Yohimbine is a potent and relatively nonselective alpha 2-adrenergic receptor (AR) antagonist, with IC50 of 0.6 μM. IC50 value: 0.6 uM [1] Target: alpha 2-adrenergic receptor in vitro: Yohimbine inhibits alpha2-receptor antagonist with Ki of 1.05 nM, 1.19 nM, and 1.19 nM for α2A, α2B, α2C, respectively. Yohimbine also inhibits 5-HT1B with Ki of 19.9 nM. Yohimbine acts to block the lowering of cAMP by alpha-2 adrenoceptor agonists. yohimbine actually causes a pronounced lowering of tyrosinase activity. [3] in vivo: Yohimbine is an antagonist at alpha2-noradrenaline receptors with putative panicogenic effects in human subjects, was administered to Swiss-Webster mice at doses of 0.5, 1.0, and 2.0 mg/kg. Yohimbine potentiates active defensive responses to threatening stimuli in Swiss-Webster mice.[2]