Yohimbine is a plant alkaloid with alpha-2-adrenergic blocking activity. Yohimbine has been used as a mydriatic and in the treatment of impotence. The exact mechanism for its use in impotence has not been fully elucidated. Yohimbine exerts antagonist actions at halpha(2A)-AR, h5-HT(1B), h5-HT(1D), and hD(2) sites, partial agonist actions at h5-HT(1A) sites. Yohimbine-mediated norepinephrine release at the level of the corporeal tissues may also be involved. In addition, beneficial effects may involve other neurotransmitters such as dopamine and serotonin and cholinergic receptors. Yohimbine has a mild anti-diuretic action, probably via stimulation of hypothalmic center and release of posterior pituitary hormone. Reportedly yohimbine exerts no significant influence on cardiac stimulation and other effects mediated by (beta)-adrenergic receptors. Its effect on blood pressure, if any, would be to lower it; however, no adequate studies are at hand to quantitate this effect in terms of Yohimbine dosage. Side effect of Yohimbine include anxiety, tremor, palpitations, diarrhea, and supine hypertension.

Dapiprazole is an alpha-1 adrenergic receptors antagonist which was developed for for the treatment of drug induced mydriasis produced by adrenergic or parasympatholytic agents. The drug was marketed under the name Rev-Eyes, however it was withdrawn from market due to its slow effect.

Guanabenz, an antihypertensive agent for oral administration-, is an aminoguanidine derivative, 2,'6-dichlorobenzylideneamina-guanidine acetate. It is white to an almost white powder having not more than a slight odor. Sparingly soluble in water and in 0.1 N hydrochloric acid; soluble in alcohol and in propylene glycol. Guanabenz is an orally active central alpha-2 adrenergic agonist. Its antihypertensive action appears to be mediated via stimulation of central alpha-adrenergic receptors, resulting in a decrease of sympathetic outflow from the brain at the bulbar level to the peripheral circulatory system. In clinical trials, guanabenz acetate, given orally to hypertensive patients, effectively controlled blood pressure without any significant effect on glomerular filtration rate, renal blood flow, body fluid volume or body weight. The Myelin Repair Foundation and the National Institutes of Health (National Institute of Neurological Disorders and Stroke) are developing guanabenz for the treatment of multiple sclerosis. Unlike the currently available treatment for multiple sclerosis that suppresses the immune system, guanabenz, an FDA approved the drug for the treatment of high blood pressure, has a potential to reduce the loss of myelin by protecting and repairing myelin-producing cells in the brain from damage. Phase I development is underway in the US.

Bretylium (bretylium tosylate) is an antifibrillatory and antiarrhythmic agent. Bretylium is abromobenzyl quaternary ammonium compound which selectively accumulates in sympathetic ganglia and their postganglionic adrenergic neurons where it inhibits norepinephrine release by depressing adrenergic nerve terminal excitability. The drug has a direct positive inotropic effect on the myocardium and blocking effect on postganglionic sympathetic nerve transmission. The drug is poorly absorbed orally, requiring either i.m. or i.v. administration.

AZAPETINE, a benzazepine derivative, is an alpha-1 adrenoceptor antagonist. It is a potent arterial vasodilator in the treatment of peripheral vascular diseases.

AZAPETINE, a benzazepine derivative, is an alpha-1 adrenoceptor antagonist. It is a potent arterial vasodilator in the treatment of peripheral vascular diseases.

Dihydroergocornine is an ergot alkaloid, one of the three components of ergoloid (trade name Hydergine). Dihydroergocornine (as the component of Ergoloid mesylates) has been used to treat dementia and age-related cognitive impairment (such as in Alzheimer disease), as well as to aid in recovery after stroke. There is no specific evidence which clearly establishes the mechanism by which Hydergine® (ergoloid mesylates) preparations produce mental effects, nor is there conclusive evidence that the drug particularly affects cerebral arteriosclerosis or cerebrovascular insufficiency. Hydergine may stimulates dopaminergic and serotonergic receptors and blocks alpha-adrenoreceptors.

Dihydroergocristine is an ergot alkaloid that has an partial agonist activity on dopaminergic and alpha-adrenergic receptors and antagonist activity on serotonin receptors. The drug was approved by FDA in combination with other alkaloids (dihydroergocornine, dihydro-alpha-ergocryptine and dihydro-beta-ergocryptine mesylate salts) under the name Hydergine for the treatment of dimentia and cerebrovascular insufficiency.

Methoxamine is an alpha-adrenergic agonist that induces prolonged peripheral vasoconstriction, and can also stimulate the release of arginine vasopressin in humans. In clinical trials, methoxamine was found to improve fecal incontinence. It had been marketed by Glaxo-Smith-Kline under the brand name Vasoxyl but has been discontinued. Methoxamine was also found to stimulate the induction of hiPSC-derived hepatoblasts to ALBUMIN+ cells.