I always mix my own, especially now that the premixed stuff on the market sucks. I never liked the herb, ephedra because the dosing is unreliable. That's why it was pulled off the shelf. Ephedrine, the drug, is dosed exactly. The stack is 20 mg ephedrine, 200 mg caffiene, and an aspirin which I think is 325 mg. The aspirin shuts down the negative feedback loop and increases the effectiveness. But, this stack is pretty strong and can cause health problems.
My own editorial comments: I quit using this stuff years ago because I felt I was becoming adicted (probably too strong of a word), I didn't like the thought of heart damage, and I noticed some sexual side effects. Use at your own peril. Even at my peak usage I would only do one dose in the morning. I can't imagine using it 2-3 times a day like some do.