Some athletes say that yohimbe helps boost metabolism.

As a stimulant, yohimbe may theoretically increase fat metabolism. The main alkaloid in yohimbe is yohimbine, which can be toxic if used in excess amounts. This alkaloid blocks a particular receptor that increases sympathetic nervous system output so you get more adrenaline and, thus, increased metabolism.

Warning: This stimulant puts stress on the heart, which is especially dangerous for anyone with a heart condition. Yohimbe should only be used under the supervision of a doctor.

The ability of yohimbine, a chemical found in yohimbe bark, to stimulate the nervous system,^{1 , 2} promote the release of fat from fat cells,^{3 , 4} and affect the cardiovascular system has led to claims that yohimbe might help athletic performance or improve body composition.⁵ However, a double-blind study of men who were not dieting reported no effect of up to 43 mg per day of yohimbine on weight or body composition after six months.⁶ No research has tested yohimbe herb for effects on body composition, and no human research has investigated the ability of yohimbine or yohimbe to affect athletic performance. Other studies have determined that a safe daily amount of yohimbine is 15 to 30 mg.⁷ However, people with kidney disorders should not take yohimbe, and side effects of nausea, dizziness, or nervousness may occur that necessitate reducing or stopping yohimbe supplementation.

Patients with kidney disease, peptic ulcer or pregnant or breast-feeding women should not use yohimbe.⁸ Standard amounts may occasionally cause dizziness, nausea, insomnia, anxiety, increased blood pressure, and rapid heart beat,⁹ though all of these are rare.¹⁰ Using more than 40 mg of yohimbine per day can cause dangerous side effects, including loss of muscle function, chills, and vertigo. Some people will also experience hallucinations when taking higher amounts of yohimbine.¹¹ Taking 200 mg yohimbine in one case led to only a brief episode of hypertension, palpitations, and anxiety.¹² People with post-traumatic stress disorder¹³ and panic disorder¹⁴ should avoid yohimbe as it may worsen their condition.

Foods with high amounts of tyramine (such as cheese, red wine, and liver) should not be eaten while a person is taking yohimbe, as they may theoretically cause severe high blood pressure and other problems. Similarly, yohimbe should only be combined with other antidepressant drugs under the supervision of a physician, though at least one study suggests it may benefit those who are not responding to serotonin reuptake inhibitors such as fluoxetine (Prozac).¹⁵