"A possible synergism between yohimbine and ephedrine hasn't been thoroughly explored, and the information that exists is somewhat contradictory. In theory, they should work well together as yohimbine blocks one of the negative feedback mechanisms that would normally make ephedrine less effective. Cell culture studies confirm that yohimbine increases the lipolytic effects of beta(3) agonists (19). However, a study using rats indicated that yohimbine blocked the effects of the same beta(3) agonist, indicating that the two may antagonize each other (19). Additionally, a study on cardiovascular variables found that ephedrine and caffeine together were safe, but the addition of yohimbine may produce undesirable effects (20). So it is still unknown whether the combination of yohimbine and ephedrine produces any additional benefit, and whether it is justified by the potential dangers."
Ehhh??
Safe?