HealthTap Online Primary Care Doctors Accepting New Patients
Book a video visit
HealthTap
Telehealth
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
Dr. John Chiu answered

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

3.3k views

Thank

Related Questions

A member asked:

Took benadryl yesterday afternoon to sleep, today woke up with a brain vibration, dont remember if it was my whole body. No muscle problems. Was cold

A doctor has provided 1 answer

A member asked:

What causes paradoxical reactions to benadryl (diphenhydramine). What mechanism ocurrs in the brain that makes the person stimulated rather than drowsy?

2 doctors weighed in across 2 answers

A member asked:

Hello. If I take Benadryl in the morning and Quetiapine 50mg at night would they still interact? If I take them separately. I take 50mg of Quetiapine for sleep and I need the Benadryl for my chronic cystitis, probably IC. They say Benadryl will help?

A doctor has provided 1 answer

A member asked:

Tried benadryl, (diphenhydramine) zyrtec & allegra. I get extremely dizzy with brain fog from all of them. Is there anything else to try for chronic idiopathic hives?

2 doctors weighed in across 2 answers

A member asked:

Dr thinks I have shingles(left back under bra line & on left breast but not positive! He gave me keflex bc infected and Benadryl (diphenhydramine).Will it go to brain?

A doctor has provided 1 answer

Sponsored Content
HealthTap Medical Group does not endorse products or services. Sponsored content revenues support our mission to make health information free and accessible to all.Learn more

People also searched for:

Best sleep medication for long term use? Cant shut mind off at night. Benadryl makes me groggy. Klonopin causes brain atrophy(?) Melatonin dont work
600mg of Benadryl (diphenhydramine) GREATLY improves my quality of life. Could something be restricting bloodflow in my brain? Is there a safe alternative?
Do Benadryl (diphenhydramine) and Adderall interact with each other?
I have a mild allergy to tuna. But it is slowly getting worse. I can feel my brain itching. Will Benadryl help with that?
I took 5mg of Valium 6 hours ago... Is it safe to take 30 ML of diphenhydramine now to fall asleep? Or will the two interact?

Telemedicine

Primary Care
Manage Your Conditions
Women's Health
Children's Health
Men's Health
Senior Health
Wellness, Prevention & Lifestyle
Sexual Health
Mental & Behavioral Health
Travel Medicine
Urgent Care
Ask your question
Didn't find what you're looking for?

90,000 U.S. doctors in 147 specialties are here to answer your questions or offer you advice, prescriptions, and more.

Ask your question

More of what we treat

Allergies
Antibiotics
Asthma
High Blood Pressure
Prescriptions
Type 2 Diabetes
Content on HealthTap (including answers) should not be used for medical advice, diagnosis, or treatment, and interactions on HealthTap do not create a doctor-patient relationship. Never disregard or delay professional medical advice in person because of anything on HealthTap. Call your doctor or 911 if you think you may have a medical emergency.
HealthTap
HIPAA logo
HIPAASecure
Soc 2 Type 2 logo
SOC 2 Type 2Certified
JCAHO Accredited
JCAHOAccredited
Member App

Download HealthTap

Video visit and message your doctor

Member App QR Code
Play Store Member LinkApp Store Member Link

Questions?

+1 (888) 828-0841support@healthtap.com
LinkedInTwitter
HomeTermsPrivacyCookiesDMCAHealth TopicsDoctors DirectoryDoctor Q&A by Specialty
Copyright 2026 HealthTap, Inc.