Can Benadryl Make You Hyper?
In our latest question and answer, the pharmacist discusses how and why Benadryl (diphenhydramine) can cause paradoxical stimulation/excitiation in some individuals.
Question
I am a 45-year-old female that recently started taking 50 to 100 mg of Benadryl off and on for 2 weeks to calm a cough at night. During this time, I've had fast heart rate, eye focus problems, weakness, and breathing problems at night. I was still going to sleep until my last dose when I awoke to panic and a heart rate of 130. I stayed up all night and still have anxiety the next day and evening. Can Benadryl do this? Make you hyper and anxious?
Answered by Dr. Brian Staiger, PharmD
Medical Content Reviewed By HelloPharmacist
Staff
Last updated Apr 28, 2025
Key points
- While Benadryl most commonly causes sedation and drowsiness, some individuals have an opposite reaction and can feel stimulated or hyper.
- This type of reaction is more common in children than adults but has been reported in all ages.
- The exact mechanism behind Bendaryl causing excitation in some individuals is not known, but one theory suggests this occurs to due a difference in how some metabolize the drug.
Answer
Benadryl (diphenhydramine) is a commonly used antihistamine for the treatment and prevention of allergies. In addition, due to its sedating properties, it is used before bedtime to help combat insomnia and induce drowsiness.
Somewhat surprisingly, Benadryl can have the opposite effect in some individuals and cause CNS (central nervous system) stimulation, even at recommended dosages. This is sometimes known as paradoxical excitation.
Some describe this reaction as making them feel "hyper" or anxious Studies indicate that this occurs most commonly in children and adolescents but has been reported in adults as well.
Benadryl Causes CNS Stimulation In Some Individuals
Symptoms of paradoxical CNS stimulation include:
- Restlessness
- Agitation
- Muscle Spams
- Insomnia
- Nervousness
- Irritability
- Seizures (rare)
The incidence of CNS excitation with Benadryl use isn't known and the mechanism behind it isn't well understood either.
One possible theory involves individuals who have a genetic variation that causes multiple copies of a metabolizing enzyme known as CYP2D6. These individuals are known as "ultra-rapid metabolizers". It is thought that Benadryl may be quickly converted to a compound (due to extensive metabolism) that causes excitation.
How Long Can These Side Effects Last?
Whatever the cause, CNS stimulation doesn't tend to last longer than the usual duration of action of Benadryl, about four to six hours. Occasionally, the effects may last slightly longer due to longer-lasting metabolites.
Studies indicate the half-life (i.e., the time it takes for 50% of the drug to be metabolized) of Benadryl and associated metabolites is 2-8 hours and is completely eliminated within 24-48 hours. Therefore, your side effects shouldn't continue for more than one or two days.
Final Words
Thanks for reaching out! Please contact us again anytime.
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Dr. Brian Staiger, PharmD
- 10286 views
About the Pharmacist
Dr. Brian Staiger, PharmD
Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at [email protected]! You can also connect with Dr. Brian Staiger on LinkedIn.
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