Key takeaways:
Benadryl doesn’t normally harm the liver, kidneys, or heart at recommended doses.
At higher than recommended doses, Benadryl could harm the kidneys or liver. This is also true if you combine Benadryl with certain medications.
Too much Benadryl can cause a life-threatening irregular heartbeat. It’s best to talk with a healthcare professional before taking Benadryl if you have heart disease.
Benadryl isn’t recommended for older adults due to higher risk of side effects.
Save on related medications
Benadryl (diphenhydramine) is a medication that’s often used for different types of allergic reactions. It was FDA approved in 1946 and is now available both by prescription and over the counter (OTC). It’s also in the top 200 medications prescribed each year, reaching more than 2.5 million prescriptions in 2020.
If you’re taking Benadryl, you may wonder about its possible side effects. And more specifically, you may want to know if it’s bad for your kidneys or liver. For most people, Benadryl is safe and effective when taken at the recommended daily dosage. But let’s take a closer look at what you need to know about Benadryl and its effect on your body.
How does Benadryl affect the body?
Benadryl belongs to a class of medications known as antihistamines. Histamine is a chemical the body releases to help fight off intruders, such as pollen or mold. It causes common allergy symptoms, such as watery eyes, runny nose, and sneezing. Benadryl blocks the action of histamine, which improves these symptoms. But it can also cause significant drowsiness, which is why diphenhydramine is often found in many OTC sleep medications, too.
Search and compare options
Benadryl also has an anticholinergic effect on the body. This means it blocks another chemical in the body called acetylcholine. Acetylcholine plays a part in muscle contraction, blood pressure, and secretions. So Benadryl can help dry up a runny nose and watery eyes. But it can also cause side effects, such as constipation, dry mouth, and trouble peeing.
Can Benadryl harm your kidneys or liver?
Not usually. Benadryl isn’t known to cause liver or kidney damage in most cases. But there may be certain times when the risk is higher.
Kidney damage
In rare cases, Benadryl has been linked to kidney damage, which is usually reversible. There are two possible causes of kidney injury from Benadryl:
Anticholinergic effect: As mentioned, one side effect of anticholinergic medications is difficulty peeing. Medications like Benadryl can make you hold onto your urine longer than normal (urinary retention). So urine builds up in your bladder. This can cause pressure on your kidneys and lead to kidney damage.
Muscle damage: Benadryl may also damage your muscles (rhabdomyolysis). This kind of muscle damage can lead to kidney damage in some people. This isn’t a common side effect of Benadryl, and is more likely associated with severe overdoses.
If you’re 60 years or older, kidney damage from Benadryl may be more common. In fact, Benadryl is considered a high-risk medication for this age group and isn’t recommended. But if kidney damage does occur, it will resolve in most cases after appropriate medical care.
Symptoms of kidney damage from Benadryl include difficulty peeing, dark-colored urine, and feeling dizzy or confused. If you notice these symptoms while taking Benadryl, contact a healthcare professional right away.
Liver damage
Benadryl hasn’t been linked to liver damage or changes to liver enzymes. This is likely because it’s usually only taken for a short period of time. And its effects don’t last very long in the body.
Keep in mind that many OTC products contain Benadryl in combination with other medications — such as acetaminophen (Tylenol). And too much acetaminophen can cause liver damage. So it’s best to always follow the package instructions for any medication containing Benadryl or diphenhydramine to avoid harm.
Does Benadryl affect your heart or other organs?
Yes. Benadryl’s anticholinergic properties can affect your heart and other organs, such as your brain.
Even at recommended dosages, Benadryl can cause side effects like:
Sleepiness
Confusion
Dizziness
Dry mouth
Constipation
Benadryl side effects: Learn about common side effects from Benadryl (diphenhydramine), plus tips on how to manage them.
Countdown to symptom relief: How long does it take Benadryl to work? See how pharmacists answer this and other frequently asked questions about Benadryl.
Benadryl dosage: Find out how much is too much for both kids and adults.
These symptoms are of particular concern for older adults or if you’re pregnant. But anyone taking Benadryl should be aware of them. Use caution when driving or participating in activities that require your full attention while you’re taking it. You may also consider only taking Benadryl at night, to avoid these issues during the day.
At higher than recommended dosages, Benadryl can cause:
Seizures
Fast heartbeat
Irregular heartbeat (arrhythmia) that could be fatal if left untreated
If you have a history of heart disease, it’s best to talk with a healthcare professional before taking Benadryl.
Long-term effects of Benadryl
Long-term use of Benadryl increases the risk and severity of side effects. But there hasn’t been a lot of research into the effects of chronic Benadryl use.
That said, there have been reports of negative effects from taking Benadryl for a long time. They include increased aggression and agitation in people with major depressive disorder. Some people have become dependent on Benadryl, leading to withdrawal symptoms when they stop taking it.
Is it safe to take Benadryl every day?
Benadryl isn’t something you should take every day without the approval of a healthcare professional. It’s usually only taken as needed for symptoms as they come and go. If you’ve been instructed to take Benadryl on a daily basis, be sure to follow the recommended dosage. Taking more Benadryl than you should is more likely to cause serious side effects.
How much Benadryl is too much?
Taking the lowest effective Benadryl dose for your symptoms can help lessen the chance of side effects.
Adults and children ages 12 years and older can take 25 mg to 50 mg per dose every 4 to 6 hours as needed. Don’t take more than 6 doses (300 mg) of Benadryl in a 24-hour period.
For children under the age of 12 years, Benadryl dosage is based on their age and weight. It’s often much less than what is safe for adults. Follow the package instructions or talk with your healthcare team about how much Benadryl is safe for them to take.
Keep in mind that diphenhydramine, the active ingredient in Benadryl, is found in several different types of medications. Cough and cold medications, sleep medications, and allergy medications can all contain it. So be sure to read the ingredients list for everything you take to make sure you aren’t taking more Benadryl than you realize.
Higher doses than recommended can have dangerous side effects. If you or someone you know has taken too much Benadryl, it’s best to contact a healthcare professional or call Poison Control at 1-800-222-1222. But if you have severe side effects, such as confusion or altered mental status, call 911 or get emergency care.
Who shouldn’t take Benadryl?
In some cases, Benadryl is not recommended without a healthcare professional’s OK. This includes children under the age of 5 years, people who are nursing, and adults over the age of 60 years. You should also check with a healthcare professional before taking Benadryl if you have:
Asthma or other lung-related conditions
High pressure in your eyes (glaucoma)
Heart disease
Trouble urinating
Frequently asked questions
Other OTC options for sleep include melatonin and products with doxylamine (Unisom). Similar to Benadryl, doxylamine is an antihistamine, so it has similar side effects. Melatonin can also cause dizziness and headache. Keep in mind these sleep aids aren’t meant to be used long term. If you have trouble sleeping for more than a few days, be sure to speak with a healthcare professional.
In terms of antihistamine use for allergy symptoms, second- and third-generation antihistamines are safe for long-term use. Examples include cetirizine (Zyrtec) and fexofenadine (Allegra). These medications don’t have anticholinergic effects like Benadryl. And they’re less likely to make you drowsy. Be sure to speak with a healthcare professional if you need antihistamines for more than one allergy season.
Research suggests a link between long-term use of some anticholinergic medications and dementia. But there isn’t good evidence that Benadryl can cause dementia. It’s still best for older adults to avoid Benadryl due to its side effects, like urinary retention and dizziness.
Other OTC options for sleep include melatonin and products with doxylamine (Unisom). Similar to Benadryl, doxylamine is an antihistamine, so it has similar side effects. Melatonin can also cause dizziness and headache. Keep in mind these sleep aids aren’t meant to be used long term. If you have trouble sleeping for more than a few days, be sure to speak with a healthcare professional.
In terms of antihistamine use for allergy symptoms, second- and third-generation antihistamines are safe for long-term use. Examples include cetirizine (Zyrtec) and fexofenadine (Allegra). These medications don’t have anticholinergic effects like Benadryl. And they’re less likely to make you drowsy. Be sure to speak with a healthcare professional if you need antihistamines for more than one allergy season.
Research suggests a link between long-term use of some anticholinergic medications and dementia. But there isn’t good evidence that Benadryl can cause dementia. It’s still best for older adults to avoid Benadryl due to its side effects, like urinary retention and dizziness.
The bottom line
For most people, Benadyl — at recommended dosages — doesn’t have a negative effect on the heart, liver, or kidneys. But if you take more Benadryl than recommended, there could be harmful effects. Mental changes and seizures can occur. In the most severe cases, too much Benadryl can lead to life-threatening heart arrhythmias or kidney damage.
For people ages 60 years and over, there’s a higher risk for confusion, falls, and kidney damage when taking Benadryl. So it’s best to avoid taking it if you’re in this age group. Your primary care provider or pharmacist can help you find a safer alternative to Benadryl.
Why trust our experts?
References
Abraham, O., et al. (2017). Over-the-counter medications containing diphenhydramine and doxylamine used by older adults to improve sleep. International Journal of Clinical Pharmacy.
Andersen, C. L., et al. (2021). Cardiac arrest following the administration of intravenous diphenhydramine for sedation to an infant with congenital heart disease. The Journal of Pediatric Pharmacology and Therapeutics.
Ariza-Salamanc, D. F., et al. (2025). Expert consensus on the use of diphenhydramine for short-term insomnia: Efficacy, safety, and clinical applications. Journal of Clinical Medicine.
ClinCalc.com. (n.d.). The top 200 drugs of 2023.
Contract Pharmacy Services-PA. (2010). Diphenhydramine hydrochloride- diphenhydramine hydrochloride capsule [package insert].
Huynh, D. A., et al. (2023). Diphenhydramine toxicity. StatPearls.
LiverTox. (2017). Diphenhydramine.
Pham, A. Q., et al. (2013). Diphenhydramine and acute kidney injury. P&T.
Ramakrishna, K. N., et al. (2019). Massively elevated creatine kinase levels in antihistamine-induced rhabdomyolysis. Proceedings (Baylor University. Medical Center).
Schifano, F., et al. (2021). Focus on over-the-counter drugs' misuse: A systematic review on antihistamines, cough medicines, and decongestants. Frontiers in Psychiatry.
