Yohimbe

Scientific Name(s): Pausinystalia yohimbe (K. Schum.) Pierre ex Beille. Synonymous with Corynanthe johimbe . Family: Rubiaceae.

Common Name(s): Yohimbe , yohimbehe , yohimbine .

Clinical Overview

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Uses of Yohimbe

Yohimbe has been used in the treatment of organic and psychogenic impotence and for use as an aphrodisiac.

Yohimbe Dosing

Refer to manufacturer's recommendations.

Contraindications

This drug should not be used in the presence of renal or hepatic disease.

Pregnancy/Lactation

Do not use during pregnancy or lactation.

Yohimbe Interactions

None well documented.

Yohimbe Adverse Reactions

May cause severe hypotension, hypertension, abdominal distress, and weakness.

Toxicology

Yohimbe may cause central nervous system stimulation and paralysis and may precipitate psychoses in predisposed individuals.

Botany

Yohimbe is a tall evergreen tree that grows throughout the African nations of Cameroon, Gabon, and The Democratic Republic of the Congo. 1

History

The bark of the West African yohimbe tree is rich in the alkaloid yohimbine, and the crude bark and purified compound have been considered as aphrodisiacs. The bark has been smoked as a hallucinogen and has been used in traditional medicine to treat angina and hypertension. The drug has been investigated for the treatment of organic or psychogenic impotence. 2

Chemistry

The alkaloid yohimbine also is obtained from Aspidosperma quebracho-blanco and Rauwolfia serpentina . Authentic bark may contain up to 6% total alkaloids of which 10% to 15% are yohimbine. Other minor indole alkaloids include corynantheidine and allo-yohimbine. A comparison of chromatograms of extracts of authentic P. yohimbe bark with those of commercial products containing yohimbine found that many products contained measurable quantities of the alkaloid yohimbine but had very little of the other alkaloids previously reported in the species. Concentrations of yohimbine in the commercial products ranged from less than 0.1 to 489 parts per million (ppm) compared with 7,089 ppm in the authentic material. 3

Yohimbe Uses and Pharmacology

The crude drug and purified alkaloid have been used as an aphrodisiac and hallucinogen. Studies suggest that the drug may be effective in the treatment of male organic impotence. There are 3 double-blind, randomized, control trials using yohimbe to help reduce body weight; however, the results are conflicting and it is unclear whether yohimbine is effective. 1

Yohimbine is generally classified as an alpha-2-adrenergic blocking agent. Small doses have a stimulant action in humans resulting in autonomic and psychic changes commonly associated with the subjective experience of anxiety. Yohimbine has been reported to be an inhibitor of monoamine oxidase but more likely has a weak calcium channel blocking effect. 4 , 5 , 6

Yohimbine dilates blood vessels, thereby lowering blood pressure; however, its use as an antihypertensive agent has been abandoned. The drug causes a significant increase in blood pressure after an oral dose of 5 mg in patients with orthostatic hypotension secondary to pure autonomic failure or multisystem atrophy. This response is associated with an increased heart rate and increased plasma norepinephrine levels.

Because yohimbine can cause the dilation of peripheral and mucous membrane blood vessels along with central nervous system stimulation, the drug has been investigated for the treatment of organic impotence.

One older prescription product ( Afrodex , Bentex Pharmaceuticals) combined 5 mg each of yohimbine hydrochloride, methyltestosterone, and nux vomica in a capsule for the treatment of male climacteric and impotence. Although a number of clinical trials were conducted with this product, the results were generally unimpressive. 7 , 8

Investigations suggest that higher doses of the drug (6 mg 3 times/day) may be effective in the treatment of organically impotent men. One study found that 10 of 23 men treated with the drug derived a benefit from treatment. Eleven of the 23 men were diabetics. One prescription product containing 5.4 mg yohimbine hydrochloride is indicated as a sympathicolytic and mydriatic that also may have activity as an aphrodisiac. Yohimbine appears to be effective and may exert its activity by increasing the norepinephrine content of the corpus cavernosum. 9 , 10 , 11

In a double-blind, randomized, placebo-controlled, 8-week clinical trial, yohimbine was more effective than placebo in men with nonorganic erectile dysfunction. Eighty-six subjects were given 30 mg of yohimbine hydrochloride daily (two 5 milligram tablets 3 times/day) for 8 weeks. Efficacy was evaluated by subjective criteria that included sexual desire, sexual satisfaction, quality of erection or penile rigidity during sexual contact or intercourse, and frequency of sexual contacts. Objective response to yohimbine was based on improvement in penile rigidity by use of polysomnography. Significantly more subjects in the yohimbine group (71%) than the placebo group (45%) responded to treatment. No serious adverse events were reported and only 7% of patients reported tolerability of fair to poor. 12

In a meta-analysis of 7 randomized, double-blind, placebo-controlled trials involving male erectile dysfunction, yohimbine was found superior to placebo (odds ratio 3.85, 95% CI 6.67 to 2.22). Only randomized, placebo-controlled, double-blind trials of yohimbe monotherapy for erectile dysfunction were included. All studies evaluated found a positive response to yohimbine vs placebo and few adverse events were reported. 13

Yohimbine may help prevent neurally mediated syncope by increasing sympathetic tone (increase in norepinephrine) and muscle sympathetic nerve activity.

Yohimbine significantly improved hemodynamic and sympathetic tilt response in 7 out of 8 neurally mediated syncope patients. Patients experienced an upright tilt at 15-degree intervals every 3 minutes until reaching 75 degrees. Patients were placed supine if presyncope or syncope developed. Blood samples of plasma catecholamines were obtained during tilting and immediately after syncope or presyncope. Patients were allowed to rest for 45 minutes then were administered clonidine or yohimbe (dose varied for each drug). Tilting was repeated after subjects had been supine for 3 hours. Patients developed a significant decrease in blood pressure resulting in syncope between 45 and 75 degrees. Yohimbine increased norepinephrine ( P < 0.05), epinephrine ( P value not provided), muscle sympathetic nerve activity ( P < 0.01), systolic blood pressure ( P < 0.02), diastolic blood pressure ( P < 0.01), and heart rate ( P < 0.02) in neurally mediated syncope patients compared with baseline. 14

Dosage

Numerous dosing regimens available; therefore, follow manufacturer's directions.

Pregnancy/Lactation

Do not use during pregnancy or lactation.

Interactions

It has been suggested that yohimbine interacts with tricyclic antidepressants, central alpha-adrenergic drugs, centrally acting sympathomimetics, MAO inhibitors, and antimuscarinic drugs. 15 , 16 However, clinical documentation is lacking.

Adverse Reactions

The drug may cause severe hypotension, hypertension, abdominal distress, and weakness.

In 1 case report, an African American male 42 years of age suffered from a generalized erythrodermic skin eruption, progressive renal failure, and lupus-like syndrome following treatment with yohimbine. There is also a case report of yohimbine-induced bronchospasm. 17 , 18

Toxicology

Yohimbine may be toxic if ingested in high doses. Numerous case reports are documented in the scientific medical literature. Large doses may cause central nervous system stimulation and paralysis. Yohimbine may precipitate psychoses in predisposed individuals.

Bibliography

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