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Dr. Andrew Rynne
MD
Dr. Andrew Rynne

Family Physician

Exp 50 years

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How Long Does Diphenhydramine Stay In The System?

I am scheduled to take a drug test for employment within the next 48 hours. I have been taking Tylenol PM and am worried that it may produce a false positive. How long does Diphenhydramine normally stay in your system? I took 50 mg at 3:00 AM on Monday. Should it be out of my system by Wednesday afternoon? Thanks for your help.
Fri, 30 Mar 2018
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General & Family Physician,  's  Response
Hello,

It will take about 36 to 40 hours for Diphenhydramine drug to go out of your system.

The plasma elimination half-life (time taken for the 50% removal of the drug from the body) following single dose of Diphenhydramine is about 9 hours (range: 7 to 12 hours).

So, for a 50 mg dose it will take about 36 to 40 hours to eliminate Diphenhydramine from your system.

Many over the counter drugs like Tylenol PM which is a combination of Acetaminophen & Diphenhydramine can cause a false positive test.

Hope I have answered your query. Let me know if I can assist you further.

Regards,
Dr. Mohammed Taher Ali
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How Long Does Diphenhydramine Stay In The System?

Hello, It will take about 36 to 40 hours for Diphenhydramine drug to go out of your system. The plasma elimination half-life (time taken for the 50% removal of the drug from the body) following single dose of Diphenhydramine is about 9 hours (range: 7 to 12 hours). So, for a 50 mg dose it will take about 36 to 40 hours to eliminate Diphenhydramine from your system. Many over the counter drugs like Tylenol PM which is a combination of Acetaminophen & Diphenhydramine can cause a false positive test. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Mohammed Taher Ali