Yohimbin

Yohimbine blocks the three alpha-2 receptors. At nerve endings they slow further release of noradrenaline, at fat cells the release of fat. If the brake falls away, noradrenaline rises and, via beta receptors, fat release too.

In the 1988 study yohimbine raised fatty acids and glycerol only in fasted men, more so during exercise. After a meal the effect was gone completely. A beta blocker partly cancelled it.

20 professional footballers took yohimbine in two doses a day or placebo for three weeks. Body fat fell from 9.3 to 7.1 percent in the yohimbine group, with placebo it was 9.2 at the end. Body weight, muscle mass and all performance tests stayed the same, no one reported side effects. The group was small and young.

A 1998 meta-analysis found seven randomised trials, yohimbine was clearly superior to placebo (odds ratio 3.85). Serious side effects were infrequent and reversible. Since PDE-5 inhibitors exist, yohimbine hardly plays a role there.

In 13 men the half-life was between a quarter of an hour and two and a half hours, the data also suggested a slow phase of about 13 hours. Almost everything is broken down by the liver, only 0.5 to 1 percent appears unchanged in urine. Absorption varies a lot from person to person.

Yohimbine boosts the sympathetic nervous system. At higher doses agitation, anxiety, high blood pressure and a racing heart are typical. A clear benefit for muscle building or performance is not proven. In the short 1988 study, by contrast, pulse and blood pressure stayed largely stable.

ChEMBL lists yohimbine with phase 3 as the highest phase. The registry lists 51 trials, the phase 3 trials test yohimbine as an add-on to behavioural therapy in anxiety and phobia. Drugs@FDA has no product.