There was a big DMAA craze back in the days. Supposed to be, like many stim to be a new "ephedra".
It does work big time, slightly different than ephedrine tho, you are more mentaly focused with DMAA a very pronounced tunnel vision effect, especialy the first times you take it.
Like ephedrine it cuts appetite and works synergisticly with caffeine. It used to be in most pre workouts and fat burners.
But unlike ephedrine which is relatively safe people quickly complained about a lot of unwanted sides : major crash, limp dick, mood disturbance, withdrawal, tolerance that sets in very fast... Just to name a few.
People also started abusing it and some dying or getting messed up. The most famous case is some soldiers who took Jack3d (a DMAA based pre workout) and died during an intense exercise session.
The FDA starting investigating and unsurprisingly found out DMAA is nowhere to be found un Geranium like it was marketed and is simply a synthetic amphetamine and the stuff got banned.
Really the only thing good about it was the fact it was legal. Just get ephedrine instead.