The active compound in yohimbe, an alkaloid called Yohimbine, functions as a monoamine oxidase (MAO) inhibitor to increase levels of the neurotransmitter, norepinephrine. Yohimbine also acts as a central nervous system stimulator, where it blocks specific receptors (alpha-2 adrenergic receptors) and may increase energy levels and promote fat oxidation. In addition to these effects, yohimbe can also dilate blood vessels – making it a potentially useful treatment for erectile dysfunction and some forms of impotence in men. Because of the MAO inhibition, yohimbe is occasionally recommended as a treatment for mild depression – but St. John’s wort has much better clinical support for effectiveness and safety.
Although yohimbe is frequently promoted as a "natural" way to increase testosterone levels for muscle building, strength enhancement and fat loss, there is no solid scientific proof that yohimbe is either anabolic or thermogenic. Results from a few small trials show that yohimbine can increase blood flow to the genitals (an effect that may occur in both men and women). As such, yohimbe may be effective in alleviating some mild forms of both "psychological" and "physical" impotence. In the few studies conducted on the purified form of yohimbine, only about 30% of subjects reported beneficial effects in terms of erectile function and sexual performance.
As the number of yohimbe products on the retail market increases, concerns about their safety are raised because of the reported toxicity of yohimbine (the major alkaloid of the plant). Reported side effects from yohimbe use include minor complaints such as headaches, anxiety and tension to more serious adverse events including high blood pressure, elevated heart rate, heart palpitations, and hallucinations. People with high blood pressure and kidney disease should avoid supplements containing yohimbe as should women who are (or who could become) pregnant (due to abortion risk). Also, caution should be used with yohimbe taken in combination with certain foods containing tyramine (red wine, liver, and cheese) as well as with nasal decongestants or diet aids with ephedrine or phenylpropanolamine (which could lead to blood pressure fluctuations). Occasionally, yohimbe is combined with serotonergic supplements (such as St. John’s wort or 5-HTP) to increase their effectiveness. It is not recommended to combine yohimbe with other anti-depressant supplements or medications except under the advice and supervision of a nutritionally-oriented physician.
For nearly a century, yohimbe has been used as an aphrodisiac and sexual enhancer - although no effect on human sex drive or performance has been adequately demonstrated. Yohimbine (the drug) has been evaluated in the management of erectile disorder in a few small studies, where it appears to have a modest therapeutic benefit over placebo (especially in "psychological" erectile dysfunction). Laboratory analyses (via chromatogram) of commercial yohimbine extracts, however, indicate that although many products contained measurable quantities of the alkaloid yohimbine, the vast majority are largely devoid of effective levels of the compound. Concentrations of yohimbine in commercial yohimbe products typically range from zero to almost 500 ppm (compared with over 7000 ppm in authentic yohimbe bark). Because yohimbe bark has been reported to contain up to 6% total alkaloids, 10-15% of which are yohimbine, it is likely that most supplements containing yohimbe also contain undeclared diluents (which you’re paying a high price for)
Because there are more effective and safe supplement remedies for increasing circulation to promote erectile function (arginine, cordyceps and ginkgo biloba), enhancing muscle strength (HMB and creatine) and weight loss (green tea, banaba leaf and gymnema) and relieving mild depression (SAM-e and St. John’s wort), yohimbe is of limited value.
Although there are no standard accepted dosage recommendations for yohimbe, it is known that more than 40mg/day of yohimbine can result in adverse side effects such as dizziness, headaches, loss of coordination and hallucinations. Typical daily amounts of yohimbine alkaloids found in commercial supplements (label claims) are often in the range of 10-30mg and occasionally standardized to yohimbine or total alkaloid content.