6 Supplements That Don’t Always Mix With Prescriptions

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.

A 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.