Sometimes it can seem like weight loss, significant or otherwise, requires nothing short of a miracle. But be wary of those miracle pills — not all of them follow through on their promises. The US. Food and Drug Administration recently issued a public warning that many weight-loss products marketed as dietary supplements actually contain hidden active ingredients found in prescription drugs, untested compounds and unsafe drugs that have been removed from the market.

The FDA has found supplements containing fluoxetine, the active ingredient in Prozac, a prescription drug used to treat depression and other conditions. Other ingredients found include lorcaserin (lor-cah-sehr-in), sibutramine (si-byu-tra-mean) and triamterene (tri-am-tehr-een), a powerful diuretic with serious side effects.

Even natural-looking products such as bee pollen or Garcinia cambogia (Gar-sin-ia cam-boj-ia) may contain hidden components which may be harmful for people who have irregular heartbeats, high blood pressure or bipolar disorders.

According to the Federal Food, Drugs and Cosmetic Act, dietary supplement firms do not need FDA approval before marketing their products. But the FDA does investigate when they suspect safety issues. In 2014, they released over 30 public notifications and recalled seven tainted weight loss products.

The safest way to seek weight loss with the aid of medication is to talk to your doctor beforehand.

Be sure to watch out for products claiming quick fixes … like losing 10 pounds in a week, words like “scientific breakthrough” or “guaranteed” and marketing campaigns through mass emails. And take personal testimonials with a grain of salt. Many of them are exaggerated.

If you suspect something may be tainted, the FDA asks that you report that information online. If it sounds too good to be true, it probably is.