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These 3 Supplements Are Trendy — But Do They Work?  

What you need to know about ashwagandha, berberine and bilberry

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It doesn’t take much — a scroll on social media or a stroll through the store — to come across an herbal pill, powder or gummy that claims to help with stress, sleep, weight loss and more.

You may have even tried one. Federal data shows that the majority of older adults take a dietary supplement — be it a vitamin, mineral or herbal supplement, sometimes called a botanical. But do these products really do what they claim?

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The promises aren’t always backed up by research, health experts say. “Unlike prescription drugs and over-the-counter drugs and everything else that is sold for our health, supplements can be promoted as if they work for these things [stress, sleep, weight loss, etc.], without any evidence from human clinical trials that they actually work,” 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. 

That’s because the Food and Drug Administration (FDA) does not approve supplements for their safety and effectiveness before they are marketed. Rather, the companies that make them are responsible for ensuring their products are safe and correctly labeled.

Here’s what you need to know about three trendy herbal supplements, including potential side effects and why you should always talk to a health care provider before taking one.

1. Ashwagandha

Ashwagandha is an evergreen shrub that grows in Asia and Africa. It’s been used for centuries to help manage stress and anxiety, and sometimes to improve athletic performance. These days, you can find the botanical in gummies, tinctures, bottled water, even mocktails.

What does the science say? Several studies have shown that ashwagandha can be effective at relieving stress, especially when taken orally, and it may even help with sleep and inflammation, though experts note that larger studies are needed. A small 2022 study from researchers at the University of Colorado found that participants who took ashwagandha reported an increased sense of well-being, better mental clarity and enhanced sleep quality.

Are there side effects? Reported side effects for the supplement include drowsiness, headache, stomach upset, nausea, diarrhea and vomiting. “However, evidence on the safety of longer term ashwagandha use over many months or years is lacking,” according to the National Institutes of Health’s (NIH) Office of Dietary Supplements. What’s more, the supplement may have potentially harmful effects on the liver and thyroid, the NIH says.  

Health experts caution against taking ashwagandha if you are pregnant or breastfeeding. People who have cancer, especially hormone-sensitive cancers, such as prostate cancer, should also avoid the supplement, since it can increase testosterone in the body. Research suggests that ashwagandha may interact with thyroid hormone medications, sedatives, immunosuppressants, and medications for diabetes and high blood pressure.  

2. Berberine

Sometimes called “nature’s Ozempic,” berberine has become a social media darling for its purported weight loss benefits. Berberine is a bitter-tasting chemical found in a variety of plants, including barberry and goldenseal. In supplement form, it’s often sold as a pill or powder.

What does the science say? A systematic review published in 2022 in the journal Frontiers in Nutrition found that berberine may hold some benefits for people with diabetes and other cardiovascular risk factors. Other studies have similarly found it can help people manage blood sugar levels and lower cholesterol. Evidence for weight loss, however, is thin so far, and many health experts say more research is needed.

“While some preliminary studies have suggested that berberine may play a role in losing weight, there haven’t been many clinical trials (studies conducted in people), so there isn’t enough rigorous scientific evidence to determine whether it is effective,” says the National Center for Complementary and Integrative Health (NCCIH).

Are there side effects? Common side effects include diarrhea, constipation, gas and upset stomach.

Be aware that berberine can interact with a number of medications. The supplement can affect how the body breaks down other drugs, potentially increasing their effects and side effects. Medications for diabetes, high blood pressure, blood clots, anxiety, sleep disorders and more all interact with berberine. It can also interact with other herbs and supplements, including cannabidiol (CBD) and probiotics.

According to the NCCIH, people who are pregnant or breastfeeding should not use berberine, and it should not be given to infants, as it can cause or worsen jaundice in infants and could lead to a type of brain damage called kernicterus.


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3. Bilberry

Bilberry — which comes from a bush native to northern areas of Europe and Asia, the northern United States and Canada — has been used to treat a variety of conditions since the Middle Ages, according to the NCCIH.

It’s considered high in antioxidant properties, so it is marketed to reduce inflammation, improve vision, and lower cholesterol or minimize cholesterol buildup in the blood vessels. 

What does the science say? A few studies suggest there are some health benefits to bilberry, “however these studies involved small numbers of people,” the NCCIH says, meaning more research is needed to confirm any findings. For example, a clinical trial of 24 adults, published in 2015, found that consuming bilberries helped to reduce gum inflammation and bleeding. Another 2015 study out of Japan found that bilberry extract helped with eye fatigue.

Little scientific evidence is available, and many more studies are needed to support bilberry’s use for cholesterol and inflammation.

Are there side effects? Short-term use is generally safe, the NCCIH says, however bilberry leaves may be unsafe when taken orally in high doses or for long periods of time, the center warns.

What’s more, bilberry may interact with the cancer drug erlotinib, used to treat some lung and pancreatic cancers. It can also interact with diabetes drugs and medications that slow blood clotting.

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Supplement shopping? 3 things to keep in mind

Because of the lack of strong evidence, Cohen says he usually doesn’t recommend to his patients that they take one of these supplements. However, if a patient wants to try them, he suggests they look for a few things when making their selection. “Because it absolutely is the case that if you want to try these supplements, you might be getting a subpar product or even a product contaminated with other ingredients that are not on the label,” Cohen says.

To avoid that scenario, he says:

1. Don’t buy combination products. “I recommend buying a supplement that only lists that one botanical on the label,” Cohen says.

2. Avoid supplements littered with claims on the packaging. “In the past, what we’ve seen is sometimes the claims, like weight loss claims, end up leading the manufacturer to spike the products with unproven, untested, unapproved drugs, in an effort to meet the consumer expectations,” Cohen says. (Remember: Supplements and their claims do not have to be approved by the FDA before they hit store shelves.)

3. Look for supplements that have been reviewed by a high-quality, third-party program, like NSF or US Pharmacopeia. Cohen says these programs evaluate the production and manufacturing of the supplement, and they make sure what’s on the label is in the bottle. “There’s extremely low entry to the marketplace,” he says. “That’s why we need additional third-party information to confirm that these are high-quality products.”

One other tip: Talk to your health care provider before starting any new product, even if it’s an over-the-counter one. Your doctor can help you identify any potential medication interactions or side effects.

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