If you're a workout-supplements user, you need to know that the popular supplement Craze contains a chemical similar to methamphetamine, according to a new study published in the journal Drug Testing and Analysis.

Researchers suspected that unlabeled ingredients in Craze could be the reason why some unwitting athletes had a meth-like substance in their blood.

A team of researchers from public health organization NSF International, Harvard Medical School, and the National Institute for Public Health and the Environment collected Craze samples from three outlets: a United States online supplement supplier, a GNC store, and a European supplement retailer. All three samples of Craze tested positive for dangerous levels of a methamphetamine analog, which was not listed as an ingredient.

The scary thing is that Craze isn't the only workout supplement consumers need to worry about. While the FDA regulates supplements to an extent, companies aren't required to disclose on the label whether the ingredients actually work or if there are any side effects, according to study author Pieter Cohen, M.D., general internist at Cambridge Health Alliance. “There’s no system that allows the FDA to track harmful supplements,” says Cohen. “Unless individual researchers bring this to their attention like our study, the FDA doesn’t normally take action except for cases when supplements pose immediate health risks.”

This doesn't mean that all supplements are dangerous. You just have to take extra precautions when shopping around. Cohen warns that most supplements that energize you before workouts, or those that claim to be hormonally based don't really work, and they may contain illegal, mislabeled substances. Single-ingredient supplements like creatine are usually safer options: Typically, the fewer ingredients on a label, the smaller the chance that something dangerous is lurking inside, says Cohen.

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