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A 18-year-old male asked:

How long would it take for 100mg of diphenhydramine hydrochloride to sedate a 55kg male?

2 doctor answers3 doctors weighed in
Dr. Bac Nguyen
Family Medicine 23 years experience
Rapid absorption: Commonly known as benadryl, (diphenhydramine) and otc med, is very well absorbed and can start having an effect as early as 15 minutes. I would say that by 30 min, you would likely feel the sedative effect, if it works on you. It will last about 4-6 hours. Likely all med, use the smallest effective dose for shortest time possible. Consult doc. Good luck.
Dr. John Chiu
Allergy and Immunology 57 years experience
If it works: It should start working between 60-90 minutes based on my own experience but the sedating effects vary from person to person with some not experiencing any significant drowsiness at all . Do note that the sedating effect usually decreases with daily use.

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Last updated May 12, 2017

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