Benadryl is a type of antihistamine that’s available over-the-counter (OTC). It’s most commonly used to relieve allergy symptoms, such as:
- runny nose
The active ingredient in Benadryl is called diphenhydramine. Like any medication, Benadryl has several side effects. Some of the most common are:
It’s also possible that after taking Benadryl some people can feel:
Continue reading to find out why this happens and what to do if it does.
One of the most common side effects of Benadryl is drowsiness. Because of this, some people use Benadryl as a sleep aid.
However, it’s also possible that Benadryl can do the opposite. When a medication has an effect that’s the opposite of what’s expected, it’s called a paradoxical effect.
In some people, taking Benadryl can actually have a stimulant effect, which is called paradoxical excitation. People that experience this after taking Benadryl may report feeling:
Why does this happen?
It’s generally unknown why paradoxical excitation happens in some people and not others.
One theory from a 2008 case report has to do with a type of genetic variation. Three people reporting paradoxical excitability as a response to diphenhydramine had extra copies of a specific gene.
This gene encodes instructions to make an enzyme called CYP2D6. CYP2D6 is important for breaking down (metabolizing) certain types of medications, such as Benadryl. Having extra CYP2D6 can make Benadryl metabolism much faster.
The researchers above hypothesized that it’s possible that in these people, Benadryl could be quickly broken down into substances that lead to excitability, rather than sedation. However, more research is needed to confirm this.
How common is it?
There aren’t currently any estimates of how common paradoxical excitation is in people that take Benadryl.
If the theory about fast metabolism is correct, a significant number of people in the United States could be impacted. The 2008 case report discussed above estimated that 1% to 2% of people in the United States have the genetic variation.
Additionally, it appears like paradoxical excitation is more common in children. You’ll actually see this effect listed on the labels of Benadryl products.
Taking Benadryl can slow, or depress, the functions of your central nervous system (CNS).
This is what can lead to some common side effects of Benadryl, such as drowsiness or dizziness. It’s also why some people may use Benadryl to help them to sleep or to feel less anxious.
Now that we’ve discussed how Benadryl may be connected to feelings of excitability or anxiousness, you may be wondering if Benadryl has any other similar side effects. Let’s look into this now.
It’s possible for a person to become dependent on Benadryl. This can happen if it’s used frequently over a period of time, such as if you use Benadryl every day for 2 weeks or longer, according to the National Health Service.
When someone becomes dependent on a substance, they may also experience withdrawal symptoms when they stop using it. These can include:
It’s important to always take Benadryl as directed by the product label or by your doctor.
Because continuous use of Benadryl can lead to dependence, call a doctor if you find that you’re taking Benadryl frequently for conditions like allergies or sleep. They can recommend alternative medications that you can try instead.
Benadryl and dementia
It’s possible that long-term use of Benadryl could increase the risk of developing dementia, according to a
The study found that a higher cumulative use of anticholinergic drugs was associated with an increased risk of dementia in this group. Examples of some types of anticholinergic drugs include:
- first-generation antihistamines, like Benadryl
- tricyclic antidepressants (TCAs)
- certain medications used to treat an overactive bladder
- medications used to treat Parkinson’s disease symptoms
If you’re concerned about Benadryl and dementia, be sure to only take Benadryl for a short amount of time. You may also consider asking a doctor about alternative medications that may help treat your symptoms.
Benadryl can be found in several forms, including:
You can find Benadryl products available OTC at grocery stores and pharmacies.
Benadryl tablets or capsules
According to the National Institutes of Health, Benadryl tablets or capsules contain 25 milligrams of diphenhydramine, the active ingredient. The recommended dosage of Benadryl is:
- Ages 12 and up: a total of 1 to 2 tablets every 4 to 6 hours
- Ages 6 to 12: a tablet every 4 to 6 hours
- Under age 6: do not take
There are also liquid formulations of Benadryl that can be used for children. When measuring liquid Benadryl, it’s important to use the little cup that comes with the medication. Don’t measure doses using a kitchen spoon.
According to the National Institutes of Health, for this type of Benadryl, the recommended dosage is:
- Ages 6 to 12: a total of 1 to 2 teaspoons (5 to 10 milliliters) every 4 to 6 hours
- Ages 4 to 6: only use under the direction of your child’s pediatrician
- Under age 4: do not take
Tips for taking Benadryl safely
It’s also important to follow the guidelines below to ensure that you take Benadryl safely and lower your risk of side effects:
- Don’t take too much in a day. Avoid taking more than 6 doses of Benadryl in one 24-hour period.
- Use only as needed. Because Benadryl can cause long-term side effects, be sure to only take it for a short amount of time.
- Avoid other sedatives. Because Benadryl often has a sedating effect, avoid taking it with other sedative medications, sleep aids, or alcohol.
- Be careful with activities. Since Benadryl can make you drowsy, avoid driving or operating heavy machinery after taking it.
- Speak with your doctor if you:
- take sedative medications or a type of antidepressant called a monoamine oxidase inhibitor (MAOI)
- have lung conditions (asthma, chronic bronchitis, or emphysema)
- have glaucoma, stomach ulcers, seizures, or trouble urinating due to an enlarged prostate
- are pregnant or breastfeeding
- had a previous allergic reaction to Benadryl
Generally speaking, you don’t need to call a doctor if you’ve taken Benadryl and are experiencing feelings of:
Feelings of paradoxical excitement typically only last for the length of time that Benadryl is in your system. This can be about 4 to 6 hours.
Instead, you can try:
- taking deep breaths or counting to 10 slowly may help you to feel calmer
- avoiding other stimulants like caffeine or nicotine
- getting exercise, which help to lift your mood
- trying a relaxing activity like yoga or meditation
Speak with a doctor if you would like recommendations for alternative medications that are less likely to have these side effects.
Taking too much Benadryl can lead to an overdose. If you or someone else has taken Benadryl and has any of the symptoms below, go to the emergency room or call 911.
- blurry vision
- rapid or irregular heart rate
- nausea or vomiting
- dilated pupils
- trouble emptying your bladder (urinary retention)
- confusion or disorientation
- low blood pressure (hypotension)
One of the most common side effects of Benadryl is drowsiness. However, some people may find that taking Benadryl causes them to feel:
It’s unknown what exactly causes the above side effects to happen. If you take Benadryl and experience anxiety or agitation, you can do a few things to help ease these feelings until the medication wears off. Some examples include taking deep breaths or doing a relaxing activity.