Yohimbe (Pausinystalia johimbe)

Yohimbe refers to the bark of Pausinystalia johimbe, a West‑African evergreen tree whose bark contains the alkaloid yohimbine. The extract is most often marketed as a dietary supplement and is principally used to modulate sympathetic nervous‑system activity, which can affect cardiovascular tone, blood flow, and sexual function.

• Sexual function: Controlled trials show yohimbine (5–10 mg/day) can improve erectile rigidity and increase libido in men with mild erectile dysfunction, likely via enhanced penile blood flow.
• Weight management & metabolic health: Acute dosing (0.2 mg/kg) modestly raises resting metabolic rate and promotes lipolysis, supporting modest weight‑loss adjunct use.
• Exercise performance: Small‑scale trials report increased aerobic capacity and reduced perceived exertion during moderate‑intensity exercise, attributed to heightened catecholamine release.
• Cognitive & mood effects: Limited data suggest low‑dose yohimbine may improve attention and reduce fatigue, but effects are modest and highly individual.
  All benefits are dose‑dependent and more robust in short‑term, well‑controlled studies; long‑term efficacy remains uncertain.

Yohimbine is a competitive antagonist of the α₂‑adrenergic receptor (α₂A, α₂B, α₂C). By blocking these inhibitory receptors on presynaptic sympathetic nerve terminals, yohimbine disinhibits norepinephrine release, increasing circulating catecholamines. Elevated norepinephrine stimulates β‑adrenergic receptors in adipocytes, activating hormone‑sensitive lipase and promoting free‑fatty‑acid mobilization. In penile tissue, the rise in nitric‑oxide synthase activity and cGMP production produces vasodilation, enhancing blood flow. Yohimbine also modestly blocks serotonin (5‑HT₁A) and dopamine D₂ receptors, which may contribute to its central stimulant and mood‑modulating effects. Its pharmacokinetics show rapid absorption (peak 30–60 min) and a half‑life of 2–3 h, metabolized primarily by CYP2D6.

Yohimbine (C₂₁H₂₆N₂O₃) is a indole alkaloid belonging to the β‑carboline family. IUPAC name: (2S,3R,12bR)-13‑Methoxy‑12‑hydroxy‑5,6‑dihydro‑2‑hydroxy‑1,3‑dihydro‑β‑carboline (common synonym: yohimbine hydrochloride when in salt form). The molecule features a fused indole‑pyridine core with a methoxy group at C‑13, a hydroxyl at C‑12, and a tertiary amine (pKa ≈ 9.5). The alkaloid is lipophilic (logP ≈ 2.5), poorly water‑soluble, and stable under acidic conditions but degrades in alkaline environments. The hydrochloride salt improves aqueous solubility for oral formulations.

Yohimbe bark is harvested from mature P. johimbe trees primarily in Cameroon, Gabon, and the Democratic Republic of Congo. Sustainable harvesting requires ≥30‑year‑old trees and a rotational harvest to avoid over‑exploitation. Extraction typically uses ethanol or methanol under controlled temperature to preserve yohimbine content (≈2–3 % w/w in raw bark). Commercial supplements use standardized extracts (10 % yohimbine HCl) produced via liquid‑liquid extraction and subsequent crystallization. Quality considerations include verifying yohimbine content by HPLC, testing for heavy metals, microbial contamination, and confirming botanical identity through DNA barcoding. Certified Good Manufacturing Practice (cGMP) facilities and third‑party testing (e.g., USP, NSF) are essential to ensure potency and safety.