Dietary Supplements & Herbal Product Safety

Why every patient needs a supplement history

Regulation. Under the Dietary Supplement Health and Education Act (DSHEA, 1994), supplements are regulated as a category of food. They reach the market without FDA review of safety or efficacy, and the FDA must show that a product is unsafe or adulterated before it can remove it. Labels may make structure/function claims ("supports joint health") but not claims to diagnose, treat, cure, or prevent disease. A USP Verified or NSF seal confirms that the bottle contains what the label lists, not that the product works or is safe for a particular patient. Report suspected supplement adverse events to the FDA through MedWatch or the Safety Reporting Portal.

Ask explicitly. More than half of US adults take a supplement, and most will not mention it unless asked. At every medication reconciliation, ask about vitamins, herbals, teas, and weight-loss, bodybuilding, and sexual-enhancement products.

Adulteration. Some products contain undeclared prescription drugs: sildenafil or tadalafil analogs in "natural" sexual-enhancement products (profound hypotension with nitrates), sibutramine or laxatives in weight-loss products, and anabolic steroids in bodybuilding products. Some Ayurvedic and traditional remedies contain lead, mercury, or arsenic, and misidentified herbs containing aristolochic acid cause progressive interstitial nephropathy and upper-tract urothelial carcinoma.

St John's wort: the interaction heavyweight

Mechanism. Hyperforin, the herb's key constituent, activates the pregnane X receptor (PXR), which induces CYP3A4 (also CYP2C9 and CYP2C19) and intestinal P-glycoprotein. Substrates are metabolized and pumped out faster, so their levels fall. Induction builds and fades over roughly 1–2 weeks, which makes stopping the herb risky too: levels of drugs whose doses were raised during use (cyclosporine, warfarin) climb toward toxicity.

Serotonergic effects. The herb also inhibits serotonin reuptake. Combined with SSRIs, SNRIs, triptans, tramadol, linezolid, or MAOIs, it can cause serotonin syndrome: agitation, hyperthermia, diaphoresis, diarrhea, tremor, hyperreflexia, and inducible clonus (legs more than arms), in contrast to the lead-pipe rigidity of neuroleptic malignant syndrome. Hypericin causes photosensitivity.

Bleeding, liver, and cardiovascular hazards

Bleeding. Ginkgo (a platelet-activating factor antagonist), garlic, ginseng, and ginger (the "four Gs"), plus high-dose fish oil and vitamin E, impair platelet function. They add to the bleeding risk of warfarin, DOACs, aspirin, and clopidogrel, and ginkgo has been linked to spontaneous subdural hematoma. Dong quai contains coumarin-like compounds that raise the INR.

Stop these supplements about 2 weeks before elective surgery. PT/INR and platelet counts stay normal, so normal coagulation tests do not exclude the defect, and vitamin K does not reverse platelet dysfunction.

Liver injury. Kava, taken for anxiety, causes hepatitis that can progress to acute liver failure requiring transplantation, and it deepens sedation from benzodiazepines and alcohol. Concentrated green tea extract (epigallocatechin gallate, EGCG), common in weight-loss products, causes hepatocellular injury, whereas brewed green tea does not. Other culprits include anabolic steroids hidden in bodybuilding products (cholestasis) and comfrey, whose pyrrolizidine alkaloids cause sinusoidal obstruction syndrome. Jaundice with an INR ≥1.5 and encephalopathy defines acute liver failure: stop the product and involve a transplant center early.

Sympathomimetics. Ephedra (ma huang) contains ephedrine and pseudoephedrine, which release norepinephrine and stimulate adrenergic receptors, causing hypertension, tachyarrhythmias, myocardial infarction, stroke, seizures, psychosis, and sudden death. The FDA banned ephedrine-alkaloid supplements in 2004; substitutes such as bitter orange (synephrine) and large doses of caffeine carry similar risks.

Supplements that act like drugs or distort lab results

Red yeast rice. Its monacolin K is chemically identical to lovastatin, so it lowers LDL by inhibiting HMG-CoA reductase and carries statin toxicity: myalgia, myopathy, rhabdomyolysis, and transaminase elevation, made worse by CYP3A4 inhibitors such as clarithromycin, azole antifungals, and grapefruit. Monacolin content varies widely between products, and some batches contain citrinin, a nephrotoxic mycotoxin. A "statin-intolerant" patient who switches to red yeast rice has switched to an unregulated statin.

Licorice. Glycyrrhizin is metabolized to glycyrrhetinic acid, which inhibits renal 11β-hydroxysteroid dehydrogenase type 2. Cortisol is no longer inactivated to cortisone and occupies mineralocorticoid receptors, producing apparent mineralocorticoid excess: hypertension, hypokalemia, and metabolic alkalosis with low renin and low aldosterone. Treatment is stopping licorice (candy, teas, herbal remedies) and replacing potassium, adding spironolactone, eplerenone, or amiloride if needed. Deglycyrrhizinated licorice (DGL) does not cause the syndrome.

Vitamin A. Preformed vitamin A (retinol and retinyl esters) is teratogenic at high doses, so pregnant patients should keep it at or below 10,000 IU (3,000 μg) daily. The embryopathy resembles isotretinoin exposure: craniofacial and ear anomalies, conotruncal heart defects, and CNS and thymic defects. β-Carotene is not teratogenic because its conversion to retinol is regulated. Excess vitamin A also causes pseudotumor cerebri (headache, papilledema, CN VI palsy), dry skin, alopecia, bone pain, hypercalcemia, and hepatic fibrosis.

Biotin. Hair, skin, and nail products often contain 5–10 mg of biotin, and multiple sclerosis trials used far higher doses. Many immunoassays rely on streptavidin–biotin capture, so excess biotin in the sample distorts results in a direction set by the assay design.

A clinically euthyroid patient with "Graves' labs" who takes biotin needs no antithyroid drug: stop the biotin, wait a few days, and repeat the tests (or use a non-biotin assay).