Yohimbines

Yohimbines are a group of indole alkaloids that includes yohimbine and several related molecules. They occur naturally in the bark of Pausinystalia yohimbe and in smaller amounts in other plant species. The term yohimbines can refer to the parent compound or closely related alkaloids with similar pharmacological activity.

Pharmacology and mechanism: Yohimbines act as competitive antagonists of alpha-2 adrenergic receptors. By blocking these receptors, they increase the release of norepinephrine and sympathetic nervous system activity. This can produce effects such as increased heart rate, elevated blood pressure, pupil dilation, and enhanced lipolysis. Yohimbines can also exert central stimulant effects by acting on brain receptors.

Medical use and regulation: Yohimbine has been prescribed in some countries for erectile dysfunction, but the evidence is mixed and it is not widely recommended in many clinical guidelines. Regulation varies by country: it may be available as a prescription drug, as a regulated extract from yohimbe bark, or as an over-the-counter dietary supplement in some regions. Products marketed for weight loss or sexual enhancement have faced regulatory action due to safety concerns, quality control, and inconsistent labeling.

Safety and side effects: Common adverse effects include increased blood pressure, tachycardia, anxiety, insomnia, headache, dizziness, nausea, and sweating. More serious events such as fainting or cardiovascular complications have been reported, particularly at higher doses or with coadministration of stimulants or monoamine oxidase inhibitors. Yohimbines are contraindicated in certain cardiovascular conditions and during pregnancy; they should be used under medical supervision where required.

Chemistry and sources: Yohimbines are the principal active alkaloids derived from yohimbe, though related compounds exist. They are typically supplied as pharmaceutical yohimbine salts or standardized plant extracts.