I'm a Doctor and Beg You Never Take This Vitamin

There seems to be a vitamin for everything these days, from immune health to sexual dysfunction—but it can be difficult to know which ones work (or are at best harmless), and which might actually be dangerous. "The bottom line is that there is absolutely no substitute for a well-balanced diet, which is the ideal source of the vitamins and minerals we need," says Monique Tello, MD, MPH. "…Our bodies prefer naturally occurring sources of vitamins and minerals. We absorb these better. And because commercially available vitamins, minerals, herbs, etc. are lumped together as 'supplements,' the FDA doesn't regulate them. When we ingest processed, concentrated, and artificially packaged 'supplements,' we may be doing ourselves harm. They may be toxic, ineffective, or contaminated (all of which are not uncommon)." Here are five supplements you should never take, according to medical experts. Read on—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.

The market for male sexual dysfunction supplements is substantial—but many doctors warn against using them, as they have not been studied scientifically and could be potentially dangerous. "Most are a phenomenal waste of money, in my opinion," says Dr. Michael O'Leary, a urologist at Harvard-affiliated Brigham and Women's Hospital.6254a4d1642c605c54bf1cab17d50f1e

St. John's Wort has been shown to interfere with prescription medications including antibiotics, antiretrovirals, and birth control. "Patients must be encouraged to discuss their use of herbal remedies with their physician, and the prevalent misconception that natural always equates with harmless must be effectively refuted," says Edzard Ernst, the world's first professor of alternative medicine. "Regulatory bodies should perhaps take a fresh look at whether herbal medicines need regulation, since the perception of `risk-free' may reflect incomplete understanding."

If something sounds fishy, it usually is—omega-3 fish oil supplements are not FDA-regulated and could contain dangerous levels of mercury and pollutants. "There are no convincing data to suggest that omega-3 supplements can prevent a first heart attack in at-risk people," says Dr. Pieter Cohen, associate professor of medicine at Harvard Medical School.

While there is evidence that vitamin C, D, and zinc can help support your immune system, there is no vitamin that can 'cure' COVID-19. "When it comes to preventing or treating COVID-19, I'd rely more on the recommendations from the CDC than on unproven supplements," says Robert H. Shmerling, MD.

Taking unregulated selenium supplements could cause heart attacks and kidney failure. "Selenium is an element necessary for normal cellular function, but it can have toxic effects at high doses," according to a paper published in JAMA Internal Medicine investigating selenium poisoning. "Toxic concentrations of selenium in a liquid dietary supplement resulted in a widespread outbreak. Had the manufacturers been held to standards used in the pharmaceutical industry, it may have been prevented."