Yohimbine, derived from the bark of the West African yohimbe tree (Pausinystalia yohimbe), has garnered attention for its potential in treating erectile dysfunction and promoting weight loss. This article delves into the scientific evidence surrounding yohimbine's efficacy for weight loss, explores its mechanisms of action, discusses appropriate dosages, and highlights potential risks and side effects.
What is Yohimbine?
Yohimbine is an indole alkaloid found in the bark of the Pausinystalia yohimbe tree, a tall evergreen native to West Africa. The bark has been traditionally used as an aphrodisiac and in traditional medicine to treat conditions like angina and hypertension. Authentic yohimbe bark may contain up to 6% total alkaloids, with yohimbine comprising 10% to 15% of this total. The alkaloid yohimbine is also sourced from Aspidosperma quebracho-blanco and Rauwolfia serpentina. It is available in two forms: yohimbine hydrochloride, used in clinical studies, and the free base, typically found in yohimbe extract or bark.
How Does Yohimbine Work?
Yohimbine's primary mechanism of action involves blocking alpha-2 adrenergic receptors. These receptors play a crucial role in regulating various physiological processes, including the release of norepinephrine, a neurotransmitter involved in lipolysis (fat breakdown). By blocking these receptors, yohimbine inhibits the negative feedback mechanism that normally suppresses norepinephrine release, leading to increased norepinephrine levels. This, in turn, can potentially promote fat breakdown and increase metabolic rate.
Yohimbine exhibits a wide range of pharmacological activities, primarily mediated through interactions with various receptor systems. It acts as a selective α2-adrenergic receptor antagonist, exhibiting higher affinity for presynaptic α2-adrenergic receptors compared to postsynaptic ones. This leads to increased norepinephrine levels in the synaptic cleft, enhancing sympathetic activity.
Beyond α2-adrenergic antagonism, yohimbine interacts with serotonin receptors (5-HT1A, 5-HT1B, and 5-HT1D), α1-adrenergic receptors, dopamine D2 and D3 receptors, and imidazoline I2 receptors. These interactions contribute to its effects on mood, anxiety, blood pressure, and motor function.
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Yohimbine can elevate blood levels of epinephrine and norepinephrine, increasing heart rate, systolic blood pressure, and alertness. It may also enhance localized blood flow.
Yohimbine and Weight Loss: Examining the Evidence
The ability of yohimbine to stimulate the nervous system and promote the breakdown of fat tissue has led to claims that it might aid weight loss by raising metabolic rate, reducing appetite, and increasing fat burning.
Clinical Data
A systematic review of three high-quality clinical trials found conflicting results regarding yohimbine's effectiveness in reducing body weight and could not conclude that yohimbine use is effective. Studies evaluating the effect on body and muscle mass have also been inconclusive.
Study on Athletes: A study involving athletes found that 20 mg of yohimbine daily for 21 days did not affect body mass or muscle mass but did decrease body fat. No effect on exercise performance was observed. Specifically, percentage of body fat significantly decreased in the yohimbine group after the supplementation protocol (9.3 +/- 1.1 vs. 7.1 +/- 2.2%; p < 0.05). Furthermore, fat mass was significantly lower in the yohimbine versus placebo trial at postsupplementation assessment (7.1 +/- 2.2 vs. 9.2 +/- 1.9%; p < 0.05).
Study on Women: A placebo-controlled trial that included 20 women on a low-calorie weight-loss diet found those taking 5 mg of yohimbine four times per day had increased energy expenditure and greater weight loss after three weeks.
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Study on Men: A similar trial that included 47 men, taking 43 mg per day of yohimbine for six months resulted in no effect on weight loss. 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.
These mixed results suggest that yohimbine's effectiveness for weight loss may vary depending on factors such as gender, diet, exercise, and dosage.
Dosage Guidelines for Weight Loss
Total daily dosages of 0.2 mg/kg body weight have been successfully used to increase fat burning without significant implications on cardiovascular parameters like heart rate and blood pressure. These total daily doses are often divided and taken in two to four doses throughout the day. For example, a person weighing 75 kg (165 lbs) would take 15 mg per day.
It is crucial to exercise caution at higher body weights, as the cardiovascular system may not be prepared to handle a stimulatory agent like yohimbine.
Important Considerations
- Product Variability: Many supplements containing yohimbine either do not list how much yohimbine is included, or if they do, the actual dose ranges from 25-150% of the dose listed.
- Combining with Stimulants: When pairing yohimbine with other stimulatory agents, half-dose both supplements and work up to the recommended dose cautiously, as two supplements can interact negatively.
Risks and Side Effects
Clinical trials report few serious adverse reactions. However, case reports exist of rash, lupus-like syndrome, bronchospasm, arrhythmias, and death associated with yohimbine consumption. Increased anxiety, irritability, and excitability have also been reported.
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Animal studies suggest yohimbine may increase motor activity and seizures at higher dosages, may cause CNS stimulation and paralysis, and may precipitate psychoses in predisposed individuals. Signs of yohimbine toxicity include severe hypotension, dysrhythmia, heart failure, and death.
Common side effects reported at therapeutic doses include anxiety, nervousness, insomnia, increased heart rate, and elevated blood pressure. Gastrointestinal issues like nausea and vomiting have also been reported.
Yohimbine has been recognized as a product with possibly harmful cardiovascular effects, such as hypertension due to increased norepinephrine via alpha2-adrenergic receptor antagonism, and may be harmful in patients with heart failure.
Contraindications
This drug should not be used in the presence of renal or hepatic dysfunction.
Patients with kidney disease, peptic ulcer or pregnant or breast-feeding women should not use yohimbe.
Drug Interactions
Yohimbine may interact with several medications:
- Antianxiety agents: Yohimbine may diminish the therapeutic effect of antianxiety agents.
- Antihypertensive agents: Herbal products with blood pressure increasing effects may diminish the antihypertensive effect of antihypertensive agents.
- Iobenguane radiopharmaceutical products: Yohimbine may diminish the therapeutic effect of iobenguane radiopharmaceutical products.
- Brimonidine: The active ingredients in yohimbine can block the actions of brimonidine in certain human tissues, thus reducing the drug’s beneficial effects.
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.
Precautions
- Pre-existing Conditions: People with a history of heart disease and high or low blood pressure should not take yohimbe. In addition, people with mental health conditions should not take yohimbe as it can interact with certain types of antidepressant medications.
- Pregnancy and Children: Pregnant people and children under the age of 18 years should also refrain from using yohimbe.
- Surgery: This product may be unsafe when used before surgery or other medical procedures. It is important to fully inform your doctor about the herbal, vitamins, mineral or any other supplements you are taking before any kind of surgery or medical procedure.
Yohimbine for Erectile Dysfunction
Yohimbine has been investigated for use in treatment of sexual dysfunction. It may act by adrenergic blockade of alpha-2-adrenergic receptors in the corpus cavernosum and centrally in the serotonergic system.
A number of meta-analyses published before the American Urological Association (AUA) guidelines were conducted on older clinical trials, all concluding that yohimbine was more effective than placebo in treating erectile dysfunction in most, but not all, men.
The American Urological Association (AUA) guidelines on the management of erectile dysfunction (2005) states that yohimbine is not recommended for the treatment of erectile dysfunction based on review of data and panel consensus.
A Case for Depression
Historically, yohimbe bark was used in western Africa for fevers, leprosy, and coughs.
Yohimbe has traditionally been used to treat people with depression. Yohimbine inhibits monoamine oxidase (MAO) and therefore may be beneficial in depressive disorders.
One report studied depressed people who had not responded to fluvoxamine. When 5 mg of yohimbine was added three times each day, there was significant improvement. Some people required higher amounts of yohimbine before their depression improved.