The FDA has issued a warning for dietary supplements.
Most dietary supplements contain the stimulant known as DMAA. It's promoted as a natural way to enhance athletic performance and speed up weight loss.
The FDA says it's received reports of 86 illnesses and deaths associated with products containing DMAA.
The agency says the stimulant can increase blood pressure, result in shortness of breath and chest tightening. It's even been linked to cardiovascular problems, including heart attacks.