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Yohimbine (), also known as quebrachine, is an indole alkaloid derived from the bark of the African tree Pausinystalia johimbe (yohimbe); also from the bark of the unrelated South American tree Aspidosperma quebracho-blanco. Yohimbine is an α2-adrenergic receptor antagonist, and has been used in a variety of research projects. It is a veterinary drug used to reverse sedation in dogs and deer.
While yohimbine behaves as an aphrodisiac in some mammals, it does not do so in humans. It has been prescribed as a treatment for erectile dysfunction, although its reported clinical benefits were modest and it has largely been superseded by the PDE5 inhibitor class of drugs. Substances that have purported to be extracts from the yohimbe tree have been marketed as dietary supplements for various purposes, but they contain highly variable amounts of yohimbine, if any; no published scientific evidence supports their efficacy.
Yohimbine has been largely superseded by the PDE5 inhibitor drugs such as sildenafil (Viagra). Prescriptions for it are now rare, and most US pharmaceutical manufacturers have discontinued production of prescription capsules and tablets.
Yohimbe is the common English name for the tree species P. johimbe (also called Corynanthe johimbe) and, by extension, the name of a medicinal preparation made from the bark of that tree, sold as an aphrodisiac. Oxford English Dictionary Online, article "Yohimbe", senses 1 and 2, respectively; Merriam-Webster Online, article "Yohimbe", first and second senses, respectively. In contrast, yohimbine is a pure alkaloid that can be isolated from yohimbe bark.
Yohimbine is just one of at least 55 indole alkaloids that have been isolated from the bark; and, while it has been described as the most active of these, it constitutes only 15% of the total alkaloid content. Others include rauwolscine, corynanthine and ajmalicine; the bark also contains non-alkaloids about which virtually nothing is known.
Yohimbe, thus a complex mixture, has been studied far less thoroughly than yohimbine, the pure compound. Pharmaceutical grade yohimbine is usually presented as the hydrochloride, which is more soluble.
One study found that samples of brands sold in American brick-and-mortar stores contained highly variable amounts of yohimbine, and sometimes none at all. Labelling claims were often misleading. Similar results have been reported by other laboratories for products sold in the US, in other countries and on the internet. One study found that many brands of "yohimbe" might not derive from the P. johimbe tree in the first place.Cohen et al, 368. (Samples did not include other alkaloids characteristic of P. yohimbe.) According to yet another source, the yohimbe sold in markets in West Africa, where the tree grows, is frequently adulterated with other species of the genus Pausinystalia; these contain little yohimbine. (2025). 9789290814955, PROTA Foundation. ISBN 9789290814955 The amounts of alkaloid found even in genuine P. johimbe bark vary considerably, depending on the source of the bark (roots, stem, branches, height, etc.).
Some brands sold over-the-counter were found to contain more yohimbine per serving than a standard pharmaceutical dose; yet, in the US, pharmaceuticals are subject to the strict regulatory regime pertaining to medicines. It is illegal to introduce or deliver "drugs" into interstate commerce without the permission of the US Food and Drug Administration (FDA). The FDA has asserted that some yohimbine-containing products are "drugs" because they are so promoted as to show "they are intended for use in the cure, mitigation, treatment or prevention of disease": 21 U.S.C. § 321(g)(1)(B).E.g. However the legal position is not entirely straightforward, and as of 1 February 2019 there does not appear to be any record of a successful prosecution.
Because of the lack of reliable scientific data on yohimbe, the European Food Safety Authority Panel on Food Additives determined that it was not possible to conclude on its safety or to establish a health-based guidance value. They wrote:
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Yohimbine selectively blocks the pre-synaptic α2-adrenergic receptors. Blockade of post-synaptic α2-adrenergic receptors causes only minor corpus cavernosum smooth muscle relaxation, due to the fact that the majority of adrenoceptors in the corpus cavernosum are of the α1 type. Blockade of pre-synaptic α2-adrenergic receptors facilitates the release of several neurotransmitters in the central and peripheral nervous system—thus in the corpus cavernosum—such as nitric oxide and norepinephrine. Whereas nitric oxide released in the corpus cavernosum is the major vasodilator contributing to the erectile process, norepinephrine is the major vasoconstrictor through stimulation of α1-adrenergic receptors on the corpus cavernosum smooth muscle. Under physiologic conditions, however, nitric oxide attenuates norepinephrine vasoconstriction.
It has also been studied as a potential treatment for erectile dysfunction, but there is insufficient evidence to rate its effectiveness. It is illegal in the United States to market an over-the-counter product containing yohimbine as a treatment for erectile dysfunction without getting FDA approval to do so. Nevertheless, the quantity of yohimbine in dietary supplements, often advertised as promoting sexual function, has been found to overlap with prescription doses of yohimbine.
Research on yohimbine, while confirming that it behaves as an aphrodisiac in animals, including rats, dogs and golden hamsters, has failed to do so in humans. According to researcher Joseph M. Betz in a 2010 encyclopedia article:Dr Betz was described as "a leading P. johimbe expert" by Cohen et al, 357. In 2018 he was appointed acting director of the Office of Dietary Supplements of the. NIH:
Around the year 2000, Cameroon was shipping P. johimbe to Europe at the rate of about 100 tonnes annually. Most bark is collected illegally by local people who are paid 150 per kilo (about US$0.10 per pound) for delivery of pre-dried bark at the roadside. In practice they confuse and mix it with P. macroceras ("false yohimbe"), a species that contains little yohimbine. (2025). 9781853838712, Earthscan Publications Ltd. ISBN 9781853838712
In its bark an alkaloid is found which was given the name Quebrachine. In 1914, two scientific papers claimed quebrachine was chemically identical to yohimbine. This was disputed, and the matter long remained in doubt.. ('Quebrachine' and 'yohimbine' had different effects on the heart in the dog model; but the suppliers of those reagents were trusted to vouch for their authenticity.) However, in 1972, Effler and Effler using modern analytical techniques, including mass spectrometry, UV absorption, IR absorption, and NMR, established that quebrachine and yohimbine are one and the same thing. They wrote:
A range of secondary reference works give 'quebrachine' as a synonym for yohimbine. (2025). 9783642603679, Springer Science & Business Media. ISBN 9783642603679
(1995). 9780815109921, Mosby, Incorporated. ISBN 9780815109921
(2025). 9780080488790, Elsevier. ISBN 9780080488790
(2025). 9781118135150, John Wiley & Sons. ISBN 9781118135150
(2025). 9780323172264, Elsevier Health Sciences. ISBN 9780323172264
(1965). 9780080865324, Academic Press. ISBN 9780080865324
(2025). 9781118685907, John Wiley & Sons. ISBN 9781118685907
(2025). 9780471471288, Wiley. ISBN 9780471471288.
Strictly speaking, wrote George Barger, yohimbine should have been given the scientific name quebrachine, seeing that it was first isolated from the quebracho tree and first named in the scientific literature. However the later work on P. yohimbe was better known, so the newer name stuck.
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