Many Americans take dietary supplements along with prescription or over-the-counter medications. Sometimes the combination changes how a medication works. This page will not tell you which combinations are safe, because only your doctor or pharmacist can judge that for your situation. It gives you a short checklist of what to ask, based on what U.S. government health sources say.
1. Tell every provider about everything you take. Bring a written list of all the prescription and over-the-counter medications and supplements you take, how often you take each one, and the doses. You can also bring the bottles. Update the list at each visit [1].
2. Ask whether a supplement could make a medication stronger or weaker. The National Center for Complementary and Integrative Health (NCCIH, part of the NIH) explains that a supplement can increase a medication's effects and side effects, or decrease its effects. For example, glucosamine may increase the effects of blood thinners such as warfarin, which can raise the risk of serious bruising and bleeding [2]. St. John's wort is known to decrease the effects of many drugs, including antidepressants, birth control pills, some heart medications, warfarin, and certain statins [3].
3. Be extra careful with medications that have a narrow safety margin. NCCIH says interactions are of special concern for medications with a "narrow therapeutic range," where a level that is even a little too low or too high can cause serious reactions. Examples it lists include warfarin, digoxin, carbamazepine, phenytoin, and cyclosporine [4].
4. Do not forget over-the-counter medicines. Some supplements can interact with medicines sold without a prescription. NCCIH gives the example of black cohosh and St. John's wort supplements possibly interfering with the effectiveness of fexofenadine (Allegra), and notes that goldenseal, St. John's wort, kratom, and CBD may interact with many medications, including some sold without a prescription. If you plan to take both, ask your provider or a pharmacist [5].
5. Mention supplements before any surgery. Tell your surgeon and anesthesia provider about every supplement you take, as far in advance as possible. NCCIH says some supplements may affect your response to anesthetics, increase your risk of bleeding, or cause serious changes in heart rate or blood pressure, and some providers ask patients to stop herbal supplements several weeks before elective surgery [4].
6. If you are being treated for cancer or HIV, discuss every supplement with your provider. NCCIH reports growing concern that dietary and herbal supplements may interfere with the effectiveness of cancer and HIV treatments [1].
7. Read the label, but know its limits. The Supplement Facts panel lists a supplement's ingredients [6]. NCCIH says a label showing testing by an independent third party, such as the nonprofit U.S. Pharmacopeia (USP) or ConsumerLab.com, is one way to check that a product contains what is on the label [6]. Under U.S. law, supplement companies are responsible for evaluating the safety and labeling of their products before selling them [7]. The FDA can take action against adulterated or misbranded supplements only after the product is on the market, and NCCIH notes that supplements you buy from stores or online may differ in important ways from products tested in studies [8].
We are not a medical source, and we do not run clinical trials. This page cannot tell you whether a specific supplement is safe with a specific medication. Your doctor or pharmacist can, because they know your medications and your health history. This page does not recommend or link to any product.
Looking at a specific type of supplement? See our checklists for joint, prostate, memory, energy, and circulation supplements, or browse all guides.
Talk to your doctor or pharmacist before starting any supplement. The National Center for Complementary and Integrative Health (NCCIH) lists warfarin among medications with a narrow therapeutic range, where interactions are of special concern, and says glucosamine may increase the effects of blood thinners such as warfarin, which can raise the risk of serious bruising and bleeding.
Yes, it can. NCCIH says some supplements may decrease the effects of medications, so you may not get the full benefit your provider wants you to have. St. John's wort is known to decrease the effects of many drugs, including antidepressants, birth control pills, some heart medications, warfarin, and certain statins.
Some can. NCCIH gives the example of black cohosh and St. John's wort interfering with fexofenadine (Allegra), and notes that goldenseal, St. John's wort, kratom, and CBD may interact with many medications, including some sold without a prescription. If you plan to take both, ask your provider or a pharmacist.
A written list of all the prescription and over-the-counter medications and supplements you take, how often you take each one, and the doses. NCCIH also suggests you could bring the bottles, which can help your provider answer questions about the ingredients.
Yes, as far in advance as possible. NCCIH says some supplements may affect your response to anesthetics, increase your risk of bleeding, or cause serious changes in heart rate or blood pressure, and some providers ask patients to stop herbal supplements several weeks before elective surgery. Even if your surgery is an emergency, NCCIH says you or a loved one should still tell the surgeon and anesthesia provider about every supplement you take.
[1] NCCIH: How Medications and Supplements Can Interact - Talk With Your Health Care Providers.
[2] NCCIH: Some Supplements May Increase the Effects, and Side Effects, of Medications.
[3] NCCIH: Some Supplements May Decrease the Effects of Medications.
[4] NCCIH: Some Medication-Supplement Interactions Can Be Serious.
[5] NCCIH: Interactions With Over-the-Counter Medications.
[6] NCCIH: Tips on Reading Supplement Labels.
[7] U.S. Food and Drug Administration: Dietary Supplements (content current as of October 2024).
[8] NCCIH: Using Dietary Supplements Wisely (last updated January 2019).
Sources checked September 2026.