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A member asked:
If benadryl's plasma clearance is about 9 hours x 5, how long would it remain active to affect the brain and interact with other medications?
A doctor has provided 1 answer
Less than 12 hrs: It may take a long time for a drug to completely clear from the body, the biochemical effect occurs only with a certain blood level. I have yet seen anyone getting drowsy from Benadryl (diphenhydramine) for more than 12 hours. It is the drug level that matters.
Answered 1/24/2015
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