If you choose to take an over-the-counter supplement for weight loss, muscle building, or even sexual enhancement you probably trust what it says on the bottle. The labels are often filled with vitamins, minerals, and other substances meant to make you look or feel better, but you might also be getting something you never intended.

A new study published in JAMA Network Open offers an all-encompassing look at instances of prescription drugs being found in many different supplements, and it happens with startling regularity. A shocking 20% of supplements tested by the Food and Drug Administration was found to contain prescription medications that had no business being included.

The study focused on various warnings and alerts put forth by the FDA from 2007 through 2016 regarding tainted supplements. A total of 776 supplements were found to be tainted with pharmaceutical ingredients often associated with the claims made by the supplement manufacturer.

For example, some muscle-building supplements were found to include actual steroids or similar ingredients, while sexual enhancement supplements were found to contain sildenafil, the active ingredient in Viagra. Over 150 of the tested supplements contained more than one unapproved ingredient.

The study goes on to explain that some of the supplements which received warnings from the FDA were found to still contain unapproved prescription drugs long after the discovery was made. The drug inclusions were often different than the ones previously discovered, suggesting that the manufacturers were knowingly altering their formulation with new additions that still broke the rules.

Aside from the regulatory issues associated with selling a drug in a supplement’s clothing, there’s a very real risk of harm to consumers who choose to put these pills in their bodies. Some of the drugs found, like steroids, stimulants, and anti-depressants can have serious adverse effects, causing symptoms issues that medical professionals wouldn’t suspect a supplement as causing. Additionally, patients who take prescription medications already and then add a supplement without their doctor’s knowledge could be at risk of drug interactions without even knowing it.