This is probably the herb with the second most well-known reputation for aphrodisiac effects, the first being ginseng. One of the more important distinctions between the two is that yohimbe would appear to work.
Yohimbe comes from the bark of the yohimbehe tree, Pausinystalia yohimbe, from West Africa: Cameroon, the Congo, Gabon, and Nigeria. It has a substance, yohimbine (predictably, I suppose), that dilates small arteries by blocking the release of neurotransmitters that would otherwise cause the arteries to constrict. This effect is referred to as alpha-2-adrenergenic receptor blocking. So what does that all mean? Well, it increases blood flow to the penis/clitoris and reduces the flow from it. Very erect, very sensitive. Therefore, a very popular substance. Studies show its effectiveness, making it as objectively true as possible.
It also seems to counter the near-infamous sexual side effects of antidepressant drugs (particularly selective-serotonin reuptake inhibitors , or SSRIs), apparently by the same means.
Some people also report mild hallucinogenic effects.
There’s a catch, of course. Prolonged use can bring on side effects such as palpitations, tension, irritability, and sweating. In other words, it essentially is the opposite of the antidepressants mentioned above. It’s very dangerous for people who have problems with their heart, liver, blood pressure, or who are taking MAO inhibitors. If you don’t have any of these problems, odds are you should be alright with yohimbe use, so long as it isn’t daily or too frequent.
The only other caution I would observe regarding yohimbe is an ethical quandary: The value of the bark has caused very poor areas to overharvest, causing endangerment or death of the very trees that help them. Even regrowing the bark takes, I am told, 10 years. There must be a way to farm this highly effective substance reasonably, but I am unaware of anyone doing so.