Here's a good write up from an old buddy of mine from my MindandMuscle.net days
It is from 1fast400 by David Tolson
1. What is yohimbine?
Yohimbine is an alkaloid found in the inner bark of a tree that grows in southern Africa, Corynanthe yohimbe. Yohimbe has been used for centuries as an aphrodisiac, and alkaloids derived from this tree have been studied in depth. Yohimbine is now used primarily in veterinary medicine and in the treatment of erectile dysfunction, and it may also be useful in the treatment of obesity.
2. What application does yohimbine have?
Yohimbine has not been researched as thoroughly in the area of fat loss as many other weight loss aids, especially where clinical trials are concerned, but the existing data is promising. A 3-week study in 1991 on 20 obese females on 1000 calorie diets found that 20 mg of yohimbine daily increased weight loss 3 lbs. over placebo (1). Multiple studies have found that yohimbine increases the amount of non-esterfied fatty acids (NEFAs), a product of lipolysis (the breaking down of fat), in the bloodstream in both lean and obese individuals (2, 3), and that this effect persists for at least 14 days, indicating that rapid tolerance does not develop (4). Yohimbine is also an appetite suppressant, and decreases energy intake in both lean and obese mice (5).
3. How does yohimbine work?
Yohimbine works by blocking alpha(2) adrenoreceptors. There are a number of feedback mechanisms that prevent the release of norepinephrine (NE), one of the body's primary lipolytic hormones. When NE is released, such as in periods of stress or after taking a sympathomimetic (such as ephedrine), it stimulates both the alpha and beta adrenoreceptors. Stimulation of the beta adrenoreceptors causes the breakdown of fat while stimulating the alpha(2) adrenoreceptors has the opposite effect, preventing the release of NE and lipolysis. Yohimbine prevents this negative feedback mechanism, thus increasing NE release and lipolysis.
There are a number of reasons why alpha(2) inhibition is specifically useful. First, while the beta-adrenergic system primarily controls lipolysis during periods of intense activity, during rest, which makes up most of our day, the alpha-adrenergic system is in control (6, 7). Also, "stubborn fat" areas – usually the abdominal area in men and the glutofemoral area in women – contain a higher ratio of alpha(2) receptors (7), making yohimbine particularly effective in these areas (whereas other drugs that increase NE may be somewhat counterproductive). Finally, alpha(2) blockade increases blood flow in adipose tissue (7), which prevents fat from being retained in the area (8).
3. What other benefits does yohimbine have?
Aside from being a fat loss agent, yohimbine is well known as a sexual stimulant. Studies indicate that it increases copulatory behavior and reduces sexual exhaustion in male rats (9, 10). A recent review of the literature found that yohimbine, especially in combination with drugs that facilitate the action of nitric oxide, is effective in the treatment of male erectile dysfunction (11), and a study in women found yohimbine combined with L-arginine glutamate to increase sexual arousal in women with sexual arousal disorder (12). Yohimbine also slightly raises serum testosterone levels in men (13).
4. What are the side effects of yohimbine?
Anxiety is the most common side effect seen with yohimbine, especially higher doses, and for this reason it should not be used by individuals prone to panic attacks or with stress-related disorders (14, 15). Other common side effects are increased heart rate and blood pressure, although these do not appear to be a problem at the doses used for weight loss (2, 3). Other side effects associated with elevated levels of NE, such as insomnia, can also be expected. All of these side effects disappear after termination of use (11).
5. What form of yohimbine is best?
Yohimbine is available as an herbal yohimbe extract or pure yohimbine HCl, and it is also found in some topical fat loss solutions. Yohimbe extracts contain a variety of alkaloids, and yohimbine only makes up 10-15% of the alkaloids present (16). The activity of many of these alkaloids is not well known, and some of them may have toxic effects (there are many reports that yohimbe is an MAOI), which makes pure yohimbine HCl both a safer and more consistent alternative. For those wishing to deliver a higher quantity to a specific "trouble area" without the side effects of systemic delivery, topical solutions (such as Lipoderm-Y) are effective (17).
6. How should yohimbine be taken?
The dosage of .2 mg/kg (approximately 1 mg per 10 lbs.) per day is relatively free of side effects and effective for weight loss (2, 3), while .1 mg/kg is more commonly used for sexual stimulant effects. For fat loss, yohimbine is generally taken twice daily, in the morning and afternoon. It is best taken on an empty stomach, as taking it with a meal can reduce its lipolytic effects (3). The half-life of yohimbine is short (1-2 hours), but the half-life of a metabolite with similar activity, 11-hydroxy-yohimbine, is 6-8 hours (18), so it is not necessary to take it every 2 hours. It is best to start with half the dose or less to see how sensitive you are to yohimbine, as inter-individual bioavailability and tolerance can vary greatly.
7. What are some good supplements to take with yohimbine?
As covered above, arginine and other NO enhancers may operate synergistically with yohimbine as a sexual stimulant. It is also probably synergistic with caffeine for fat loss through PDE inhibition.
A possible synergism between yohimbine and ephedrine hasn't been thoroughly explored, and the information that exists is somewhat contradictory. In theory, they should work well together as yohimbine blocks one of the negative feedback mechanisms that would normally make ephedrine less effective. Cell culture studies confirm that yohimbine increases the lipolytic effects of beta(3) agonists (19). However, a study using rats indicated that yohimbine blocked the effects of the same beta(3) agonist, indicating that the two may antagonize each other (19). Additionally, a study on cardiovascular variables found that ephedrine and caffeine together were safe, but the addition of yohimbine may produce undesirable effects (20). So it is still unknown whether the combination of yohimbine and ephedrine produces any additional benefit, and whether it is justified by the potential dangers
