9 Dangerous Supplement Combinations You Should Avoid

vm / Getty Images

With age and new (or more) chronic health conditions, it's common for people to need prescription medications. Many people also use over-the-counter products and supplements to meet their health needs.

Experts say that taking certain medicines and supplements at the same time could have dangerous, even life-threatening, consequences. Moreover, many people combine supplements and prescription or over-the-counter (OTC) medications without knowing the potential interactions.

Some medication combos may lead to diminished drug effectiveness, increased risk of drug toxicity, and unexpected side effects.

Taking vitamin B6 with levodopa, a medication for Parkinson’s disease, can reduce the medication’s effectiveness. However, some levodopa medications also contain carbidopa, which can counteract the interaction.

People using levodopa or levodopa-carbidopa intestinal gel (LCIG) can develop a vitamin B6 deficiency. This can cause anemia, depression, neuropathy, and other issues. A healthcare provider may monitor you and advise you on B6 supplementation. It’s OK to take vitamin B6 if you’re on LCIG under your healthcare provider’s advisement.

Vitamin K can counteract the effects of blood-thinning medications like warfarin, possibly making them less effective.

If you’re on blood-thinning medications, talk with your provider before taking vitamin K supplements or increasing your dietary intake of vitamin K.

Certain supplements like iron and calcium can interfere with the absorption of thyroid hormone replacement medications like levothyroxine.

Taking these supplements and thyroid hormone replacement medications at least four hours apart is best.

Vitamin C increases the absorption of aluminum from antacids, medicines like Tums, that neutralize stomach acid and help relieve heartburn or indigestion.

However, taking vitamin C and antacids together can lead to toxic levels of aluminum in the body. Therefore, they should be taken at least two hours apart.

Vitamin E can increase the risk of bleeding when it’s taken with blood-thinning medications like warfarin.

If you are taking a blood thinner, ask your provider before taking vitamin E.

St. John’s Wort supplements can interact with many medications, including antidepressants, birth control pills, and blood thinners.

St. John’s Wort can reduce the effectiveness of these medications, and mixing them can cause harmful effects.

Goldenseal supplements can interact with some medications, including clotting medicines. The interaction may reduce the body’s ability to clot, leading to bleeding or bruising.

Given the seriousness of the interaction, it’s often recommended to avoid using goldenseal and blood clotting medications together.

Ginkgo biloba supplements can also increase the risk of bleeding when taken with blood-thinning medications like warfarin or aspirin.

Supplements containing licorice root can interact with diuretics and blood pressure medications, making their side effects worse or even causing serious problems, such as potassium imbalances or blood pressure fluctuations.

If you’re taking a prescription medication and thinking about trying a supplement, talk to your provider or pharmacist.

If you are prescribed medications and plan on using supplements, timing is everything. For example, Marilyn Tan, MD, double board certified in endocrinology and internal medicine and a clinical associate professor of medicine at Stanford University School of Medicine, said that thyroid hormone medications should be taken on an empty stomach and separated from supplements by at least four hours—especially if they contain calcium and iron.

“Other endocrine medications like the osteoporosis medication Fosamax and the diabetes medication Rybelsus need to be taken on an empty stomach and separated from other medications by at least 30 minutes,” Tan added.

Danielle Crumble Smith, RDN, a certified registered dietitian at Top Nutrition Coaching, recommends discussing timing your doses with your provider to avoid potential interactions. As a general rule, space out when taking supplements and your medications by at least two hours.

Your healthcare provider can guide you on what combinations to avoid and how to use supplements with medications safely.

In general, it’s never a bad idea to let your provider know if you’re thinking about trying something new since you may not know about the possible risks involved.

“Supplements seem harmless, but it is important to consult a healthcare professional if you are considering starting a new supplement,” Crumble Smith said. “This is particularly true if you are currently taking medications.”

When picking up your medications, you can also ask your pharmacist about drug-supplement combinations. Pharmacists are trained to know about drug interactions, including those that can happen with dietary supplements. They also have access to comprehensive databases and tools that let them check for potential interactions.

A pharmacist can advise you on how to use supplements safely, check for interactions, make suggestions about the timing of your doses, or offer alternatives. In some cases, a pharmacist might be able to suggest dose adjustments that could help you avoid an interaction.

Crumble Smith said it’s essential to give a pharmacist a complete list of everything you’re taking, from prescription meds to OTC products and supplements, as this information will help them make the most accurate assessment.

There are also several databases and online tools from reputable resources that you can use to check for potential drug and supplement interactions on your own, including:

Crumble Smith said that while these resources can provide helpful information, they are not a substitute for professional medical advice.

“Always consult with a healthcare provider or pharmacist before starting, stopping, or modifying your medication or supplement regimen,” she said.

If you’re taking prescription medications, know that using a supplement along with it may not be as harmless as you might think. Some medications and supplements can have serious, even life-threatening, interactions.

Always ask your healthcare provider before you start a supplement, especially if you’re taking any medications. If you have questions about your medications or how to use supplements safely, talk to your provider or pharmacist.

Health Policy Institute. Prescription drugs.

Food and Drug Administration. Mixing medications and dietary supplements can endanger your health.

National Center for Complementary and Integrative Health. Using dietary supplements wisely.

Agnieszka W, Paweł P, Małgorzata K. How to optimize the effectiveness and safety of Parkinson's disease therapy?—A systematic review of drugs interactions with food and dietary supplements. Curr Neuropharmacol. 2022;20(7):1427-1447. doi:10.2174/1570159X19666211116142806

Pengo V, Denas G. Optimizing quality care for the oral vitamin K antagonists (VKAs). Hematology Am Soc Hematol Educ Program. 2018;2018(1):332-338. doi:10.1182/asheducation-2018.1.332

MedlinePlus. Levothyroxine.

MedlinePlus. Taking antacids.

Icahn School of Medicine at Mount Sinai. Vitamin C (ascorbic acid).

Icahn School of Medicine at Mount Sinai. Vitamin E.

Icahn School of Medicine at Mount Sinai. St. John’s wort.

Icahn School of Medicine at Mount Sinai. Goldenseal.

Icahn School of Medicine at Mount Sinai. Ginkgo biloba.

Icahn School of Medicine at Mount Sinai. Licorice.

By Alyssa Hui-AndersonHui-Anderson is a health news writer and former TV news reporter. She was the 2020 recipient of the Midwest Broadcast Journalists Association Jack Shelley Award.