The EC Stack, In Depth
EC, or ephedrine + caffeine, is one of the best over the counter fat loss options that we have. It is effective to the point it was initially thought to be dangerous. More time and study has only shown the opposite. Athletes: please know that ephedrine is banned by the NCAA, MLB, NFL, PGA, and WNBF.
It was brought to market as a bronchodilator, and in the United States is now only to legal to sell as such (or as prescribed). It is readily available on supplement store shelves elsewhere, such as in Canada.
ECA is quite stimulatory, and by itself Ephedrine is a fairly potent B2 agonist. To potentiate its effects we combine it with a methylxanthine, the most readily available and effective of which is caffeine. The combination of the two is what works the real magic 
This is most often taken as: 200mg caffeine +25mg ephedrine
Some people like to still incorporate a baby aspirin with their first dose (The ECA stack) but this is totally unnecessary to get the results. It could be of benefit for those with concerns for side effects by preventing platelet aggravation (and its overall cardiac risk preventative effects) as EC use does liberate a lot of FFAs (fatty free acids) into the bloodstream as well. That said, EC aloneshould be safe in healthy individuals, this is what most have progressed to using.
For those who have not tried it, know that this kicks a lot harder (stimulant effect) than caffeine alone. Using EC or ECA can and does initially raise blood pressure and heart rate, among other things all reported at this reference 
We have studies in a variety of test populations now, and with HR and BP being primary concerns one would think it may be unsafe for the obese. But we did that study  in obese women for 8 weeks.
Results: the E + C group lost 4.5 kg more body fat and 2.8 kg less fat-free mass (FFM).
It was also safe at 24 weeks in a much larger obese group Also losing statistically greater amounts of FFM.
Results: Mean weight loss was found to be 16.6 kg after 6 months when E+C was provided as an adjuvant to an efficient hypoenergetic diet, which was 3.4 kg higher than in the placebo group.
That is HUGE for popping some pills, and it had no real drawbacks for most. From that same study: ”...after 8 weeks blood pressures were indistinguishable from those of the placebo group. E+C has no adverse effect on glucose and lipid metabolism, but has been shown to prevent the decline in HDL-cholesterol caused by weight loss’
Long term EC use can actually lower your blood pressure, secondary to weight loss.
Let’s take a closer look here:
Diagram is from the full text of 
Pretty clear cut that you lose weight faster with EC, this is also demonstrating the reason we always want caffeine to be used in tandem. Combine that with what we know from above that this (as a b-agonist should) can lead to increases of lean mass (or the more likely result of more lean mass preserved, as one would generally be in a calorie deficit set to lose weight overall), EC seems to be a dream come true for anyone looking to lower body fat.
It also has lab indications of positive effects in both WAT/BAT, but these studies were in rats and it’s something we simply know to now always transfer to the human model.  I wouldn’t put too much weight on this, but we know we are getting the desired end result regardless.
It is worth noting that effects of the EC stack will be just up stream of cAMP, as well. It is thought, and actually shown in vivo now to be synergistic to also elevate cAMP by other means while EC is hitting your b-2 receptors.  One way to do this as shown there is via Forskolin, which is your best bet at raising cAMP and the most studied ingredient for it.