Overview of disorders of sedating antihistamine use

Oral sedating antihistamines are sometimes used in a way that does not align with the directed use (nonmedical use)Australian Institute of Health and Welfare (AIHW)McNeely, 2014. For example, a person may use sedating antihistamines to treat a symptom other than the clinician intended, or to become intoxicated. Nonmedical use can apply to sedating antihistamines used alone, in compound preparations (eg cough and cold preparations), or as part of a disorder of polysubstance use (use of more than one substance)Algarni, 2021Schifano, 2021. Sedating antihistamines available in Australia include alimemazine (trimeprazine), brompheniramine, chlorphenamine, cyclizine, cyproheptadine, dexchlorpheniramine, dimenhydrinate, diphenhydramine, doxylamine and promethazine.

The spectrum of substance use is described in these guidelines by the terms ‘hazardous use’, ‘harmful use’ or ‘substance dependence’, outlined in Terminology describing the spectrum of substance use. Hazardous or harmful use of sedating antihistamines occurs most often; dependent use is rare. Prolonged daily use of recommended doses is most commonRoussin, 2013, and is seen in people seeking to manage conditions such as anxiety, insomnia, chronic itch or cravings for other substances.

The harmful effects of sedating antihistamine intoxication include fatal sedation, seizures, delirium and anticholinergic toxidrome and possibly serotonergic toxidrome with some antihistamines1Foong, 2018Oyekan, 2021The Royal Children's Hospital Melbourne (RCH). These effects are increased by concurrent use of other sedating substances (eg opioids, benzodiazepines, alcohol).

For advice on the management of sedating antihistamine toxicity, see Antihistamine poisoning: sedating antihistamines.

1 The antihistamine cyproheptadine is used in the treatment of serotonergic toxidrome.Return