The ECA stack combines Ephedrine, Caffeine and Aspirin to create a, I guess you could call it a Thermogenic Cocktail. Ephedrine is a beta-adrenergic agonist. It's been regarded as a potent thermogenic but it's more effective when combined with caffeine. Caffeine increases blood adrenaline levels, therefore increasing the breakdown of fat. Throwing an aspirin in the mix seems to pick up the potency even more. I myself, find the aspirin irritates my stomach, so I omit it. If aspirin irritates your stomach, you can substitute the herbal form, white willow bark, or you can leave it out altogether. The ephedrine and caffeine stack is a potent stack on it's own. The ECA stack not only acts as a great fat burner but it's also a great appetite suppressor or just a good kick in the ass before a workout! The typical ECA stack looks like this: 25mg ephedrine, 200mg Caffeine and 300mg aspirin. You typically should take it 2-3 times a day. I myself, wouldn't suggest taking it for more than three weeks at a time, as your body gets "use" to this stack quite fast. When I use it, I usually do one day on and one day off and I use Yohimbine on the days in between my ECA stack. Some people take the Yohimbine with the ECA stack but I myself, find it far too strong.
The ECA stack is definitely not for everyone though. People with high blood pressure, heart disease, thyroid disease, diabetes etc. should refrain from using the ECA stack.
Hmmm...did I forget anything? If I did, feel free to add in.