How should i treat diphenhydramine overdose?

Go to ER: The national poison control center (1-800-222-1222) recovery is likely if the patient survives the first 24 hours. Normally this is treated with hydration and monitoring, occassionally treated with activated charcoal. Few patients actually die from an antihistamine overdose, unless there have been serious heart rhythm disturbances or breathing problems.

Call 911: You should not treat it - get emergency medical care. Treatment for Diphenhydramine O/D may include: administration of activated charcoal, intravenous fluids, intubation, Sodium Bicarbonate (Cardiac), Physostigmine, & benzodiazpines or barbituates for seizures. REF: https://overdoseinfo.com/diphenhydramine-overdose/