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What is the half life of Benadryl?

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Posted on Wed, 11 Mar 2015
Question: How long for a single dose of benadryl to leave your system. I took it 4hrs ago & am having a bad reaction
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Answered by Dr. Noble Zachariah (31 minutes later)
Brief Answer:
Usually 6 to 8 hours. Go to ER if it's bad reacti

Detailed Answer:
Hello,
Welcome to HCM and thanks for your query. The plasma half-life is 1 to 4 hours, so the drug should be out of the system in about 8 hours.
So if you are having a bad reaction, it is better to go to the ER if it is a dangerous reaction.
Take care,
Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar
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Follow up: Dr. Noble Zachariah (9 hours later)
It has been 12 hours and Im still throwing up is it still in me?
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Answered by Dr. Noble Zachariah (1 hour later)
Brief Answer:
Should consider another cause if not well

Detailed Answer:
Sorry for the delay in replying as we live in two different time zones.
If you are not free of symptoms by now, there must be another cause than Benadryl.
Please see a doctor and sort things out.
I am available for answering further queries if any.
Take care
Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar
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Answered by
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Dr. Noble Zachariah

Internal Medicine Specialist

Practicing since :1974

Answered : 2318 Questions

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What is the half life of Benadryl?

Brief Answer: Usually 6 to 8 hours. Go to ER if it's bad reacti Detailed Answer: Hello, Welcome to HCM and thanks for your query. The plasma half-life is 1 to 4 hours, so the drug should be out of the system in about 8 hours. So if you are having a bad reaction, it is better to go to the ER if it is a dangerous reaction. Take care,