If you use Jack3D to give your workouts a jolt or OxyELITE Pro to help you lose weight, stop. Now. And throw away whatever stash of the performance-enhancing powder or "fat-burning" capsules you have left.

These popular supplements, both made by USP Labs, contain the dangerous stimulant dimethylamylamine, known as DMAA. Already banned in the U.K., Canada, and several other countries, DMAA can jack up blood pressure, trigger heart attacks, and has been blamed for a handful of deaths in recent years. Still, here in the U.S., you could buy DMAA-containing products at your neighborhood GNC. The good news is, that's about to change.

On April 11, after an extensive yearlong safety review, the Food and Drug Administration finally deemed DMAA illegal. The agency issued a public warning telling consumers to avoid the stimulant and vowing to get supplements containing it off store shelves.

"Last spring, the FDA began raising questions about DMAA's safety and its use in dietary supplements," says Steve Mister, president and CEO of the Council for Responsible Nutrition. He says the FDA then asked all companies using DMAA in their products to present research to back up the ingredient's safety. Rather than battle the government, however, every manufacturer agreed to just ditch DMAA – except USP Labs, which stuck to its guns, saying the stimulant was safe. "From there, the FDA needed some time to make a scientific evaluation that considered all sides to determine whether this product belonged in the market," Mister says.

Time's up. The FDA spoke. DMAA doesn't belong. And on April 16, even USP Labs finally threw up the white flag, reluctantly agreeing to phase DMAA out of its products.

Still, these decisions won't immediately wipe DMAA from locker rooms and medicine cabinets. It could be some time before original-formula Jack3D or OxyELITE Pro completely disappears, so stay safe and steer clear. Also be leery of any old workout or weight-loss supplements you have lying around, since DMAA came in many more products until last year.