Selective histamine H1 antagonism: novel hypnotic and pharmacologic actions challenge classical notions of antihistamines.

Numerous "antihistamines" as well as various psychotropic medications with antihistamine properties are widely utilized to treat insomnia. Over-the-counter sleep aids usually contain an antihistamine and various antidepressants and antipsychotics with antihistamine properties have sedative-hypnotic actions. Although widely used for the treatment of insomnia, many agents that block the histamine H1 receptor are also widely considered to have therapeutic limitations, including the development of next-day carryover sedation, as well as problems with chronic use, such as the development of tolerance to sedative-hypnotic actions and weight gain. Although these clinical actions are classically attributed to blockade of the H1 receptor, recent findings with H1 selective agents and H1 selective dosing of older agents are challenging these notions and suggest that some of the clinical limitations of current H1-blocking agents at their currently utilized doses could be attributable to other properties of these drugs, especially to their simultaneous actions on muscarinic, cholinergic, and adrenergic receptors. Selective H1 antagonism is emerging as a novel approach to the treatment of insomnia, without tolerance, weight gain, or the need for the restrictive prescription scheduling required of other hypnotics.