Chronic diphenhydramine abuse and withdrawal

Diphenhydramine (DPH) acts on peripheral and central histamine H1 receptors, causing reduction of allergic symptoms and sedation, respectively.1 It is also a potent competitive antagonist of muscarinic acetylcholine receptors and can cause sinus tachycardia, xerostomia, mydriasis, blurred vision, ileus, urinary retention, CNS depression, agitation, hyperactivity, or psychosis. Given multiple potential mechanisms of action and its use for a variety of conditions, cases of medication misuse and abuse have been reported,2–5 primarily due to behavioral effects such as elevated mood, increased energy levels, and mild euphoria.6