Can supplements interact with prescription medicines?

Yes. St. John's Wort, vitamin K, calcium and iron, fish oil, ginkgo, and potassium can all interact with common prescriptions. Always tell your pharmacist about every supplement you take.

Which supplement interacts with the most medicines?

St. John's Wort is a notable one — it can lower the levels of many medicines including some antidepressants, birth control, blood thinners, and transplant drugs, and add serotonin risk.

Home › Guides › Do supplements interact with prescription drugs?

Do supplements interact with prescription drugs?

By the RxSafeCheck team · Educational, reviewed for plain-language clarity · Morning Mind LLC

"Natural" doesn't mean "no interactions." Vitamins, minerals, and herbal supplements can change how prescription medicines work — sometimes significantly. Here's what to know.

Common supplements that can interact

St. John's Wort — can lower the levels of many medicines (some antidepressants, birth control, blood thinners, transplant drugs) and raise serotonin risk.
Vitamin K (and leafy greens) — can counteract warfarin; consistency matters.
Calcium, iron, magnesium, zinc — can block absorption of some antibiotics and thyroid medicine if taken together.
Fish oil, vitamin E, ginkgo — may add to bleeding risk with blood thinners.
Potassium — can add up with certain blood pressure medicines.

Tell your pharmacist everything: Include every vitamin and herbal product on your medicine list. Supplements are a common blind spot because people don't think of them as "drugs."

The takeaway

Before adding a supplement, check it against your medicines and ask your pharmacist. RxSafeCheck lets you add supplements and food factors alongside prescriptions to see possible interactions.

Check your own medicines free

See how your prescriptions, supplements, and food may interact — organized by the part of the body they affect.

Open the medication tool →

Important: This article is educational and not medical advice. It does not replace your pharmacist or prescriber. Always confirm decisions about your medicines with a qualified professional, and call your local emergency number for emergencies. In the U.S., Poison Control is 1-800-222-1222.