Question: how long does diphenhydramine hcl 25 mg last?
Answer: Benadryl is quickly absorbed after oral administration and peak effects are reached within one hour. The effects of diphenhydramine last from four to six hours. Benadryl in the injectable form has a rapid onset of action. When used as a night-time sleeping aid, the usual dosage of Benadryl is 50mg at bedtime.