A Productive Fat Burning Combo
There’s a lot of hype in the bodybuilding and fitness community about an ephedrine, caffeine, and aspirin stack (also known as the ECA stack).
However, for those of us who are unable to obtain ephedrine or are weary of its effects, a combination of caffeine and yohimbine is a much safer substitution.
Caffeine and Fat Loss
Caffeine on its own is known to be a good fat-loss product because it creates a metabolic spike roughly 30 minutes after being taken, which equates to burning almost 8 calories an hour.  Although 8 calories an hour does not seem like much, the real reason caffeine acts as a great weight-loss product is because it is shown to suppress appetite. 
Yohimbine for Fat Loss
Yohimbine is also shown to be a promising weight-loss product on its own. It is shown to increase thermogenesis which essentially warms up the body enough to start burning fat.  It is also known to prevent “fat loss from stopping”  which creates a perfict synergism with caffeine.
A lot of people do note that yohimbine is ineffective when taken with food in the stomach, and notes the stimulatory properties only exist when taken before meals. This may or may not mean that it is ineffective as a fat loss product when taken on a full stomach; however, it would be safe to assume the fat loss properties are much more prominent when taken on an empty stomach.
My suggestion (and what I have seen work best for me) is to take the stack 20-30 mins prior to a meal. This will allow the products to generate their fat-loos potential, but will eliminate the shake after-effects due to the stimulation by adding nutrients to your body.
The Caffeine + Yohimbine Stack
Because both caffeine and yohimbine are stimulatory, it’s generally a good idea to start off with a low dose and work up from there. A typical dose is 200mg of caffeine and 2.5mg(one primaforce pill) of yohimbine up to three times a day. Also, because tolerance exists, it’s also generally a good idea to cycle the yohimbine and caffeine stack for maximizing efficacy.
Unfortunately, ephedrine is a much more powerful fat loss product than yohimbine, however it is banned in the US due to it being a precursor to methamphetamine. It’s also much more likely to be abused recreationally and has addictive properties. Yohimbine has proven to be a sufficient substitute for the ephedrine ingredient time and time again.