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A member asked:
How long does benadryl (diphenhydramine) allergy med stay in your system?
A doctor has provided 1 answer
7-18 hr, effectively: That's with a normal dose. The half-life (time it takes 1/2 the med to leave your body) is 3.4 to 9.2 hrs. Double that time and 75% of it has left your system at which point it's generally not helping anymore. Triple it and 87.5% is gone, etc. If you take twice the normal dose you could still have a significant amount after more than 24 hours.
Answered 8/4/2017
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