Stacker 2 is a fat burner, so it's some combination of ephedrine, caffeine, and maybe aspirin. There have been plenty of studies on the EC combination, and it's been shown to be somewhat effective for boosting metabolism slightly. It's not a magic weight loss pill, so if you're unwilling to put a diet and exercise plan together, it won't do a thing for you other than make your heart race.
Stay within the recommended dosage, or better yet figure out how many mg of ephedra and caffeine are recommended in the studies, and buy your own ephedrine and caffeine tablets -- it's cheaper that way. If you have a pre-existing heart condition or high blood pressure, you should talk to a doctor. It can make you more irritable, I noticed that initially. I took half doses to start, to see how my body would react.
I tried EC for a few months and personally don't think it did much for weight loss. It supposedly can suppress appetite, but I never felt that it did for me. The initial energy rush was the best part of it, but that fades away as you grow tolerant to it. If I used it again, I'd just use it before workouts as an energy booster.