What is the adult dose of diphenhydramine?

• A. 5-10 mg PO
• B. 25-50 mg PO
• C. 100-200 mg PO
• D. 75-125 mg PO

Answer: (B)

Diphenhydramine is an antihistamine used to relieve allergic symptoms, and the typical adult oral dose is 25-50 mg per dose, given every 4-6 hours as needed. This range provides effective symptom relief while balancing the risk of sedation and anticholinergic effects. Smaller doses like 5-10 mg are usually not enough for a noticeable antihistamine effect in adults, whereas much larger single doses (such as 75-125 mg or 100-200 mg) raise the likelihood of excessive drowsiness, confusion, and other adverse effects. In practice, many guidelines also note a daily maximum around 400 mg, so dosing should avoid exceeding that limit.