Top 10 Supplement-Drug Interactions That Send People to the ER

An estimated 23,000 emergency department visits each year in the US are attributed to dietary supplement adverse events, per Geller et al. in NEJM. A meaningful fraction of those involve interactions with prescription drugs the patient was already taking. The combinations below have the highest documented frequency or severity of acute clinical consequences — bleeding, serotonin syndrome, hypoglycemic crisis, hepatotoxicity, or drug-level shifts that destabilize otherwise controlled disease. Each entry lists the mechanism and the magnitude of clinical risk.

1. 1. St. John's Wort + SSRIs / SNRIs / Triptans → Serotonin Syndrome. St. John's Wort is a serotonergic agent; combined with serotonergic antidepressants or migraine triptans it can precipitate serotonin syndrome (hyperthermia, clonus, autonomic instability). Multiple ER case reports. St. John's Wort is also a strong CYP3A4 inducer that lowers levels of oral contraceptives, cyclosporine, warfarin, and antiretrovirals. See our St. John's Wort interaction piece.
2. 2. Ginkgo + Warfarin / DOACs / Antiplatelet → Major Bleeding. Ginkgo has antiplatelet activity via PAF-receptor antagonism. Case reports of spontaneous subdural hematoma in ginkgo users on anticoagulants. Stop ginkgo 1–2 weeks before any surgery and avoid in adults on warfarin, apixaban, rivaroxaban, aspirin, or clopidogrel. See our ginkgo review.
3. 3. Garlic Supplements + Saquinavir / Anti-HIV ART → Subtherapeutic Drug Levels. High-dose garlic supplements (not garlic in food) reduce saquinavir plasma levels by ~50%, with documented antiretroviral therapy failure. Same induction mechanism affects cyclosporine and tacrolimus levels in transplant patients. See our top supplement interactions piece.
4. 4. Vitamin K Supplements + Warfarin → INR Destabilization. Even modest changes in vitamin K intake (50–100 mcg daily) can swing the INR of a warfarin-stabilized patient. Patients should avoid starting or stopping vitamin K1 or K2 supplements without anticoagulation team input. The reverse case — patients on warfarin starting K2 for bone — destabilizes anticoagulation. See our K2 review.
5. 5. Berberine + Metformin or Sulfonylureas → Hypoglycemia. Berberine and metformin both lower fasting glucose via AMPK activation; the combination can produce additive hypoglycemia. Sulfonylureas + berberine has been associated with hospital admissions for symptomatic hypoglycemia. Berberine also inhibits CYP3A4 and P-glycoprotein, affecting drug levels broadly. See our hypoglycemia interaction piece.
6. 6. Green Tea Extract (High-Dose) + Acetaminophen + Statins → Hepatotoxicity. High-dose EGCG products have produced acute hepatitis case reports, with risk amplified by concurrent acetaminophen or statin use. The 2022 USP Verified withdrawal of green tea extract from its monograph review reflects this. See our green tea hepatotoxicity piece.
7. 7. Yohimbe + MAOIs / Stimulants → Hypertensive Crisis. Yohimbine is an alpha-2 antagonist; combined with MAOIs, stimulants, or even decongestants it can produce hypertensive emergency. Yohimbe-containing pre-workouts and "male enhancement" supplements are over-represented in supplement-related ED visits. See our yohimbe piece.
8. 8. Kava + Acetaminophen / Alcohol / Benzodiazepines → Liver Failure + Sedation. Kava hepatotoxicity led to bans in several European countries. Combined with hepatotoxic drugs or alcohol, the risk multiplies; combined with benzodiazepines, additive CNS depression has been reported. The CDC documented a sharp rise in kava-related poison control calls — see our CDC kava piece.
9. 9. Potassium Supplements + ACE Inhibitors / ARBs / Spironolactone → Hyperkalemia. ACE inhibitors, ARBs, and aldosterone antagonists all raise serum potassium. Adding potassium chloride or citrate supplements (including "salt substitutes" with potassium chloride) on top can produce arrhythmia-grade hyperkalemia. Cases of cardiac arrest documented. Co-prescription of supplements is poorly captured in medication reconciliation.
10. 10. High-Dose Fish Oil (≥4 g/day) + Antiplatelets / Anticoagulants → Bleeding + Atrial Fibrillation. The REDUCE-IT and STRENGTH trials both showed a small but real increase in atrial fibrillation incidence with high-dose omega-3. Combined with antiplatelets, the bleeding risk is additive. The 2021 AHA statement specifically cautioned about this combination in adults with prior afib. See general supplement-medication interaction guidance and our atrial fibrillation condition page.

How to Use This List Practically

If you take any prescription medication, share your full supplement list — including occasional or PRN use — with your physician and pharmacist. Many ER visits in the literature involve supplements the patient never mentioned to their clinician because "they're just vitamins." Online drug-interaction checkers (Lexicomp, Medscape) include many but not all supplement entries; the absence of a flagged interaction is not a guarantee of safety. The American Society of Anesthesiologists recommends stopping all herbal supplements 1–2 weeks before surgery for this reason.

Bottom Line

The supplement industry markets these products as inherently safe because they are "natural." The reality is that herbal and high-dose vitamin products contain pharmacologically active compounds that interact with prescription drugs in clinically significant ways. The combinations above are the most-documented ER scenarios but the underlying lesson is broader: any supplement that produces a clinically meaningful effect can produce a clinically meaningful interaction.