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Yohimbine hydrochloride (HCl) is a prescription stimulant that is most commonly known to help fight against erectile dysfunction.  Yohimbine is also available as a dietary supplement and is used to stimulate sex drive and improve sexual performance, primarily in men. 
More recently, bodybuilders have been seen using yohimbine for fat loss.   And since it is a stimulant, athletes are also taking yohimbine pre-workout to boost their energy levels and maximize their results at the gym.  
The difference between yohimbine vs yohimbe is that yohimbine is the active ingredient in the bark of an African tree called yohimbe.   Yohimbine is a naturally occurring indole alkaloid found in yohimbe bark.  In traditional African medicine, yohimbine has been relied upon for centuries for its aphrodisiac, anesthetic, and healing properties.  
Benefits and Effects
The potential health benefits of yohimbine, as published in several animal and human studies, include:
Treating Erectile Dysfunction
Short-term treatment with an oral combination of yohimbine and L-arginine improved mild to moderate symptoms of erectile dysfunction in a cohort of married adult males.  However, impotence can be a consequence of one or more symptoms, including cognitive, emotional, hormonal, physical, and psychosocial impairments. It is difficult to discern precisely which symptoms have been attenuated thanks to yohimbine treatment. 
In another human study, a third of the male subjects experienced either partial or full restoration of sustained erections after two to three weeks of oral yohimbine treatment.  The positive effect was observed by an increase in penile blood pressure.  All of the studies concluded that the usage of yohimbine for erectile dysfunction was safe and worthwhile as a first line of treatment.  
In two separate rat studies, yohimbine supplementation increased sexual arousal, sexual motivation, and frequency of ejaculation.   Furthermore, in a male human study, yohimbine was found to be an effective antidote for sexual dysfunction associated with anti-depression medication.  These observations could indicate that alpha-adrenoreceptor antagonists, like yohimbine, play a significant role in the sexual arousal of men, in particular. 
In fact, female rat and human studies did not observe any significant effect on sexual behaviour following yohimbine treatment.   Yohimbine did not increase or decrease sexual desire in female human participants.  However, it is important to note that these women suffered from hypoactive sexual disorder. It is unknown whether the same outcome would take place in women without sexual dysfunction. The difference in treatment effect of yohimbine between men and women suggests that libido may be a sex-dependent chemical reaction.
Accelerating Weight Loss
Oral yohimbine administration in healthy adult males resulted in the most significant increase in lipid mobilization when compared with other alpha-adrenoreceptor antagonists.  Likewise, the consumption of yohimbine accelerated fat breakdown in healthy adult women, especially when taken before a meal.  In both studies, yohimbine-induced lipid mobilization led to an increase in synaptic norepinephrine.   Thus, it led to an increase in lipolytic activity.  
However, the lipid-mobilizing effect of yohimbine in obese women appears to be dependent on caloric intake.  In the study where caloric intake was not a controlled variable, obese women saw no significant effect after yohimbine supplementation.  Yet, when obese female subjects were limited to a low-energy diet (1,000 kcal/day) for the duration of three weeks, yohimbine significantly increased mean weight loss effectiveness. 
Intensifying Cardiovascular Benefit
In conjunction with a hypocaloric diet, the addition of yohimbine increased cardiac load during dynamic exercise in obese women.  This means that the cardiovascular benefits of aerobic physical activity are enhanced as a consequence of yohimbine intake. Pre-exercise administration of yohimbine has also been shown to boost lipolysis during and after exercise, without any significant increases to heart rate or blood pressure. 
Elevating Energy Levels
Yohimbine is classified as a stimulant, which means that upon entering the body’s bloodstream, the pharmaceutical will increase the activity of the nervous system. In the case of yohimbine, its effects stimulate the sympathetic nervous system—also known as the fight or flight response.  
Trained endurance athletes may opt to take yohimbine pre-workout to elevate their energy levels and heighten their physiological responses to physical exertion.  The better an individual is trained, the more accustomed their body will be to high intensity exercise. By taking yohimbine, the hormonal balance of a trained athlete becomes comparable to an untrained individual, thereby allowing them to further their training. 
Reducing Fear and Social Anxiety
Preliminary animal research findings report that yohimbine treatment successfully facilitated fear extinction in conditionally feared mice.  These results suggest that alpha-adrenoreceptor antagonists may contribute to the process of fear extinction in humans, as well as in mice. However, results from human studies are not yet conclusive. Thus far, it appears that the administration of yohimbine or placebo both have positive effects on fear extinction in claustrophobic human subjects. 
A prescription for yohimbine could help treat the symptoms of people living with type 2 diabetes. The onset of type 2 diabetes has been associated with an alpha-adrenergic receptor. The idea behind yohimbine treatment for diabetes is to utilize the antagonist properties of the drug to overcome the lack of insulin. In a study, yohimbine decreased blood glucose levels and increased insulin concentrations in rats with type 2 diabetes.  
Decreasing Risk of Blood Clots
Similar to how it works against alpha-adrenoreceptors in the management of type 2 diabetes, dietary supplementation with yohimbine can also inhibit epinephrine-induced blood clotting.  Epinephrine is responsible for the regulation of blood clots. By inhibiting the alpha-adrenoreceptors, yohimbine promotes the conversion of epinephrine to norepinephrine, thus reducing the risk of blood clots. 
How Yohimbine Works
Yohimbine is a naturally occurring indole alkaloid found within the bark of the yohimbe tree.   Indole alkaloids execute metabolic functions that affect both the central and peripheral nervous systems, but yohimbine acts primarily on the peripheral system.  More specifically, yohimbine hydrochloride is an antagonistic alpha-2-adrenoreceptor. 
Alpha-2-adrenoreceptors are the receptors found on fat cells that do not mobilize lipids effectively.  This means that when hormones, like epinephrine and norepinephrine bind to these alpha-receptors, little to no lipid mobilization occurs. Consequently, little to no fat is burned.
An antagonist of the alpha-2-adrenoreceptor, like yohimbine, is intended to target alpha-receptors and inhibit them by binding to them. That way, epinephrine and norepinephrine can more readily bind to the beta-receptors to promote more efficient lipid mobilization.
The inhibitory effect of yohimbine leads to an increased rate of norepinephrine production, and therefore a higher concentration of norepinephrine within the sympathetic nervous system.  Depending on where norepinephrine is released in the body, there will be varying outcomes. In the heart, a rise in norepinephrine will cause the heart to pump more blood, increasing its cardiac output.  In general, elevated levels of norepinephrine in any tissue will stimulate blood flow to that region. This, in part, explains the mechanism by which yohimbine can prevent erectile dysfunction and enhance sexual drive.   
According to pharmacological analysis, the half life of yohimbine is rapid, between half a minute to eighteen minutes after consumption.  The effects of yohimbine are likely to last anywhere from a quarter of an hour to two and a half hours, at most. 
The general recommendation for a yohimbine HCl dosage is 0.2mg per kg of bodyweight. Following this guideline, you should be able to notice effective weight loss using yohimbine without significant cardiovascular side effects.
The maximum yohimbine dosage for erectile dysfunction is 42mg.  You should exercise caution when taking such high doses, as the more serious side effects of yohimbine HCl are more likely the higher your dosage.
An appropriate yohimbine dosage for fat loss is 20mg per day, divided into two equal portions.  It is recommended that you take your doses before a meal to offset any fluctuations in insulin levels, as a result of the yohimbine.
Even at the recommended dosages, the consumption of yohimbine comes with several potential side effects. Some of the most common, but also most minor, yohimbine hydrochloride side effects include anxiety, headache, dizziness, elevated blood pressure, and rapid heartbeat. 
At higher doses, yohimbine can even cause psychotropic effects, like hallucinations. Individuals who suffer from any kind of heart condition and/or high or low blood pressure should not take yohimbine. The potential for drastic changes in heart rate and/or blood pressure could put your health in severe danger.  Likewise, yohimbine should never be combined with an anti-depression medication unless you have been told otherwise by a healthcare professional.
As with any dietary supplement, it is best to err on the side of caution to reduce any yohimbine-related side effects—especially at the beginning of treatment. It is also recommended that you refrain from taking yohimbine regularly on a long-term basis, as there is insufficient evidence to support it.
A popular choice for men looking to enhance their sexual performance with pharmaceuticals is a stack combination of L-arginine glutamate and yohimbine hydrochloride.   The combined oral administration of these stacked supplements has been shown to be a safe and effective short-term solution to erectile dysfunction. 
While it may seem like a good idea to take yohimbine with caffeine, the safety profile of the stack has not yet been determined. The side effects of yohimbine and caffeine together may lead to overstimulation of the central and peripheral nervous systems.  Overstimulation will likely negate the individual benefits of yohimbine and caffeine on their own.