It's still unclear exactly how the stuff works, when it does work. Some investigators think it acts directly on the central nervous system, and others, through complex hormonal pathways. One mystery: It's known that yohimbine clears out of the blood 35 minutes after it's taken, yet most studies have shown that men usually don't notice any improvement until they've taken the drug for two to three weeks. Some researchers feel this suggests it's not yohimbine itself that's doing the trick-it's some metabolite, or breakdown product, that forms in the blood while yohimbine is being digested.

Just to clarifY here: Yohimbe is the name of a mild-mannered over-the¬counter product made from the bark of the yohimbe tree. It's sold in health food stores and elsewhere, often in pill or capsule form, in potencies ranging from 500 to 750 milligrams. But pharmaceutical yohimbine (yohimbine hydrochloride, or yohimbine Hel) is the active ingredient in the bark-extracted and refined to a purity greater than 99 percent. The research studies described here all used pharmaceutical yohimbine, generally available in 5.4-milligram tablets and sold under the brand names Yocon, Yohimex, Aphrodyne or others. The drug ranges in price up to $40 for 100 tablets.

According to a survey conducted by Men's Health Newswtter, the potencies¬and the prices-of various mail-Dfder yohimbe concoctions are likely to vary wildly. Even the potency of pills in the same bottle may vary. So if you're seriously interested in giving yohimbine a try, it's best to have a doctor prescribe it for you. A physician can adjust the dosage, monitor your progress and - if it doesn't work-recommend the next treatment to try.
There is one precautionary note, however: Some researchers have found that yohimbine can boost blood pressure, at least a little, in some men. In one study at Wayne State University in Detroit, for instance, researchers found that yohimbine tended to increase systolic blood pressure (that's the higher number in the blood pressure reading), although not significantly, in the men under study. It did significantly increase the men's heart rate, though, as well as boost blood flow in their forearms -leading the researchers to suggest that it might be useful as a treatment for low blood pressure in some patients. On the other hand, in another study in which 33 men were treated with the drug, researchers reported that there was no effect on blood pressure, nor were there any other side effects associated with yohimbine.

The bottom line in all this? If you're going to try yohimbine, and you're prone to high blood pressure, you need to keep an eye on your pressure - and quit taking the drug if it goes up.