Can Benadryl Make You Hyper?
In our latest question and answer, the pharmacist discusses how and why Benadryl (diphenhydramine) can cause paradoxical stimulation/excitation in some individuals.
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?
Oct 27, 2022- Benadryl can cause the opposite of its intended sedating effect in some people, making them feel "hyper" or anxious, especially in children and adolescents.
- Symptoms of this paradoxical reaction include restlessness, agitation, nervousness, and insomnia, but these effects typically last only as long as the medication's duration of action, which is about four to six hours.
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 Spasms
- 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
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References & sources
Glossary — Terms in This Answer
- Antihistamine
- A medication that blocks histamine, a chemical in the body that causes allergy symptoms like itching and swelling.
- Paradoxical excitation
- An unexpected reaction where a medication produces the opposite effect than intended, such as a sleep aid causing wakefulness instead.
- CNS stimulation
- Increased activity in the brain and nervous system that can cause restlessness, agitation, or anxiety.
- Metabolites
- Substances created when the body breaks down a drug into different chemical forms.
- Half-life
- The amount of time it takes for the body to eliminate half of a drug's dose.
- Ultra-rapid metabolizers
- People whose bodies break down medications much faster than average due to genetic variations.
- CYP2D6
- An enzyme in the body responsible for breaking down certain medications, including Benadryl.
- Metabolism
- The process by which the body breaks down a drug into other substances so it can be eliminated.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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