6 supplements that don’t always mix well with prescriptions

Yet federal research shows that about 34% of survey participants — representing about 72 million people in the United States — take some kind of dietary supplement along with a prescription drug.

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

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 many drug interactions and can reduce the potency of birth control pills and hormone replacement therapy, says Shane-McWhorter. It may also interfere with omeprazole (Prilosec), alprazolam (Xanax), some statins and some antihistamines, reports the Mayo Clinic.

Additionally, St. John’s Wort may render Pfizer’s new COVID-19 antiviral treatment, Paxlovid, ineffective. “If a person is being treated with Paxlovid and taking St. John’s Wort, that basically means the Paxlovid may not work,” says Shane-McWhorter.


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

In supplement form, it is taken as capsules, tablets, and syrups for many conditions, including heart disease, diabetes, and migraine. But CoQ10 can also interfere with the ability of blood thinners to do their job of preventing blood clots from forming. As a result, “people could get a punctured blood clot,” says Shane-McWhorter.

3. Turmeric

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

Ginkgo biloba (a 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 a blood thinner can increase the effect.

Cooking with turmeric? It’s still good to use in the kitchen, says Shane-McWhorter. “When the products are used as food, we don’t think that’s really a problem,” she adds.

4. Probiotics

Filled with 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 prescription drug’s effectiveness, Shane-McWhorter says.

5. Vitamin C

Vitamin C is naturally present in citrus fruits, strawberries, broccoli and tomatoes, among other foods. It is also taken as a supplement for a myriad of reasons, ranging from cold prevention to cancer prevention.

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

6. Milk Thistle

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

Bottom Line: Talk to Your Doctor

Ideally, to stay out of trouble, patients would tell their doctor about the supplements they take. But those conversations don’t happen as often as they should, says Derjung Mimi Tarn, MD, professor of family medicine at the University of California, Los Angeles.

A 2015 study by Tarn and colleagues found that less than 50% of patients disclose dietary supplement use, and even among those who do, only about a third of the supplements taken are mentioned to doctors.

One reason for the disconnect: Patients may not realize that over-the-counter herbs or extra vitamins they incorporate into their daily pile of pills count as anything to discuss with a doctor, so they omit from the list when asked by their supplier, explains Shane-McWhorter. It is also not uncommon for consumers to confuse “natural” with “safe” and not fully recognize the potency of some of these products.

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

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