Editing Hypnotic (section)

=== Antihistamines ===
{{Main|H1 antagonist}}
[[Antihistamine]]s, also known as H<sub>1</sub> antagonists, are a class of drugs that inhibit action at H<sub>1</sub> receptors. They are clinically used to alleviate allergic reactions including [[allergic rhinitis]], [[allergic conjunctivitis]], and [[urticaria]], which are mediated by [[histamine]].{{Citation needed|date=March 2025}} First-generation antihistamines, such as [[doxylamine]] and [[diphenhydramine]], often cause sedation as a side effect, which can be utilized to treat insomnia. Some antihistamines, such as doxylamine, are available for purchase [[over-the-counter]] (OTC) in some countries and can be used for the occasional relief of insomnia.<ref>{{Cite journal |last1=Culpepper |first1=Larry |last2=Wingertzahn |first2=Mark A. |date=2015 |title=Over-the-Counter Agents for the Treatment of Occasional Disturbed Sleep or Transient Insomnia: A Systematic Review of Efficacy and Safety |journal=The Primary Care Companion for CNS Disorders |volume=17 |issue=6 |doi=10.4088/PCC.15r01798 |issn=2155-7772 |pmc=4805417 |pmid=27057416}}</ref> Low-dose [[doxepin]] is approved by the FDA for the treatment of insomnia.<ref name=":1">{{Cite web |title=Pharmacotherapy for insomnia in adults |url=https://www.uptodate.com/contents/pharmacotherapy-for-insomnia-in-adults |access-date=2023-03-13 |website=www.uptodate.com}}</ref> Second generation of antihistamines such as [[cetirizine]] and [[loratadine]] have a much less sedating effect than the first ones with a much lower degree of crossing the [[blood–brain barrier]].<ref>{{Cite journal |last1=Slater |first1=J. W. |last2=Zechnich |first2=A. D. |last3=Haxby |first3=D. G. |year=1999 |title=Second-generation antihistamines: a comparative review |url=https://pubmed.ncbi.nlm.nih.gov/9951950/ |journal=Drugs |volume=57 |issue=1 |pages=31–47 |doi=10.2165/00003495-199957010-00004 |issn=0012-6667 |pmid=9951950 |s2cid=46984477}}</ref>

In common use, the term ''antihistamine'' refers only to compounds that inhibit action at the H<sub>1</sub> receptor.{{Citation needed|date=March 2025}}

Clinically, H<sub>1</sub> antagonists are used to treat certain [[Allergy|allergies]]. Sedation is a common side effect, and some H<sub>1</sub> antagonists, such as [[diphenhydramine]] and doxylamine, are also used to treat insomnia.{{Citation needed|date=March 2025}}