How safe are dietary supplements? Here’s what you need to know

Plus, a list of popular herbs that can cause complications when taken with medication.

Photo by Kayla Maurais

By Sara Mukherjee, MD

Sara Mukherjee, MD, is a board-certified internal medicine physician with Mid-Atlantic Permanente Medical Group. She sees patients at the Kaiser Permanente Fair Oaks Medical Center.

Have you ever wondered how safe it is to take dietary supplements with prescription medications, but you’ve been wary of discussing your supplement use with your doctor?

You’re not alone. More than 72 million Americans who take prescription drugs also take supplements, according to the Centers for Disease Control and Prevention, but it’s estimated that fewer than one in five mention it to their health care providers.

Many patients are afraid we will disapprove, or perhaps even laugh at their use of supplements. But in my Washington, DC-area practice, I strive to develop a relationship with my patients so that they trust me and are comfortable discussing their use of alternative therapy, including supplements. Our job as doctors is not to judge, but to listen and learn, and help as we can.

What does worry me is that many people who take supplements seem to think of them as wholly benevolent—that they are natural and, therefore, safe. One patient came to me with a list of more than 70 supplements he was taking. Though there is a growing body of research about these products and their interactions, we don’t know nearly enough. Working with my clinical pharmacist, I discovered there was insufficient data, not only to assure the safety of taking this quantity of supplements, but to predict their potential interactions. So, it was almost impossible for me to treat this patient for his health issues while he was ingesting that many supplements.

The truth is that dietary supplements are medications, concentrated extracts of natural products which, when combined indiscriminately with prescription and even over-the-counter medicines, can lead to dangerous interactions. Some popular supplements are known to decrease the effects of the drugs you are taking, and others can increase the effects—including unwanted side effects.

I also worry about quality control. There is minimal regulation of dietary supplements, which are defined by law as products taken orally to supplement the diet that contain one or more dietary ingredients (vitamins, minerals or herbs, for example). Herbal supplements are a type of dietary supplement made from plants, algae and/or fungi. Sold as tablets, capsules, powders and teas, dietary supplements are regulated only for safety, not for whether they work. As to purity and truth in labeling, manufacturers are generally trusted to police themselves.

Here are just a few of the most popular herbs that can cause complications when taken with prescription and over-the-counter drugs, and even other supplements.

St. John’s Wort
One of the oldest natural treatments for depression, this herb can be dangerous when taken with any of a wide range of drugs, including some chemotherapy agents, heart and migraine medications, birth control pills, antidepressants, blood thinners and the vital anti-rejection drugs used after an organ transplant. St. John’s Wort is known for decreasing the effectiveness of more than 70 percent of all drugs, according to the National Center for Complementary and Integrative Health.

Widely used for colds, stomach upset and other conditions, goldenseal should not be used with any of the many medications broken down by the liver: the painkiller ibuprofen, the sedative diazepam and the chemotherapy drug tamoxifen are just a few examples.

A popular remedy for urinary tract infections, cranberry supplements should not be used with blood thinners such as warfarin and should be used cautiously with medications broken down by the liver.

Gingko Biloba
Many people take this ancient herb for memory issues, though studies have not found it to be effective in improving memory or slowing cognitive decline. It should not be taken with blood thinners or in the days or weeks leading up to elective surgery, because it may increase your risk of bleeding. It can also increase or decrease insulin levels in people with diabetes, and can interfere with medications broken down by the liver, including those used to prevent seizures.

One of the world’s most popular supplements, ginseng may support the immune system, lower blood sugar, improve mood and boost endurance. But people with diabetes should take it only under a doctor’s supervision, and it can interact with blood thinners, chemotherapy drugs, certain cholesterol- and blood pressure-lowering medications, and some antidepressants.

Often used to lower blood pressure and cholesterol and support the immune system, garlic is another supplement that does not mix well with blood thinners. It may also interfere with some HIV drugs, migraine medications, certain antidepressants and with drugs broken down by the liver. However, garlic supplements shouldn’t be confused with the amounts of garlic typically used to flavor cooking. Modest amounts of fresh, dried or powdered garlic typically used in cooking shouldn’t interfere with medications.

So, you should be wary of supplements if you are on blood thinners or blood pressure medication and other life-saving drugs. You should also stop using supplements several weeks before surgery to avoid interactions with anesthetics and to avoid increasing your risk of bleeding. If you must undergo emergency surgery, be sure to inform your surgeon and anesthesia provider about all the supplements you are taking.

Drug-herb interactions can be especially serious in the elderly and young children, and you should never take supplements or medications while pregnant or breastfeeding without your doctor’s approval.

Dietary supplements can be very helpful, but please consult your doctor (including your dentist, eye doctor or dermatologist) before taking them if you are using prescription medications.

There is a lot of good research out there; however, there is also a lot of hype and misinformation. Your doctors are here to help you make sense of it all.

To read more about how medications and supplements can interact, visit the website of the National Center for Complementary and Integrative Health.

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