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Dietary Supplements and Side Effects

Natural doesn’t always mean safe, so check with your doctor before popping a pill

Dietary supplements can have harmful side effects.
BSIP / Getty Images

It’s common knowledge that prescription drugs can cause side effects — TV ads don’t let you forget that. And plenty of people know that taking over-the-counter medication can lead to unwanted symptoms (think of how some antihistamines can make you sleepy).

When it comes to dietary supplements, however, many consumers are unaware that their vial of vitamins or bottle of herbs and other botanicals (think echinacea and ginkgo biloba) could come with risks. And a big reason boils down to how they’re sold — “as openly and as freely as food,” says Pieter Cohen, M.D., an internist at Cambridge Health Alliance and an associate professor of medicine at Harvard Medical School who studies supplement safety.  

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“So just like you can buy some broccoli or a can of tomato sauce, you can just buy whatever sort of supplements or botanicals or probiotics you want in the store,” he says. And this helps to create a "false impression" that the powders, pills and capsules can’t cause harm.

But a 2015 study, published in the New England Journal of Medicine, found that about 23,000 people wind up in the emergency room each year due to adverse events caused by dietary supplements. Reactions the researchers identified ranged from chest pain and heart palpitations to dizziness and vomiting, and adults 65 and older were more likely to be hospitalized because of them.

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Rashes, shortness of breath, diarrhea, severe joint or muscle pain, slurred speech and blood in the urine are other possible adverse events that can result from supplement use, according to the U.S. Food and Drug Administration (FDA). These symptoms can vary from less serious to life-threatening.

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Did You Know?

Fresh fruits and veggies are packed with vitamins and minerals, but manufacturers also add them to everyday foods, like breakfast cereals and beverages. So you may be getting more nutrients than you think through your diet, and taking more than you need raises the risk of side effects.

Source: National Institutes of Health Office of Dietary Supplements

How supplements can cause side effects

How can a vitamin or plant product cause adverse reactions typically associated with powerful drugs? Reasons run the gamut, experts say.

Supplements, which are not held to the same federal approval standards as over-the-counter and prescription drugs, despite their widespread use, contain active ingredients that can have strong effects on the body, the National Institutes of Health’s (NIH) Office of Dietary Supplements explains. And in some products, these ingredients can be particularly potent.

Cohen points to red yeast rice as an example — it’s a traditional Chinese culinary and medicinal product that’s “been used for hundreds of years to treat a variety of problems.” In the U.S., supplements containing red yeast rice are often marketed as effective at lowering cholesterol, and that’s because some red yeast rice products contain a substance produced by the yeast that is “chemically identical to the active ingredient in the cholesterol-lowering drug lovastatin,” the NIH’s National Center for Complementary and Integrative Health says.

Some supplements contain no or low levels of this substance (known as monacolin K), but others are formulated “more like a prescription drug,” Cohen says. In turn, they can cause the same types of side effects and drug interactions as lovastatin, like muscle pain and weakness and liver toxicity, according to the NIH. And often consumers have no way of knowing how much of this prescription-like substance is present in a supplement. 

Supplements can also interact with other drugs in dangerous ways. Vitamin K can hamper the effectiveness of blood thinners, while vitamin E can augment their power, increasing the risk of bleeding. And Saint-John’s-wort can weaken the effects of some heart medications, antidepressants and statins.

Older adults need to be especially careful when it comes to possible interactions such as these, Cohen warns, since “many people who are over 65 are taking prescription medications.” In fact, more than 4 in 10 adults 65 and older take at least five prescription drugs a day, and nearly 20 percent take 10 or more, according to a Lown Institute report.

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Most-Used Natural Products by U.S. Adults

1. Fish oil/omega 3/DHA, EPA fatty acids
2. Glucosamine and/or chondroitin
3. Probiotics/prebiotics
4. Melatonin
5. Coenzyme Q10
6. Echinacea
7. Cranberry (pills or capsules)
8. Garlic supplements
9. Ginseng
10. Ginkgo biloba

Source: National Center for Complementary and Integrative Health/NIH

What’s more, older people don’t metabolize compounds found in drugs and supplements as efficiently as their younger peers. “So taking excessive supplements can certainly lead to more problems in someone [who has a harder time] getting it out of their system, because the kidneys are not functioning like they would in a 20- or 30-year-old,” he explains.

In some instances, the FDA has identified supplements containing prescription drugs and other active ingredients not listed on the label, ratcheting up the risk for additional side effects and reactions. A study published in JAMA Network found that pharmaceutical ingredients were identified in 776 dietary supplements between 2007 and 2016. Most were marketed for sexual enhancement, weight loss or muscle building.

Be a savvy consumer

The guidance from experts isn’t to avoid supplements entirely but to exercise caution when using them. “These products are health products and should be considered just like over-the-counter medications,” Cohen says. “We know that we have to be careful with [drugs like aspirin and Motrin]. And supplements should be treated the same way.”

His advice: If you’re interested in starting a supplement, step back and think about why you want to take it, and then bring that concern to your doctor. “We actually know that going out and taking a multivitamin just for general health — to prevent heart disease, cancer, you name it — doesn’t work,” he says. So ask your physician if you have a health issue that can be alleviated with a vitamin, mineral or other product. (You can also check out the FDA’s new Supplement Your Knowledge initiative for a list of other questions to bring up with a health care provider regarding supplement use.)

If you are already taking a supplement — and more than half of Americans are — it’s important to let your doctor know, says Cara Welch, director of the FDA’s Office of Dietary Supplement Programs in the Center for Food Safety and Applied Nutrition. Keep a record of what you are taking and how often. Or, better yet, bring the bottles to your next appointment so your doctor can take a look “and adjust accordingly, based on what they know about the patient,” Welch says.

If a supplement is recommended, look for one that has a stamp from NSF International or U.S. Pharmacopeia, Cohen suggests. These third-party groups test supplements and verify that they contain the ingredients listed on the label and that they aren’t tainted with harmful substances. And remember that a supplement “should not claim to treat, cure or prevent disease,” Welch says. If you see one that does, that’s a red flag.

Finally, if you experience side effects or a bad reaction after taking a supplement, stop taking the product and report it to the FDA. “We have physicians that review every single one of those adverse-event reports to see if they indicate an issue with a particular product or a particular ingredient,” Welch says.

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