OtherOTC sleep aidFirst-generation antihistamineAnticholinergic

Doxylamine

Also known as Unisom SleepTabs · Restavit · Diclegis/Diclectin component (with pyridoxine)

Written by enwyReviewed 5 Aug 20262 sources0 comments

First-generation sedating antihistamine sold OTC for insomnia (Unisom SleepTabs) and, with pyridoxine, for pregnancy nausea. Longer-acting and more sedating than diphenhydramine, with the same anticholinergic drawbacks and rapid tolerance.

01 Overview

Doxylamine is a first-generation ethanolamine H1 antihistamine widely used as an OTC hypnotic (brand Unisom SleepTabs). It is also combined with vitamin B6 (pyridoxine) in prescription products for nausea and vomiting of pregnancy, one of the few sleep-adjacent agents considered safe in pregnancy.

As a sleep aid it is at least as sedating as diphenhydramine and has a longer half-life, which increases both efficacy for occasional use and the likelihood of next-morning hangover. As with all sedating antihistamines, tolerance to the hypnotic effect develops within days, and its anticholinergic profile makes it unsuitable for regular use or for older adults.

02 Mechanism

Central histamine H1 receptor antagonism suppresses histaminergic arousal; substantial muscarinic antagonism accounts for anticholinergic effects.

03 Dosing

Tier	Dose	Route	Notes
Sleep aid	25 mg	Oral	25 mg ~30 min before bed; for short-term occasional use.

04 Effects

Effect	Magnitude	Evidence
Sedation / reduced sleep onset latencyStrongly sedating; shortens time to fall asleep for occasional use.		Clinical
Antiemetic effect (with pyridoxine)Combined with vitamin B6 it reduces nausea and vomiting of pregnancy, a distinct approved use.		Clinical

05 Side effects

Effect	Severity	Frequency	Evidence
Rapid toleranceHypnotic effect fades within several nights of continuous use.	Mild	Nearly universal with nightly use	Clinical
Prolonged next-day sedation (hangover)Long half-life produces marked next-morning drowsiness and impaired alertness.	Moderate	Common	Clinical
Anticholinergic effectsDry mouth, constipation, blurred vision, and urinary retention.	Moderate	Common	Clinical

06 Legal status

Australia

Pharmacy medicine

Available OTC (Restavit). · as of Jan 2026

United States

OTC

Sold over the counter (Unisom SleepTabs). · as of Jan 2026

07 References

Doxylamine succinate as a nighttime sleep aid: efficacy reviewCurr Med Res Opin, 1990s review

American Geriatrics Society Beers Criteria (anticholinergics)J Am Geriatr Soc, 2023 update

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.