11-hydroxy yohimbine

11-Hydroxy Yohimbine: An Encyclopedic Reference

1. Identity: Chemical Names, Structure, and Natural Source

Chemical Identity

11-Hydroxyyohimbine has the molecular formula C₂₁H₂₆N₂O₄ and is registered in PubChem under Compound ID (CID) 183814. It carries the CAS Registry Number 140405-13-6 and the UNII identifier 1T5DRZ63HS, as recorded in the NIH NCATS Inxight Drugs database. Its IUPAC-derived systematic name, as reflected in ChemSpider ID 159837, is methyl (16α,17α)-11,17-dihydroxyyohimban-16-carboxylate.

The parent compound, yohimbine, provides the structural scaffold from which 11-hydroxyyohimbine is derived. Yohimbine is a pentacyclic monoterpenoid indole alkaloid with a molecular weight of 354.44 g/mol, whose core structure consists of a 17-α-hydroxyyohimban-16-α-carboxylic acid methyl ester, biosynthetically derived from the precursors tryptophan and the secoiridoid monoterpene secologanin. This intricate chemical structure features five chiral centers and two nitrogen atoms, which contributes to the diversity of yohimbine stereoisomers. 11-Hydroxyyohimbine differs from yohimbine (C₂₁H₂₆N₂O₃) by the addition of a single hydroxyl group at the C-11 position on the aromatic indole ring, yielding a molecular formula of C₂₁H₂₆N₂O₄—one additional oxygen atom relative to the parent molecule.

Synonyms and Other Names

• 11-OH-yohimbine
• 11-OH-YO
• 11-hydroxyyohimbine (no hyphen)
• Methyl (16α,17α)-11,17-dihydroxyyohimban-16-carboxylate

Natural Source and Botanical Origin

11-Hydroxy yohimbine is a naturally occurring alkaloid found primarily in the bark of the Pausinystalia yohimbe tree, native to West Africa. Yohimbe is one of a number of Corynanthe evergreen species growing in West and Central Africa in lowland forests. The tree grows about 30 m tall, with a straight bole, and its bark is grey to reddish-brown, with longitudinal fissures. The plant belongs to the family Rubiaceae and is also referenced in scientific literature under the synonymous name Pausinystalia johimbe or Corynanthe johimbe.

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. Analyses of yohimbe bark indicate that the average total indole alkaloid content is approximately 3–6%, with approximately 10–15% of the alkaloids being yohimbine; in addition to yohimbine and its isomers (α-yohimbine, β-yohimbine, allo-yohimbine), these alkaloids include ajmaline, dihydroyohimbine, corynantheidine, dihydrocorynantheine, and corynanthine (rauhimbin).

The yohimbine content in the bark is given as 7–115 mg/g and is usually around 10 mg/g. 11-Hydroxyyohimbine is not quantitatively the dominant alkaloid in the raw bark but is, as described in the pharmacology literature below, the primary human metabolite of yohimbine formed in vivo. It is also encountered in the bark as a minor constituent and can be produced through biotransformation of yohimbine. Several yohimbine-type indole alkaloids can be transformed into more polar products by fermentation with certain species of fungi and Streptomyces; methods of detection and isolation were developed for products produced in substantial yield; without exception the transformations represented monohydroxylation; and 11-hydroxy-yohimbine was among those isolated and characterized.

Yohimbine is an alpha-2 adrenoceptor antagonist and an indole alkaloid found in numerous botanical sources. It is the predominant alkaloid in extracts from the bark of the Pausinystalia yohimbe tree, and can also be found in Rauwolfia root. By extension, 11-hydroxyyohimbine, as a hydroxylated yohimbine derivative, would be expected to be associated with similar botanical sources wherever yohimbine itself is present.

Common Forms and Preparations

In the context of dietary supplements and nutraceuticals, 11-hydroxyyohimbine is encountered primarily in two ways: (1) as a constituent of standardized yohimbe bark extracts or whole-bark powders, where it is present alongside yohimbine and the full complement of bark alkaloids; and (2) as a purified or semi-purified isolate added to combination supplement formulations. Pharmaceutical-grade yohimbine is usually presented as the hydrochloride salt, which is more soluble. The same approach may be applied to its hydroxylated metabolite. There is a lack of consistency in the composition of yohimbine supplements, particularly with regard to the presence and concentration of the active alkaloid; some supplements may contain yohimbe bark extract rather than pure yohimbine hydrochloride, and the alkaloid content in these extracts can fluctuate widely—inconsistency that poses significant challenges in determining accurate and reliable dosing.

2. Traditional and Historical Use

Historically, yohimbine and its derivatives, including 11-hydroxy yohimbine, have played a significant role in traditional African medicine. For centuries, indigenous healers utilized yohimbe bark infusions to address a variety of ailments, notably as an aphrodisiac and remedy for sexual dysfunction. Yohimbe comes from the bark of the Pausinystalia yohimbe tree, which grows naturally in the tropical regions of western Africa; standing up to 30 meters tall, these evergreen trees have been revered by indigenous populations for centuries, particularly in countries like Cameroon, Gabon, and Nigeria; traditionally, African healers would carefully strip the bark from these trees and prepare it through various extraction methods, primarily using it as a natural stimulant and aphrodisiac.

The bark and its preparations were also valued for reported energizing effects, thought to increase stamina and vitality, and were sometimes used to support overall well-being and resilience during periods of physical or emotional stress. Yohimbe bark is a traditional treatment for a variety of disorders in addition to the treatment of sexual disorders (i.e., erectile dysfunction). These uses include the treatment of dementia, diabetic complications (e.g., neuropathy), exhaustion, fevers, insomnia, leprosy, low blood pressure, obesity, and syncope.

Extracts from yohimbe bark are used in West African traditional medicine in the belief that it is a herbal tonic and aphrodisiac. In the early twentieth century, yohimbine's active principles began to garner attention in Western medicine, where they were studied and employed as treatments for erectile dysfunction and other circulatory conditions.

It is important to note a fundamental distinction regarding historical use: the traditional preparations were of whole yohimbe bark, typically as infusions or decoctions of the dried bark, rather than isolates of any single alkaloid such as 11-hydroxyyohimbine. The presence of 11-hydroxyyohimbine as a discrete entity within those traditional preparations was not recognized historically; it has only been characterized as a specific compound through modern chemical and pharmacological analysis. Consequently, historical traditions pertain to the use of yohimbe bark as a complex botanical matrix, within which 11-hydroxyyohimbine was one of dozens of alkaloid constituents.

3. Key Constituents, Active Compounds, and Mechanisms of Action

Relationship to Yohimbine and Its Metabolite Status

The most pharmacologically important fact about 11-hydroxyyohimbine is that it is the principal human metabolite of yohimbine. The major metabolic pathway of yohimbine involves hepatic oxidation, primarily mediated by cytochrome P450 enzymes, specifically CYP2D6 and CYP3A4. CYP2D6 plays a crucial role in the 11-hydroxylation of yohimbine, forming 11-hydroxyyohimbine, a pharmacologically active metabolite.

The biopharmaceutics of yohimbine (YO) and the pharmacokinetics of 10-hydroxy-yohimbine (10-OH-YO) and 11-hydroxy-yohimbine (11-OH-YO) were investigated in healthy subjects following i.v. (5 mg) and oral (8 mg) dosing. The overall renal excretion of YO, 10-OH-YO, and 11-OH-YO, expressed as percent of the dose of YO administered, were not different following i.v. and oral dosing, and were around 0.1, 0.2, and 14%, respectively. This indicates that 11-OH-yohimbine is the quantitatively dominant urinary metabolite of yohimbine in humans, accounting for approximately 14% of the administered dose in urine alone—a figure consistent with it being the principal biotransformation product.

Yohimbine is hydroxylated to 11-hydroxy-yohimbine, and this is achieved above all through cytochrome P450 2D6 (CYP2D6). In vivo, the extent of yohimbine metabolism is determined by the CYP2D6 and CYP3A4 genotypes.

Pharmacokinetics of 11-Hydroxyyohimbine

Only a small amount of yohimbine hydrochloride and the active metabolite 11-hydroxyyohimbine is detectable in cerebrospinal fluid. Two hydroxyl metabolites could be determined: 10-hydroxyyohimbine and the active metabolite 11-hydroxyyohimbine.

The active metabolite 11-hydroxyyohimbine has a higher elimination half-life of about 6 hours, contrasting with the much shorter half-life of yohimbine itself. The overall renal excretion was around 14% for 11-OH-YO following dosing; following i.v. dosing of YO, the mean apparent terminal half-life of 11-OH-YO (347 ± 63 min) was almost four times higher than that of YO (91.0 ± 33.6 min), suggesting an elimi[nation rate-limited kinetic profile].

The kidneys excrete yohimbine and its metabolites, with less than 1% of the administered dose found unchanged in the urine after 24 hours. Yohimbine has a relatively short half-life of less than 1 hour, indicating rapid clearance from the plasma. The substantially longer half-life of 11-OH-yohimbine relative to its parent compound means that after oral ingestion of yohimbine (or yohimbe bark), 11-hydroxyyohimbine persists in systemic circulation considerably longer and may accumulate with repeated dosing.

Maximum plasma concentrations and area under the curve (AUC) of the active 11-OH-metabolite yohimbine were significantly lower in 10 elderly subjects (71.2 ± 3.5 years), compared with 11 young volunteers (26.3 ± 4.8 years), and 10 patients with Alzheimer's disease (69.5 ± 7.9 years). This age-related difference in metabolite exposure has not been fully characterized but may reflect changes in CYP2D6 enzyme activity across the lifespan.

Mechanism of Action: Alpha-2 Adrenergic Receptor Antagonism

The core mechanism shared by yohimbine and its metabolite 11-hydroxyyohimbine is antagonism of α₂-adrenergic receptors. The pharmacological activity of yohimbine is mediated by the combined action of the central and peripheral nervous systems. It selectively blocks the pre- and postsynaptic α₂-adrenergic receptors and has a moderate affinity for α₁ and α₂ subtypes.

The α₂-adrenoceptor antagonist capacities of two hydroxylated metabolites of yohimbine in man (10-OH-yohimbine and 11-OH-yohimbine) were investigated on the α₂-adrenoceptors of human platelets and adipocytes and compared to those of yohimbine. Yohimbine and 11-OH-yohimbine exhibited similar α₂-adrenoceptor affinity in biological studies, i.e. inhibition of adrenaline-induced platelet aggregation and inhibition of UK14304-induced antilipolysis in adipocytes.

These results show that the main hydroxylated metabolite of yohimbine in man (11-OH-yohimbine) possesses α₂-adrenoceptor antagonist properties. The discrepancies found in binding studies (i.e., 10-fold lower affinity of 11-OH-yohimbine than yohimbine for α₂-adrenoceptors but similar capacities in blocking biological α₂-adrenoceptor effects in cells) are attributable to the higher degree of binding of yohimbine to plasma protein. This finding is pharmacologically significant: although 11-OH-yohimbine shows lower binding affinity in radioligand displacement assays, its lower plasma protein binding allows it to exert a comparable free-fraction pharmacodynamic effect in intact biological systems.

Yohimbine and the two metabolites displaced [³H]-RX 821002 binding with equivalent affinities in platelet and adipocyte membranes with the following order of potency: yohimbine > 11-OH-yohimbine > 10-OH-yohimbine.

Being a derivative of indolylalkylamine, yohimbine selectively blocks α₂-adrenergic receptors. It weakens the negative feedback mechanism of norepinephrine release in nerve endings. When α₂-autoreceptors on presynaptic neurons are blocked, the inhibitory feedback on norepinephrine release is removed, resulting in increased norepinephrine output into the synapse and systemic circulation. This is the core mechanism underlying the diverse downstream effects of both yohimbine and 11-hydroxyyohimbine.

Yohimbine possesses a strong binding affinity for α₂ receptors with weak to moderate affinity for α₁-adrenergic receptors. It antagonizes α₂ receptors on presynaptic neurons, effectively obstructing norepinephrine binding.

Yohimbine also binds to other behaviourally relevant monoaminergic receptors in the following order: α-2 NE > 5HT-1A, 5HT-1B > 1-D > D3 > D2 receptors. Yohimbine displays marked affinity at human α_2A-, α_2B-, and α_2C-ARs, significant affinity for h5-HT_1A, h5-HT_1B, h5-HT_1D, and hD₂ receptors, and weak affinity for hD₃ receptors. In binding protocols, yohimbine exerts antagonist actions at α_2A-AR, h5-HT_1B, h5-HT_1D, and hD₂ sites, yet partial agonist actions at h5-HT_1A sites. Whether 11-hydroxyyohimbine replicates this full receptor-binding profile has not been verified in directly published human pharmacological experiments; the evidence for its receptor interactions is extrapolated from its demonstrated α₂-adrenoceptor activity.

The systemic effects of yohimbine influence multiple organ systems including cardiovascular, neuromuscular, endocrine, and nervous systems. The general implications of using yohimbine on the cardiovascular system are the increase in systolic blood pressure and increased blood flow, which when paired with the nervous system's increase in sympathetic nervous system stimulation, can lead to implications in exercise performance and feelings of alertness. Due to the norepinephrine spillover phenomenon, which is a trait of yohimbine ingestion, there is a dramatic increase in circulating norepinephrine and epinephrine, which can enhance neuromuscular control and alter fuel utilization for exercise performance.

4. Scientific Evidence by Area of Use

Note on scope: Direct human clinical trials of isolated 11-hydroxyyohimbine as a supplement are not represented in the peer-reviewed literature identified through systematic database search. The clinical evidence available pertains almost exclusively to yohimbine itself (the parent compound). Because 11-hydroxyyohimbine is the principal active human metabolite of yohimbine—and has been demonstrated to share its α₂-adrenoceptor antagonist mechanism—the clinical effects of orally administered yohimbine in humans are considered the most relevant and directly applicable evidence base for 11-hydroxyyohimbine's likely pharmacological activity in vivo. Evidence is characterized by strength throughout.

4.1 Erectile Dysfunction and Male Sexual Function

Yohimbine has been the most thoroughly studied natural agent for erectile dysfunction (ED), and its activity in this context is mediated at least in part through the generation of 11-hydroxyyohimbine in humans.

A systematic review and meta-analysis reviewed all randomized, placebo-controlled trials of yohimbine monotherapy for erectile dysfunction to determine its therapeutic efficacy. Seven trials fit the predefined inclusion criteria. Overall methodological quality of these studies was satisfactory. The meta-analysis demonstrated that yohimbine is superior to placebo in the treatment of erectile dysfunction (odds ratio 3.85, 95% confidence interval 6.67 to 2.22). Serious adverse reactions were infrequent and reversible.

A subsequent and larger systematic review and meta-analysis (Wibowo et al., 2021, Turkish Journal of Urology) identified eight eligible randomized controlled trials (RCTs) from 543 screened studies. Yohimbine alone (OR = 2.08, 95% CI 1.30–3.32, P = .002) and combined with other treatments (OR = 6.35, 95% CI 3.01–13.41, P < .001) showed a significantly greater probability of erectile function improvement compared to placebo. Yohimbine alone did not show a significant difference in the rate of improved sexual function (P = .07); however, the pooled results of both subgroups indicated a higher rate of improved sexual function (OR = 2.65, 95% CI 1.43–4.92, P = .002).

Doses studied in included trials were yohimbine 5 to 10 mg three times per day, or yohimbine hydrochloride 5, 5.4, or 6 mg given 3, 4, or 8 times per day, orally, for a period of 2 to 10 weeks for the treatment groups.

Evidence strength: Moderate. Multiple RCTs and two meta-analyses support yohimbine's superiority over placebo for erectile function improvement. However, sole administration of yohimbine and its combination with other supplements can improve erectile function in ED patients; however, it is not able to improve sexual function if not combined with other treatments for some endpoints. The trials are generally small, and effects are more consistent for psychogenic than organic ED. No trials have evaluated isolated 11-hydroxyyohimbine for this indication.

4.2 Body Composition and Fat Loss (Lipolysis)

Yohimbine has been investigated as a potential adjunct in weight management strategies due to its purported effects on metabolism and lipolysis. Its proposed mechanism involves antagonizing α₂-adrenergic receptors, which are involved in regulating fat breakdown. By blocking these receptors, yohimbine may increase noradrenaline release, thereby stimulating lipolysis and potentially promoting fat loss.

The most cited human clinical study in this area is a randomized, double-blind, placebo-controlled trial published in Research in Sports Medicine (Ostojic, 2006). The athletes (20 top-level male soccer players) were allocated to two randomly assigned trials. Subjects in the yohimbine group orally ingested tablets containing yohimbine at a dose of 20 milligrams per day in two equal doses for 21 days. Subjects in the placebo group ingested an equal number of identical-looking pills that contained cellulose. There were no statistically significant changes in body mass and muscle mass within or between trials (p > 0.05). 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 post-supplementation assessment (7.1 ± 2.2 vs. 9.2 ± 1.9%; p < 0.05). There were no changes in exercise performance indicators (bench and leg press, vertical jump, dribble and power test results, shuttle run) within or between trials (p > 0.05). No subject reported any side effects from yohimbine.

Not all human fat-loss studies have produced positive results. In a double-blind comparative study of the selective α₂-antagonist yohimbine in human obesity, 19 obese volunteers participated. Subjects were randomly allocated to the yohimbine group (n = 10, 18 mg yohimbine/day), or to the placebo group (n = 9). All subjects were maintained on a hypocaloric diet (1,000 kcal/day) during the 8 weeks of the study. There was no difference between the two groups with respect to either body weight, blood pressure, or heart rate during the different phases of the study.

The natural α₂ antagonist yohimbine promotes sympathetic activity by central as well as peripheral mechanisms. Administered prior to exercise, it boosts lipolysis and serum free fatty acid (FFA) levels both during and following exercise; blockade of adipocyte α₂ adrenoreceptors makes at least a modest contribution to this pro-lipolytic activity.

Evidence strength: Weak to moderate, mixed. The positive soccer-player trial (n = 20) is methodologically limited by small sample size, a highly trained population not representative of the general public, and lack of dietary control. The negative obesity trial (n = 19) found no effect in a sedentary, overweight population on a caloric restriction protocol. Overall, evidence for fat loss is promising but inconclusive. No trials isolating 11-hydroxyyohimbine's contribution to these effects have been conducted.

4.3 Cardiovascular and Noradrenergic Effects

Yohimbine has been shown to elevate blood levels of the catecholamines epinephrine and norepinephrine in healthy individuals, leading to increased heart rate, systolic blood pressure, and heightened alertness. This elevation in catecholamines can have a wide-ranging impact on the cardiovascular system and overall physiological arousal.

In a study on platelet function, the effect of the selective α₂-adrenergic receptor antagonist yohimbine on platelet aggregation was evaluated in healthy subjects. Yohimbine administered orally selectively antagonized epinephrine- but not collagen-, arachidonic acid-, or adenosine diphosphate-induced ex vivo platelet aggregation. The lowest dose of yohimbine that significantly inhibited epinephrine-induced platelet aggregation was 8 mg. The inhibitory effect of yohimbine on platelet aggregation lasted 10 hours with the 12 mg dose. Because 11-hydroxyyohimbine was established to share this α₂-adrenoceptor antagonist activity in the same platelet system, these effects are likely to be at least partially attributable to both compounds in vivo when yohimbine is administered orally.

Evidence strength: Moderate for yohimbine's cardiovascular and noradrenergic effects in pharmacological studies; effects of 11-hydroxyyohimbine per se on these endpoints have not been directly quantified in human trials.

4.4 Autonomic Nervous System and Norepinephrine Release

Central α₂-adrenergic receptors are expressed in noradrenergic neurons both presynaptically in the locus coeruleus (LC), where they control the inhibition of neurotransmitter release from presynaptic nerves, and pre- and mostly postsynaptically in the cortex, where they can modulate cellular signalling pathways. Blockade of these receptors by yohimbine and 11-hydroxyyohimbine therefore has implications for autonomic regulation, stress response, and central noradrenergic tone.

Yohimbine also enhances striatal dopamine (DA) turnover and suppresses striatal turnover of 5-HT. These broader monoaminergic effects mean that the pharmacological profile of yohimbine—and likely of 11-hydroxyyohimbine to a degree—extends beyond simple adrenergic antagonism to encompass interactions with serotonergic and dopaminergic neurotransmission.

Evidence strength: Established at the mechanistic/pharmacological level for yohimbine; extrapolated to 11-hydroxyyohimbine based on demonstrated shared α₂-antagonism. No dedicated human neuroimaging or neurotransmitter studies of 11-hydroxyyohimbine have been identified.

5. Body Systems and Health Areas Associated with 11-Hydroxyyohimbine

• Adrenergic/sympathetic nervous system: Primary site of action via α₂-adrenoceptor antagonism; modulation of norepinephrine release centrally and peripherally.
• Cardiovascular system: Effects on systolic blood pressure, heart rate, platelet aggregation, and peripheral blood flow through noradrenergic mechanisms.
• Adipose tissue/metabolic: Inhibition of antilipolytic α₂-adrenoceptors on adipocytes, with associated effects on free fatty acid release and lipid metabolism.
• Reproductive/urogenital system: Via yohimbine and its metabolites, α₂-adrenoceptor antagonism can increase peripheral vascular blood flow relevant to erectile physiology.
• Central nervous system: Modulation of locus coeruleus activity, noradrenergic, serotonergic, and dopaminergic tone; limited CNS penetration of 11-hydroxyyohimbine indicated by pharmacokinetic data.

6. Dosage Forms and Dosages Reported in Studies

No human clinical studies have specifically dosed isolated 11-hydroxyyohimbine as a standalone supplement. Dosage information available from the literature refers to yohimbine (the parent compound), from which 11-hydroxyyohimbine is generated metabolically.

Yohimbine Doses Used in Clinical Studies (Generating 11-OH-Yohimbine In Vivo)

• Pharmacokinetic studies of yohimbine and its hydroxylated metabolites in healthy subjects used i.v. (5 mg) and oral (8 mg) dosing.
• Clinical trials for erectile dysfunction used yohimbine 5 to 10 mg three times per day, or yohimbine hydrochloride 5, 5.4, or 6 mg given 3, 4, or 8 times per day, orally, for a period of 2 to 10 weeks.
• In the soccer-player body composition trial, subjects in the yohimbine group orally ingested tablets containing yohimbine at a dose of 20 milligrams per day in two equal doses for 21 days.
• In the obesity study, subjects received 18 mg yohimbine per day.
• Total daily dosages of 0.2 mg/kg body weight have been used in studies 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 150 lb (68 kg) person could take 7 mg twice daily to reach a total dose of 14 mg.

Dosage Form Considerations

An LC-MS/MS assay was developed and validated according to FDA guidelines to simultaneously quantify yohimbine and its main metabolite 11-OH-yohimbine in human plasma, demonstrating that 11-OH-yohimbine can be measured in plasma following oral yohimbine administration. Co-administration with the CYP2D6 inhibitor paroxetine (three-day intake of 20 mg) resulted in doubled maximum concentration of yohimbine, a tenfold increase of AUC, and fourfold prolonged elimination half-life—consequences that would also affect the generation and plasma levels of 11-OH-yohimbine.

The pharmacokinetics of yohimbine HCl vary widely from one individual to another. Regular administration of yohimbine HCl (three times daily for 6 days) had no effect on the pharmacokinetics.

7. Safety Considerations and Drug Interactions

Safety Profile of 11-Hydroxyyohimbine in the Context of Yohimbine

Because 11-hydroxyyohimbine is the primary pharmacologically active metabolite of yohimbine, its safety profile is inseparable from that of yohimbine. Yohimbine, a component of yohimbe, has been associated with cardiac arrhythmia (irregular heartbeat), blood pressure problems, heart attacks, and seizures. Because of inaccurate labeling and potential for serious side effects, yohimbe supplements have been restricted or banned in many countries. Yohimbe caused stomach problems, tachycardia (a rapid heartbeat), anxiety, and high blood pressure, according to a study comparing calls made to the California Poison Control System over a 7-year period. People calling about yohimbe were generally more likely to need medical care than other callers.

Though yohimbine is effective, side effects may include anxiety, nervousness, and an elevated heart rate, and the reported dose of yohimbine in many supplement formulas doesn't match the actual dose.

CYP2D6 Pharmacogenomics and Toxicity Risk

Genetic polymorphisms in CYP2D6 can significantly influence yohimbine metabolism, leading to substantial interindividual variability in its clearance and clinical effects. Individuals with certain CYP2D6 genotypes may exhibit impaired metabolism, resulting in higher plasma concentrations and an increased risk of adverse effects.

In a case series examining yohimbine intoxication in four individuals who ingested a yohimbine-containing drug powder, blood concentrations ranged from 249 to 5,631 ng/mL—a 22-fold difference despite a presumed uniform dose of 5 g. This variability was linked to the individuals' cytochrome P450 2D6 (CYP2D6) phenotypes, with decreased CYP2D6 activity increasing the risk of toxic yohimbine levels. All four patients were identified as phenotypic CYP2D6 intermediate metabolizers, contributing to their reduced metabolic activity and higher yohimbine concentrations.

These findings suggest that understanding a patient's CYP2D6 metabolic activity and phenotyping patients for CYP2D6 activity before initiating yohimbine treatment might be crucial for determining safe doses and minimizing overdose risk. For 11-hydroxyyohimbine specifically, individuals who are CYP2D6 poor metabolizers will produce less of this metabolite from yohimbine, whereas CYP2D6-extensive metabolizers will generate higher plasma concentrations of 11-OH-yohimbine more rapidly.

Drug Interactions

CYP2D6 substrate drugs: Yohimbine inhibits CYP2D6 and may therefore affect the intracellular concentration of drugs metabolized by these enzymes.

Antihypertensives: Yohimbine may diminish their effects. Bupropion: Co-ingestion with yohimbe products resulted in toxic effects.

Opioids: Yohimbine may cause withdrawal and anxiety symptoms.

Combining yohimbine with stimulants and CYP2D6 inhibitors may increase the risk of adverse effects.

Special Populations

Pregnant or nursing individuals: Yohimbine may cause serious side effects.

Individuals with cardiovascular, liver, or kidney disease may experience serious side effects. Yohimbine can raise blood pressure so taking it may compound the problem in those with hypertension. Those with psychiatric conditions including PTSD, anxiety, bipolar disorder, depression, mania, or schizophrenia may have their conditions worsened.

Maximum plasma concentrations and AUC of the active 11-OH-metabolite were significantly lower in elderly subjects compared with young volunteers and Alzheimer's disease patients; there is great variability in the plasma distribution of yohimbine; and clinical relevance of use in the elderly is not assessable.

Regulatory Status

Yohimbe sold as a dietary supplement may not work like the prescription medication that contains yohimbine. It is illegal in the United States to market an over-the-counter product containing yohimbine as a treatment for erectile dysfunction without getting approval from the FDA. Yohimbe bark and extract are used in manufactured dietary supplements, but there is inconclusive scientific evidence that they have an effect or are safe to use, as yohimbine levels may vary substantially among supplement products. Yohimbe bark extract is insufficiently characterized for its properties, and is possibly unsafe to consume.

Product Variability

Twelve commercial raw materials of yohimbe were analyzed by microscopic and UPLC-UV-MS methods. The study revealed that three samples were probably adulterated and four other samples contained various levels of impurities. Yohimbine was not detected in one sample, whereas its presence in other samples was found to be in the range 0.1–0.91%. The same analytical variability would be expected to apply to 11-hydroxyyohimbine content in bark-based products.

8. Summary of Evidence Strength

11-Hydroxyyohimbine occupies a unique position in the supplement and pharmacological literature: it is simultaneously a naturally occurring alkaloid minor constituent of yohimbe bark, and the predominant pharmacologically active human metabolite of yohimbine. Its α₂-adrenoceptor antagonist properties are established in controlled in vitro and ex vivo human cell systems. However, no independent human clinical trials have evaluated isolated 11-hydroxyyohimbine as a dietary supplement or drug. All clinical evidence for efficacy in sexual dysfunction, body composition, and related areas derives from studies of yohimbine itself, in which 11-hydroxyyohimbine was generated endogenously and contributed to observed effects. The extended half-life of 11-OH-yohimbine (~6 hours) relative to yohimbine (~0.6 hours) suggests it plays a sustained pharmacological role after oral yohimbine dosing, but its individual quantitative contribution to clinical outcomes has not been disaggregated from that of the parent compound in any published human trial. Evidence characterization: mechanistically supported but clinically unverified as an isolated agent.

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