One of the most common side effects with Benadryl is drowsiness, but in some people it can have the opposite effect, known as paradoxical excitation. Instead of feeling sleepy,
you may experience excitation, agitation or insomnia (trouble sleeping), which might make your anxiety symptoms feel worse. This may be more common in young children.
Some of the common central nervous system (CNS) side effects that may be related to paradoxical excitation with Benadryl include:
- Agitation
- Anxiety
- Excitation
- Insomnia (trouble sleeping)
- Irritability
- Restlessness
- Tremors (the jitters)
If you notice these symptoms after taking Benadryl, contact your doctor. They might suggest you or your child stop taking the medicine and recommend an alternative, if needed. The side effects should clear up in about a day once the medication is stopped.
If Benadryl (generic name: diphenhydramine) has been prescribed or recommended by your healthcare provider, contact them first before you stop treatment.
You should not use Benadryl to make a child sleepy or give this medication to a child younger than 2 years of age. Always ask your doctor before giving any cough or cold medicine to a child. Death can occur from the misuse of cough and cold over-the-counter (OTC) medicines in very young children.
Why does Benadryl cause paradoxical excitation?
It’s not known exactly why paradoxical excitation with Benadryl occurs. It is thought that it may have to do with the way the drug is metabolized (broken down) in the body for excretion, as described in one small case report.
- Benadryl is metabolized in the liver by an enzyme known as CYP2D6. It also appears to inhibit (or blocks) the use of this enzyme.
- Some people have extra copies of the 2D6 gene and are called "ultrarapid metabolizers". These people can quickly break down CYP2D6 substrates like diphenhydramine, the active ingredient in Benadryl.
- The researchers suggested that in people who are CYP2D6 ultrarapid metabolizers, a compound may be created that leads to excitation instead of the typical drowsiness, but they also say more research is needed to explore this idea.
Does anxiety occur if I take too much Benadryl?
Paradoxical excitation can occur even with normal doses of Benadryl, but taking too much Benadryl can be dangerous or even deadly. In children, an antihistamine overdose may cause hallucinations, convulsions (seizures), or death.
Symptoms of an overdose may include:
- Vomiting
- Confusion
- Extreme drowsiness
- Ringing in the ears
- Dry mouth
- Dry eyes
- Dilated pupils
- Limited urination
- Flushing
- Rapid heartbeat
- Seizures
- Tremors or shaking
- Agitation
- Hallucinations
If you or your child has taken an overdose of diphenhydramine (Benadryl), call right away for emergency medical help (dial 911 in the US) or contact the Poison Control Helpline at 1-800-222-1222.
This is not all the information you need to know about Benadryl (diphenhydramine) for safe and effective use and does not take the place of your doctor’s directions. Review the full product information or Drug Facts Label discuss this information and any questions you have with your doctor or other health care provider.