α2-blockers are a subset of the alpha blocker class of drugs and are antagonists to the α2 adrenergic receptor. They are mainly used in research, finding limited clinical application in human medicine.
Historically, yohimbine was used as an aphrodisiac, and is still sometimes used in veterinary medicine (although now largely replaced by atipamezole) for reversing the effects of alpha-2 agonists such as medetomidine which are used as sedatives during surgery. 
α2-blockers have found medical uses in treating depression; the tetracyclic antidepressants mianserin and mirtazapine are α2-blockers, although their efficacy as antidepressants may come from their activity at other receptor sites.
Mechanistically, α2-blockers significantly increase adrenergic, dopaminergic and serotonergic neurotransmitters, and induce insulin secretion and decreases blood sugar levels.
Withdrawal from α2-blockers can be difficult or dangerous as the global down regulation of neurotransmitters may cause symptoms of depression and other neurological problems, and increased blood sugar levels together with decreased insulin sensitivity can cause diabetes. Reduced microcirculation together with adrenaline supersensitivity in organs such as liver can also be difficult problem when withdrawing from adrenergic blockers.
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