Esmirtazapine (SCH 900265) is a drug which was under development by Organon for the treatment of insomnia and vasomotor symptoms (e.g., hot flashes) associated with menopause. 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 2-adrenergic receptors. Merck has terminated its internal clinical development program for esmirtazapine as of March 2010.