Yohimbe - Medicinal Uses, Interactions, Side Effects, Dosage
Yohimbe
Yohim be is the crude herbal product derived from the dried bark of Pausinystalia yohimbe, a West African evergreen tree. Yohim bine is the active chemical isolated from yohimbe, also found in smaller concentrations in the root of Rauwolfia.
Uses and Benefits:
Yohimbe bark was originally used in Africa as an aphrodisiac and to restore erections in impotent men. Crude yohimbe and the isolated chemical yohimbine are similarly used in Western countries to increase sexual desire and for erectile dysfunction. These products are also used in male "performance" supplements, and for fatigue, orthostatic hypotension, obesity, and clonidine overdose.
Pharmacology:
The bark of P. yohimbe contains up to 6% mixed indole alkaloids, of which yohimbine is the principal active constituent. Structurally related to reserpine, yohimbine has been well characterized as a selective alpha adrenergic receptor antago­nisp, Yohimbine readily enters the central nervous system (CNS), where it increases sympathetic outflow, potentiating the release of norepinephrine from sympathetic nerve terminals. These effects ac­tivate alpha and beta receptors in the heart and peripheral vascula­ture, with a consequent rise in heart rate and blood pressure. Theso actions are opposite to those of c1onidine, an alpha receptor ago· nist, which decreases sympathetic outflow. At high concentrations, yohimbine also inhibits monoamine oxidase (MAO) and acetyl­cholinesterase enzymes, and has other pharmacologic properties.
Yohimbine successfully stimulates sexual behavior in animal models. The most likely mechanisms include a direct CNS effect, and or a peripheral effect on alpha adrenergic receptors in penilo tissue that relaxes smooth muscle in the corpus cavernosum.
Clinical Trials:
Yohimbe, the crude herb, has not been studied clinically, However, yohimbine has been studied in many randomized, controlled trials, and a systematic review and meta-analysis evaluated the placebocontrolled trials published through early. Only moderate- to high-quality studies were included, and seven trials met criteria for yohimbine monotherapy. These trials contained 11 to 100 patients each, lasted from 4 to 10 weeks, and included patients with both organic and psychogenic impotence. The usual dose was 5-10 mg t.i.d. Outcome measures were not uniform among the studies, and included questionnaires of self­reported treatment success, objective rating scales, and penile tumescence monitoring.
All studies found that yohimbine was more effective than placebo; this reached statistical significance in five of the seven trials. Statistically significant results were found less often for pa­tients with identified organic etiologies. A meta-analysis of the studies also favored the drug over placebo, with a calculated overall odds ratio of 3.85 (95% confidence interval 6.67-2.22). Positive responders varied from 34% to 73% with yohimbine, and from 4% to 45% with placebo.
Despite these overall positive findings, three subsequent chronic trials of good quality found negative results. In one randomized, double-blind, placebocontrolled crossover study, 36 mg/day of yohimbine had identical findings to placebo in 29 patients with mixed-type impotence. In an unrandomized placebocontrolled trial, a large dose of 100 mg/day also had similar activity to placebo in 22 patients with organic erectile dysfunction. Lastly, a randomized, controlled crossover study of 5.4 mg t.i.d. (combined with isoxsuprine or pentoxifylline) found none of patients with vasculogenic erectile dysfunction to have a complete therapeutic response. In addition, no improvement was seen in arterial flow velocity or resistance indexes by penile duplex ultrasonography.
Yohimbine has been reported to have some success in con­trolled studies for treating autonomic orthostatic hypotension as an antidote for c10nidine overdose to reverse symptoms of dry mouth by increasing salivary flow and to decrease symp­lams of opiate withdrawal.
Adverse Effects:
In most of the clinical trials using usual doses of 5-10 mg t.i.d., adverse effects were observed in about 10-30% of patients, but were considered to be minor and well tolerated. These primarily included anxiety, headache, dizziness, nausea, tachycardia, and hypertension. In a clinical trial using an excessively large dose of 100 mg q.d., adverse effects were identified in 80% of patients compared to 20% of placebo controls. The most frequently reported side effects for yohimbine were increased urinary frequency (32%), tachycardia (27%), and anxiety (18%).
Yohimbine should be avoided in patients with hypertension; it has been associated with increased blood pressure in these patients, and with a case of hypertensive crisis. Based on its pharmacologic effects, yohimbine should also be avoided in patients with angina, claudication, or other cardiovascular diseases. Anxiety or an exacerbation of symptoms is more likely to occur in patients with psychiatric disorders such as panic attacks, posttraumatic stress disorder, and bipolar-affective disease.
Yohimbine has also been associated with isolated case reports of bronchospasm, agranulocytosis, and a lupus-like syndrome with renal failure; product contamination is also a possible cause of these disparate reports. Overdoses with several hundred milligrams have resulted in cardiovascular, gastrointestinal, and nervous system toxicities, with clinical outcomes ranging from benign to fatal.
Side Effects and Interactions:
Yohimbine antagonizes the antihypertensive properties of central alpha agonists such as clonidine and guanabenz, and the effects of yohimbine can similarly be reduced. Yohimbine may cause exaggerated cardiovascular and anxiety responses in patients concurrently taking psychiatric medications, especially tricyclic antidepressants that inhibit norepinephrine reuptake. These effects are not expected with selective serotonin reuptake inhibitors. Some authors have advised that yohimbine should nor be used concurrently with sympathomimetic drugs or tyramine containing foods, based on the herb's potential MAO inhibitor effects. These concerns are probably not warranted at usual therapeutic doses, and no interactions have been reported, However, it would be advisable to avoid yohimbine with other sympathomimetic drugs (including caffeine and other stimulants) duo to the potential for enhanced cardiovascular and CNS toxicity.
Cautions:
Due to lack of data and the potential for cardiovascular or CNS effects, yohimbine should generally be avoided in pregnant and breast-feeding women.
Preparations & Doses:
Yohimbine and yohimbe are widoly available herbal medicines as monopreparations or combined with many other herbs and supplements. The usual oral dose of yohimbine for erectile dysfunction is 5-10 mg t.i.d. Yohimbine is also available as an FDA-approved prescription drug (5.4-mg tablet as the HCI salt), marketed as a "sympatholytic and mydriatic," although actual pharmacologic effects may be quite different.
Summary Evaluation:
Yohimbine is widely used for erectile dysfunction and sexual potency. The results of randomized controlled clinical trials are gen­erally positive, especially for nonorganic etiologies, but study results are inconsistent and do not demonstrate efficacy beyond a reasonable doubt. Benefits, if any, appear to be mild; yohimbine is not expected to be as effective as sildenafil or other well-char­acterized pharmacologic therapies for erectile dysfunction. Side effects of usual doses of yohimbine appear to be well tolerated in selected patients in controlled studies, but adverse effects are dosedependent. There are also many potential and reported drug and disease interactions.
About the Author: Steve Mathew is a writer, who writes many great articles on herbal medicines for common ailments and diseases. For more information on herbal remedies and home remedies visit our site on health care.
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