Esmirtazapine (ORG-50,081) is a drug which was under development by Organon for the treatment of insomnia and vasomotor symptoms (e.g., hot flashes) associated with menopause. As of 2009 it is in phase III clinical trials. Esmirtazapine is the (S)-(+)-enantiomer of mirtazapine and possesses similar overall pharmacology, including inverse agonist actions at H1 and 5-HT2 receptors and antagonist actions at α2-adrenergic receptors. As of March 2010, Merck terminated internal clinical development program for esmirtazapine, for hot flashes and insomnia, for strategic reasons.