Esmirtazapine is a drug

Drug

A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

 which is under development by Organon

Organon International

Organon is a human pharmaceutical company headquartered in Oss, Netherlands. In November 2007 the company became a part of Schering-Plough Corporation, acquired Organon, active pharmaceutical ingredient producer Diosynth , and its veterinary pharmaceutical sister company Intervet from Akzo Nobel. ...

 for the treatment of insomnia

Insomnia

Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...

 and vasomotor

Vasomotor

Vasomotor refers to actions upon a blood vessel which alter its diameter. More specifically, it can refer to vasodilator action and vasoconstrictor action....

 symptom

Symptom

A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...

s (e.g., hot flashes) associated with menopause

Menopause

Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...

. As of 2009 it is in phase III clinical trial

Clinical trial

Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...

s. Esmirtazapine is the (S)-(+)-enantiomer

Enantiomer

In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...

 of mirtazapine

Mirtazapine

Mirtazapine is a tetracyclic antidepressant used primarily in the treatment of depression. It is also sometimes used as a hypnotic, antiemetic, and appetite stimulant, and for the treatment of anxiety, among other indications...

 and possesses similar overall pharmacology

Pharmacology

Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...

, including inverse agonist

Inverse agonist

In the field of pharmacology, an inverse agonist is an agent that binds to the same receptor as an agonist but induces a pharmacological response opposite to that agonist....

 actions at H₁

H1 receptor

The H1 receptor is a histamine receptor belonging to the family of Rhodopsin like G-protein-coupled receptors. This receptor, which is activated by the biogenic amine histamine, is expressed throughout the body, to be specific, in smooth muscles, on vascular endothelial cells, in the heart, and in...

 and 5-HT₂ receptor

5-HT2 receptor

The 5-HT2 receptors are a subfamily of 5-HT receptors that bind the endogenous neurotransmitter serotonin . The 5-HT2 subfamily consists of three G protein-coupled receptors which are coupled to Gq/G11 and mediate excitatory neurotransmission, including 5-HT2A, 5-HT2B, and 5-HT2C...

s and antagonist

Receptor antagonist

A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...

 actions at α₂-adrenergic receptor

Alpha-2 adrenergic receptor

The alpha-2 adrenergic receptor is a G protein-coupled receptor associated with the Gi heterotrimeric G-protein. It consists of three highly homologous subtypes, including α2A-, α2B-, and α2C-adrenergic. Some species other than humans express a fourth α2D-adrenergic receptor as well...

s. As of March 2010, Merck terminated internal clinical development program for esmirtazapine, for hot flashes and insomnia, for strategic reasons.