How Does Benadryl Affect Your Kidneys, Liver, and Heart?

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 drugs 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 dose. 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 larger 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 most 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.

Benadryl also has an anticholinergic effect on the body. This means it blocks another chemical in the body called acetylcholine. This helps dry up a runny nose and watery eyes. But it can also cause side effects, such as constipation 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.

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If you’re 65 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 your healthcare provider 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. Benadyl’s anticholinergic properties can affect your heart and other organs, such as your brain. 

Even at recommended doses, Benadryl can cause sleepiness, confusion, and dizziness. At higher than recommended doses, it can cause seizures. 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.

Benadryl can cause low blood pressure and/or a fast heartbeat in some people. And if you take too much Benadryl, it can cause an irregular heartbeat (arrhythmia) that could be fatal if left untreated. If you have a history of heart disease, it’s best to talk to your healthcare provider before taking Benadryl.

Is it safe to take Benadryl every day?

Benadryl isn’t something you should take every day without a healthcare provider’s approval. It is 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?

It’s best to take the lowest effective Benadryl dose for your symptoms to lessen the chance of side effects. For adults and children ages 12 years and older, it’s not recommended to take more than 50 mg per dose or more than 6 doses of Benadryl in a 24-hour period. 

For children under the age of 12, the Benadryl dose is based on their age and weight. Follow the package instructions or talk to your healthcare provider 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 your healthcare provider 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 seek emergency care. 

Who shouldn’t take Benadryl?

In some cases, Benadryl is not recommended without a healthcare provider’s OK. This includes children under the age of 5 and adults over the age of 65. You should also check with your healthcare provider before taking Benadryl if you have:

• Asthma or other lung-related conditions

• High pressure in your eyes (glaucoma)

• Heart disease

• Trouble urinating

Why trust our experts?

Written by:

Nicole E. Cieri-Hutcherson, PharmD, BCPS, NCMP

Nicole E. Cieri-Hutcherson, PharmD, BCPS, NCMP, has over a decade of experience as a pharmacist, professor, and researcher. She was a full-time clinical professor in the pharmacy practice department at D’Youville School of Pharmacy before subsequently joining the faculty of the pharmacy practice department at the University at Buffalo School of Pharmacy and Pharmaceutical Sciences.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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