The sports supplement “Craze,” popular in the United States and other countries, contains a meth-like chemical, USA Today reports.

Scientists in the United States and South Korea who tested the chemical say it appears to have originated as an illicit designer recreational drug. Craze is sold as a pre-workout powder made by the company Driven Sports. The powder is marketed as containing only natural ingredients, the article notes. The scientists began testing Craze after athletes who said they had used the supplement failed several urine drug tests.

The findings appear in the journal Drug Testing and Analysis.

The U.S. researchers said the same chemical is also found in another supplement, Detonate, marketed as a weight-loss pill by Gaspari Nutrition.

“These are basically brand new drugs that are being designed in clandestine laboratories where there’s absolutely no guarantee of quality control,” study co-author Pieter Cohen of Harvard Medical School told the newspaper. “It has never been studied in the human body. Yes, it might make you feel better or have you more pumped up in your workout, but the risks you might be putting your body under of heart attack and stroke are completely unknown.”

Walmart.com and several other online retailers stopped selling Craze earlier this year after USA Today reported that tests detected amphetamine-like compounds in the product. It continues to be sold in GNC stores and on other websites.

After that article appeared, the company said in a statement, “Craze is a legal supplement that provides people with a tool to enhance their workouts, by combining natural extracts to increase their energy. Craze conforms to all U.S. federal regulatory requirements and is proven safe when used as directed. As is the case with any such supplement, the product and its ingredients are subject to regulation by the U.S. Food & Drug Administration.”