Doxylamine succinate is an over-the-counter first-generation antihistamine that is commonly used as a short-term treatment for insomnia. Its sedative effects are well-documented and result from its ability to cross the blood-brain barrier and block central histamine H1 receptors, which play a role in wakefulness. Clinical studies have demonstrated that doxylamine can decrease sleep latency (the time it takes to fall asleep) and increase total sleep time compared to placebo in adults with transient insomnia. The U.S. Food and Drug Administration (FDA) recognizes doxylamine as a sleep aid, and it is included in several OTC sleep medications.

However, the quality and quantity of scientific evidence supporting doxylamine's efficacy for insomnia is moderate. Most studies suggest only modest benefits, and there is limited data on long-term use or effectiveness in chronic insomnia. Additionally, like other first-generation antihistamines, doxylamine may cause side effects such as next-day drowsiness, dry mouth, urinary retention, and confusion, particularly in older adults. For these reasons, clinical guidelines often recommend non-pharmacological approaches as first-line therapy for insomnia, reserving short-term use of medications like doxylamine for selected cases.

In summary, doxylamine succinate's use for insomnia is scientifically validated for short-term use, with evidence supporting its sedative effects, though benefits are modest and safety concerns limit its routine use.