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6 Supplements That Don’t Always Mix With Prescription Drugs

Over-the-counter vitamins, herbs and minerals aren’t without potential risks

bottles of supplements with a woman's hand nearby, counting the pills

Johner Images / Getty Images

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Turmeric, ginseng, a probiotic, even vitamin C — all of these, when taken in packaged form, are supplements. Some have lined store shelves for decades. Others are ancient cures processed and packaged for 21st-century consumers.

Whatever their history, supplements are everywhere these days, and consumers are eating them up, spending billions each year on capsules, powders and gummies. More than half of adults age 20 and older have taken one in the last 30 days, data from the National Health and Nutrition Examination Survey found — and that percentage increases with age. About 80 percent of women over age 60 take dietary supplements, the same report shows.

But what many adults don’t realize is that taking some of these supplements alongside prescription drugs and other medicines can have dangerous and even life-threatening effects. A number of supplements can enhance, diminish or negate a prescription drug in ways that can be consequential and unpredictable, says Laura Shane-McWhorter, a clinical professor of pharmacology at the University of Utah.

Still, federal research shows about 34 percent of survey participants — representing roughly 72 million people in the United States — take some kind of dietary supplement along with a prescription medication.

Wondering which supplement-prescription pairings can be risky? Here are six popular supplements and their known effects on some common medications.

1. St. John’s wort

Derived from a flowering shrub native to Europe, St. John’s wort is often taken to treat mild to moderate depression, or to reduce menopausal symptoms such as hot flashes. But it has numerous drug interactions and can reduce the potency of birth control pills and hormone replacement therapy, Shane-McWhorter says. It can also interfere with omeprazole (Prilosec), alprazolam (Xanax), certain statins and some antihistamines, Mayo Clinic reports.

What’s more, St. John’s wort can render Pfizer’s new COVID-19 antiviral treatment, Paxlovid, powerless. “If a person is being treated with Paxlovid and is taking St. John’s wort, that means essentially that the Paxlovid may not work,” Shane-McWhorter says.

2. CoQ10

Coenzyme Q10 (CoQ10) is an antioxidant produced by our bodies to promote cell growth and maintenance; the levels of it in our body can decrease as we age.

In supplement form, it’s taken by way of capsules, tablets and syrups for numerous conditions, including heart disease, diabetes and migraine. But CoQ10 can also interfere with the ability of blood thinners to do their job, which is to prevent blood clots from forming. As a result, “people could have a breakthrough blood clot,” Shane-McWhorter says.

3. Turmeric

The ancient spice has been shown to have many health benefits, from improving memory to lowering inflammation and even decreasing the risk of heart disease. It also has anticoagulant effects, which means you don’t want to mix turmeric supplements with a blood thinner or even, possibly, aspirin, due to the risk of internal bleeding, Shane-McWhorter says.

Ginkgo biloba (an herb) and vitamin E are two other dietary supplements that can thin the blood, according to the Food and Drug Administration. So taking them with an anticoagulant can augment the effect. 

Cooking with turmeric? It’s still fine to use in the kitchen, Shane-McWhorter says. “When products are used as foods, we don’t think it’s that much of an issue at all,” she adds.

4. Probiotics

Full of beneficial bacteria, probiotics are often taken to aid digestion and improve gut health. But don’t take one within two hours of taking an antibiotic, or you could reduce the effectiveness of the prescription medication, Shane-McWhorter says.

5. Vitamin C

Vitamin C occurs naturally in citrus fruits, strawberries, broccoli and tomatoes, among other foods. It’s also consumed as a supplement for a myriad of reasons, ranging from warding off the common cold to preventing cancer.

But high-dose vitamin C supplements may reduce the effectiveness of some types of cancer chemotherapy, says Courtney Rhodes, a spokeswoman for the FDA. It can also interfere with niacin and statins and affect estrogen levels, according to Mayo Clinic.

6. Milk thistle

A flowering plant related to daisies, milk thistle is taken as a supplement to promote liver and heart health. It may also lower blood sugar, which could be a concern for someone who’s on diabetes medication. When combined with insulin, it can be “like taking a little bit too much” glucose-lowering medication, Shane-McWhorter says.

Bottom line: Talk to your doctor

Ideally, to head off trouble, patients would be talking to their doctors about the supplements they are taking. But these conversations don’t happen as often as they should, says Derjung Mimi Tarn, M.D., a professor of family medicine at University of California, Los Angeles.

study led by Tarn and her colleagues in 2015 found that fewer than 50 percent of patients disclose the use of dietary supplements, and even among those who do, only about one-third of the supplements taken are mentioned to doctors.

One reason for the disconnect: Patients may not realize the over-the-counter herbs or extra vitamins they’re working into their daily pile of pills count as anything that needs to be discussed with a doctor, so they leave them off the list when their provider asks, Shane-McWhorter explains. It’s also not uncommon for consumers to confuse “natural” with “safe” and fail to fully recognize the potency of some of these products.

To help avoid any health hazards that can arise from mixing supplements and medications, it’s important to ask your doctor about possible adverse reactions before starting any new medication or supplement, Tarn says. “Greater awareness of the importance of discussing supplement use is needed in both providers and patients,” she adds.


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The FDA suggests bringing a list of everything you take — over-the-counter medicines (pain pills, allergy relief, etc.), dietary supplements and prescription drugs — with you to your next routine appointment to make sure your information is up to date. And be sure to keep track of the dosages and how many times a day you take them.

Also, if you’re planning a surgery, don’t be surprised if your doctor asks you to stop taking dietary supplements two or three weeks before the procedure to avoid changes in heart rate, blood pressure or bleeding risk.

Interested in learning more? The National Institutes of Health has a database where you can search for a supplement and find links to verified sources with information about the product and its interactions. And Herbs at a Glance is an alphabetical listing of herbs and botanicals, with information on their uses and safety concerns, from the National Center for Complementary and Integrative Health, a division of the NIH.

For those willing to pay, Shane-McWhorter recommends the Natural Medicines database, where subscribers can use the interaction checker and the effectiveness checker to learn more about particular supplements.