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A 44-year-old member asked:

How much time after you take cough medicine do you feel the sleepy side effects?

1 doctor answer1 doctor weighed in
Dr. Rajnish Jaiswal
Emergency Medicine 24 years experience
About 1-3 hrs: Most night time cold meds contain an antihistamine that helps you fall asleep. Diphenhydramine and Doxylamine are the common drugs used and their onset of action is from 1-3 hours and 2-3 hrs respectively. Most other antihistamines would have a similar onset of action.

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Last updated Oct 29, 2015

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