Doxylamine, sold under the brand name Unisom among others, is an antihistamine medication which is used in the treatment of insomnia and allergies. In combination with pyridoxine (vitamin B6), it is also used to treat morning sickness in pregnant women. Doxylamine is available over-the-counter, and is used in nighttime cold medicines, such as NyQuil, as well as in pain medications containing acetaminophen and codeine, to help with sleep. The medication is taken by mouth. Side effects of doxylamine include dizziness, drowsiness, grogginess, and dry mouth, among others. Doxylamine is an antihistamine—specifically an inverse agonist of the histamine H1 receptor—and to a lesser extent an anticholinergic—specifically an antagonist of the muscarinic acetylcholine receptors M1 through M5. It is a first-generation antihistamine and crosses the blood-brain barrier into the brain, thereby producing centrally mediated sedative and hypnotic effects. Doxylamine was first described in 1948 or 1949. Several of the first-generation antihistamines, including doxylamine, are the most widely used sleep medications in the world. Medical uses
Doxylamine is an antihistamine used to treat sneezing, runny nose, watery eyes, hives, skin rash, itching, and other cold or allergy symptoms. It is also used as a short-term treatment for insomnia. Insomnia
The first-generation sedating antihistamines diphenhydramine, doxepin, doxylamine, and pyrilamine are the most widely used medications in the world for preventing and treating insomnia. As of 2004, doxylamine and diphenhydramine, which are both over-the-counter medications, were the agents most commonly used to treat short-term insomnia.
Available forms
Doxylamine is used medically as doxylamine succinate, the succinate salt of doxylamine, and is available both alone (brand names Decapryn, Doxy-Sleep-Aid, Unisom) and in combination with pyridoxine (a form of vitamin B6) (brand names Bendectin, Bonjesta, Diclegis). Doxylamine is available alone as immediate-release oral tablets containing 25 mg doxylamine succinate. Oral tablets containing 12.5 mg doxylamine succinate as well as oral capsules containing 25 mg doxylamine succinate were also previously available but were discontinued. The combination of doxylamine and pyridoxine is available in the form of extended- and delayed-release oral tablets containing 10 to 20 mg doxylamine succinate and 10 to 20 mg pyridoxine hydrochloride. Doxylamine alone is available over-the-counter, whereas doxylamine in combination with pyridoxine is a prescription-only medication. Doxylamine is also available in over-the-counter nighttime cold medicine products such as NyQuil Cold & Flu (contains acetaminophen, doxylamine succinate 6.25 to 12.5 mg, and dextromethorphan hydrobromide), where it serves as the sedating component. Contraindications
The fetal safety rating of doxylamine is "A" (no evidence of risk). Side effects
Side effects of doxylamine include dizziness, drowsiness, and dry mouth, among others. Doxylamine is a potent anticholinergic and has a side-effect profile common to such drugs, including blurred vision, dry mouth, constipation, muscle incoordination, urinary retention, mental confusion, and delirium.Because of its relatively long elimination half-life (10–12 hours), doxylamine is associated with next-day effects including sedation, drowsiness, grogginess, dry mouth, and tiredness when used as a hypnotic. This may be described as a "hangover effect".