These are the supplements that are the most likely to send you to the emergency room

Because of the way the US Food and Drug administration defines them, however, supplements are not regulated as drugs. It is only when a specific supplement is shown to cause significant harm that it is called out as unsafe.

With that in mind, S. Bryn Austin, a professor of behavioral sciences at the Harvard T.H. Chan School of Public Health, told Business Insider that there are three main categories of dangerous supplements to watch out for: those related to weight loss, muscle building, and sexual performance.

These, she said, are "the most lawless of all the categories and where the most problems turn up."

Last year, researchers analyzed a trove of data from 2004 to 2013 to find out which supplements were sending people to the ER the most. Their findings jibe strongly with Austin's conclusion, as you can see in the chart below.

The problem with many of these pills and powders is that they have been adulterated — often with banned pharmaceutical drugs.

"Some of these companies won't identify ingredients that they purposefully put in the products," Austin said. "Some weight-loss drugs, for example, that have been pulled from the market — we can still find these in the bottle even though they don't put it on the label."

A study of product recalls published in 2013 in the Journal of the American Medical Association found that of the 274 supplements recalled by the FDA between 2009 and 2012, all contained banned drugs. And a 2014 report found that more than two-thirds of the supplements purchased six months after being recalled still contained banned drugs.

Steve Mister, the president and CEO of the Council for Responsible Nutrition, a Washington, DC-based trade organization representing more than 150 supplement and other companies, told Business Insider that this adulteration harms other supplement companies that make legitimate products.

"There is nothing legal about supplements that contain things that aren’t on the label," said Mister.

Over the same period as the study above, 34 people died as a result of using supplements, according to a 2017 study published in the Journal of Medical Toxicology. Six of the deaths resulted from ephedra, the once popular weight-loss supplement banned by the FDA in 2004, and three people died from homeopathic remedies. One person died after using yohimbe, an herbal supplement used for weight loss and erectile dysfunction. (Certain formulations of it can be prescribed to treat erectile dysfunction.)

"Consumers should expect nothing from [supplements] because we don't have any clear evidence that they're beneficial," said Austin. "And they should be leery that they could be putting themselves at risk."