Pharmacognosy and Natural Products
Core concepts
Understand the sources, classes, and uses of natural products: alkaloids (morphine, quinine, caffeine), glycosides (digitalis, salicin), terpenes and essential oils, flavonoids, tannins, and polysaccharides. Know the plant parts used, active constituents, and therapeutic uses. Familiarise yourself with standardisation, adulteration, and quality control (identity, assay, contamination). Recognise important herb–drug interactions: St John's wort (CYP3A4 induction), ginkgo (bleeding risk), ginseng, and liquorice (hypertension, hypokalaemia). Understand the principles of extraction (maceration, percolation, distillation) and the difference between a tincture, infusion, decoction, and extract.
Traps
Do not confuse the plant source with the active constituent. Alkaloid names often end in '-ine' but not always. St John's wort induces enzymes and reduces efficacy of many drugs - a frequent trap. Herbal products are not automatically safe because they are 'natural'. Standardisation refers to a marker compound, not necessarily the active one. Watch for adulteration and contamination questions.
Worked rule of thumb
If a question describes a patient on a narrow-therapeutic-index drug (e.g., warfarin, ciclosporin) starting an herbal product, suspect an interaction and recommend review or avoidance.
Exam strategy
For each herb, recall source → active class → use → key interaction or toxicity.