Herbal products and dietary supplements
Plant extracts and purified substances sold as supplements. Evidence of benefit is often weak, while interactions and liver injury are real risks.
What they are
A broad group: whole-plant extracts (St John's wort, ginkgo, garlic, ginseng, echinacea, kava, valerian, saw palmetto, red yeast rice) and purified substances (glucosamine, coenzyme Q10). In the United States they are sold without approval as medicines, so content and purity vary between products and batches. Clinicians need to ask about them because several change the effect of prescription medicines.
Mechanism of action
Each product has its own active constituents. The clinically important actions are few and well described: hyperforin in St John's wort induces CYP3A4 and P-glycoprotein through the nuclear receptor PXR; garlic, ginkgo and ginseng have antiplatelet effects; red yeast rice contains monacolin K, the same molecule as lovastatin; coenzyme Q10 resembles vitamin K; kava can injure the liver.
Target: Varies: PXR and CYP enzymes, platelets, HMG-CoA reductase, unknown targets
Drugs in this class
- St John's wortA plant extract (Hypericum perforatum) that may help mild to moderate depression but induces CYP3A4 and…Pregnane X receptor (PXR), which switches on CYP3A4 and P-glycoprotein; also monoamine reuptake
- GinkgoLeaf extract of the Ginkgo biloba tree, promoted for memory. Large trials found no protection against dementia; it may…Platelet-activating factor and vascular tone (proposed)
- GarlicAllium sativum supplements, promoted for cholesterol and blood pressure. Modest lipid effects at best; they can add to…Platelets and cholesterol synthesis (allicin and related sulfur compounds)
- GinsengRoot of Panax ginseng (Asian ginseng), promoted for energy and cognition. Small studies only; it can lower blood sugar…Multiple targets of ginsenosides (proposed)
- EchinaceaDaisy-family plants promoted to boost immunity against colds. It may slightly lower the chance of catching a cold…Immune cells (proposed immune stimulation)
- KavaA South Pacific pepper plant (Piper methysticum) used for anxiety. It is linked to rare, sometimes fatal, liver injury.Central nervous system (kavalactones; mechanism not established)
- ValerianRoot of Valeriana officinalis, promoted for sleep. Evidence is inconsistent, and sleep guidelines advise against it…Central nervous system (mechanism not established)
- Saw palmettoBerry extract of Serenoa repens, promoted for urinary symptoms of an enlarged prostate. Trials show little or no…5-alpha reductase (inhibited in vitro only)
- Red yeast riceRice fermented with Monascus mould. Some products contain monacolin K, identical to lovastatin, so they act, and harm…HMG-CoA reductase (via monacolin K)
- GlucosamineAn amino sugar used by cartilage, sold for osteoarthritis. Evidence for knee pain is inconsistent; it may raise the…Cartilage glycosaminoglycan synthesis (substrate)
- Coenzyme Q10 (ubidecarenone)A mitochondrial electron carrier (ubiquinone) sold as a supplement. Statins lower its levels, yet it has not been…Mitochondrial electron transport chain (as its own carrier)
- Milk thistleA herbal supplement (silymarin) widely sold for the liver. Good trials have not shown that it helps liver disease.No established target (silymarin extract)
Others in the class
- Milk thistle
- Melatonin
- Black cohosh
- Chondroitin
Test yourself
Think of the answer, then tap the question to see it.
Through which receptor does St John's wort induce CYP3A4?
The pregnane X receptor (PXR), activated by hyperforin.
Which three supplements add to bleeding risk with warfarin?
Any three of: ginkgo, garlic, ginseng, glucosamine.
Which supplement contains the same molecule as lovastatin?
Red yeast rice (monacolin K).
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: St. John's Wort: Usefulness and Safety (National Center for Complementary and Integrative Health (NCCIH), 2025); Red Yeast Rice: What You Need To Know (National Center for Complementary and Integrative Health (NCCIH), 2022).
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Representative model, for educational purposes only.