Diphenhydramine

Diphenhydramine is a sedating, antiallergic, and anticholinergic agent belonging to the first-generation antihistamines.‍​‍‍‍​‍‍‍‍‍‍‍‍​‍ It is used for the treatment of sleep disorders, allergic conditions, prevention of motion sickness, and common cold symptoms, among other indications. Its effects are based on inverse agonism at histamine receptors and antagonism at muscarinic acetylcholine receptors. When used as a sleep aid, the medication is taken 15 to 30 minutes before bedtime. The most common possible adverse effects include drowsiness, somnolence, and dizziness. Diphenhydramine may prolong the QT interval. Diphenhydramine (ATC D04AA32, ATC R06AA02) has antihistaminic, antiallergic, sedating, antiemetic, local anesthetic, spasmolytic, and anticholinergic properties. Its effects are based on inverse agonism at peripheral and central histamine receptors and antagonism at muscarinic acetylcholine receptors. Additionally, diphenhydramine blocks sodium channels, which produces local anesthesia. The half-life is approximately 5 hours. Diphenhydramine also inhibits the reuptake of serotonin. The antidepressant fluoxetine was derived from it. Mechanism of action of antihistamines, click to enlarge. Illustration © PharmaWiki