Pharmacognosy and Natural Products
This domain tests natural-product sources, active constituents, quality control, and the evidence and risk attached to botanical medicines. Expect source–constituent matching, adulteration and standardisation questions, and clinically important herb–drug interactions.
Source to constituent
Alkaloids: morphine and codeine from Papaver somniferum, quinine and quinidine from Cinchona bark, vincristine and vinblastine from Catharanthus roseus, atropine from Atropa belladonna, caffeine from Coffea. Cardiac glycosides: digoxin from Digitalis lanata. Anthraquinones: sennosides from Senna. Terpenoids: artemisinin from Artemisia annua, paclitaxel from Taxus brevifolia. Phenolics: silymarin from milk thistle, curcumin from turmeric.
Standardisation and quality
Extracts are standardised to a marker constituent - ginkgo to ginkgolides and bilobalide, St John's wort to hypericin or hyperforin - and expressed as extract ratios such as 5:1. Identity testing uses macroscopic and microscopic examination, thin-layer chromatography and HPLC fingerprints. Contaminants include heavy metals, pesticides, microbial load and adulterants; a classic case is ginkgo leaf adulterated with flavonoid-rich rutin.
Safety and interactions
St John's wort induces CYP3A4 and P-glycoprotein, lowering ciclosporin, tacrolimus, combined oral contraceptive and warfarin concentrations. Ginkgo and ginseng add bleeding risk with anticoagulants. Liquorice causes pseudoaldosteronism with hypokalaemia and hypertension. Kava is hepatotoxic. Grapefruit furanocoumarins inhibit intestinal CYP3A4.
Worked example
A patient on warfarin reports a falling INR after starting a self-selected low-mood supplement. Hyperforin in St John's wort induces CYP3A4, accelerating warfarin metabolism, and induces intestinal P-glycoprotein, reducing absorption. Action: identify the product, advise stopping it (enzyme induction persists up to two weeks after the last dose), avoid other interacting medicines, and recheck INR.
Traps
- Treating "natural" as "safe" and leaving it off the medication history.
- Assuming one batch equals another; content varies with species, plant part, season and extraction.
- Confusing common names - "ginseng" covers several Panax species with different profiles.