The US Food and Drug Administration on Friday questioned the safety of DMAA, a stimulant used in dietary supplements, alleging that marketers were illegally selling the chemical.
Popular with fitness buffs seeking an edge or weight loss, the brands include Napalm, Code Red, Hemo Rage Black, Nitric Blast and Jack3D.
The FDA said it issued warning letters to 10 manufacturers and distributors of dietary supplements containing the ingredient for failing to submit evidence of the safety of their products.
"Before marketing products containing DMAA, manufacturers and distributors have a responsibility under the law to provide evidence of the safety of their products. They haven't done that and that makes the products adulterated," said Daniel Fabricant, director of the FDA's Dietary Supplement Program.
In the warning letters, the FDA also said it was not aware of evidence or history of use to indicate that DMAA is safe.
Dimethylamylamine, also referred to as "geranium extract," is often touted as a "natural" stimulant, the FDA said.
"The agency additionally warned the companies that synthetically produced DMAA is not a 'dietary ingredient' and, therefore, is not eligible to be used as an active ingredient in a dietary supplement," the agency said.
The FDA letters raised concerns that DMAA is known to narrow blood vessels and arteries, which can lead to shortness of breath and heart attack.
The federal agency said it had received 42 adverse reports on products containing DMAA, including psychiatric disorders and death.
In December, the Army Times reported the Defense Department had ordered an end to on-base sales of a number of workout supplements containing DMAA, pending a review of its safety.
The Pentagon worried that the substance may have contributed to the deaths of two soldiers who had heart attacks during physical training after using DMAA products, as well as the cases of three soldiers and two Marines who collapsed during heavy exercise, the specialty newspaper reported.
The FDA said the firms have 15 business days to respond with the specific steps they will take to address the issues in the warning letters.
The 10 companies warned are: Exclusive Supplements, Fahrenheit Nutrition, Gaspari Nutrition, iSatori Global Technologies, Muscle Warfare, MuscleMeds Performance Technologies, Nutrex Research, SEI Pharmaceuticals, SNI, and USP Labs.