin starts St John's wort. The herb induces CYP3A4 and increases warfarin metabolism, lowering the INR and risking thromboembolism; the correct advice is to avoid the combination and monitor INR closely.