It's Tricky to Know Which Supplements Are Safe — Here's What to Avoid

Not all vitamins and supplements are safe. Pieter Cohen, associate professor from Harvard Medical School warns to keep an eye out for these potentially problematic classes of supplements.

By Sean Mowbray; Medically Reviewed by Dr. Ahmad Talha Azam
Mar 28, 2024 6:00 PM
woman looking doubtful about supplements
(Credit: fizkes/Shutterstock)


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Social media is rife with recommendations to consume one supplement or the other. Promising to fill you with energy, enhance your memory, or more, these pills, tablets, drinks, and more can often stand on shaky scientific ground. Knowing which supplement is safe to take is essential.

Vast amounts of supplements are consumed each year; one 2022 survey found that 75 percent of Americans take them, most on a regular basis. That means the industry rakes in billions each year. In the U.S., vitamin and supplement manufacturers revenue topped $40 billion in 2023. Yet, experts warn this booming sector lacks both regulation and oversight.

How To Know If Supplements Are Right For You

Medical experts recommend consulting professionals as a first port of call to discuss specific needs and concerns prior to taking a supplement. This can also help assess whether a supplement is actually necessary through blood tests, if possible. For vitamins and minerals, for example, other steps can include evaluating your diet to ensure you are consuming adequate amounts of nutrient-rich foods.

Though multivitamins and mineral supplements are generally safe, over consuming them can come with potential complications. Consuming too much Vitamin A, for example, is associated with multiple health issues such as dizziness, hair loss, headaches, and more. Other supplements can also clash with the use of prescription medicines.

Multivitamins and mineral supplements are generally safe and are recommended for certain groups of people, according to Pieter Cohen, associate professor at Harvard Medical School and an internist at Cambridge Health Alliance.

“For a healthy person, you don’t need to take multivitamins,” Cohen says. “There’s no evidence that it will help you prevent cancer, heart disease, or stroke.”

What Are Problematic Classes of Supplements

For other categories of supplements, however, the picture is more complex. Cohen explains that others, such as botanicals, weight loss, sports, sexual performance, or cognitive enhancement supplements, are amongst the problematic classes out there.

“Those are some of the categories that jump up highly on my list of things that are more likely to be contaminated with or adulterated with drugs or experimental substances,” he says.

Read More: Tumeric and 9 Other Botanical Supplements Can Boost Your Health

Research conducted by his team at the Supplement Research Programme has flagged multiple issues with these kinds of supplements, including some that contain far less or more of the stated ingredients, as well as potentially harmful substances or experimental drugs. Tests on melatonin gummy supplements — widely taken to improve sleep quality and stress — for example, found that some contained none of the ingredients or up to 347 percent more than stated on the bottle.

“Another problem that we see is that what's in the bottle is often different than what's on the label,” Cohen says. In the melatonin study, multiple products contained heightened levels of cannabidiol or CBD. “Sometimes what's in the bottle can be very worrisome.”

In the first instance, he states that weight loss, sexual performance, and cognitive performance supplements should be avoided, given often scarce evidence that they have any beneficial impact.

“The other recommendation is to avoid any supplement that has health claims on the bottle,” Cohen adds. “These health claims do not need to be supported by evidence in human trials. In other words, it can say things like this will improve your cognition or improve your memory, even if there's no study that's ever shown that the supplement will actually help you do that.”

Read More: The Only Gains You'll Get From SARMS are a List of Health Issues

Choosing The Right Supplements 

Most importantly, he advises selecting supplements from reputable brands with third-party certification. This means those certified by bodies such as the National Institutes of Health, U.S. Pharmacopeia, or NSF International.

“If it has an NSF or a USP stamp on the label, then you can be assured that what's in the supplement is accurately labeled, and what’s on the label is what's in the bottle,” Cohen states.

In addition, buying supplements that contain only one ingredient whenever possible is recommended. “There’s some common exceptions like multivitamins and calcium plus vitamin D,” Cohen says. “But in general, the safest way to buy supplements is to look for those that list just that one ingredient you are looking for on the bottle, not one that’s mixed with a lot of other stuff.”

“When it’s also third-party certified, that’s the most likely way of getting what you think you are in the bottle,” he concludes. Following these tips and recommendations can help you navigate the multitude of supplements out there, but the question of whether they are necessary should always be asked first and ideally discussed with a health professional.

This article is not offering medical advice and should be used for informational purposes only.

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