Almost everyone all around the world has used Benadryl at some point or another. This medication is commonly used for allergy purposes, and it is typically very safe.

However, the drug can have some severe side effects.

Before consuming Benadryl, it is good to take the time to evaluate the risks and effects of the medication.

Within this guide, you will learn exactly how long Benadryl last and how long it’ll remain in your system.

What Is Benadryl?

First and foremost, it is a good idea to learn the basics of this medication. Although it is more frequently referred to as Benadryl, the medical name is diphenhydramine.

It is an antihistamine and is commonly used for the alleviation of the symptoms of allergic reactions, as well as motion sickness.

Although it is less common, Benadryl can also be used to help treat Parkinson’s disease.

How Long Does Benadryl Stay In Your System?

To understand exactly how long this medication will remain in your system, it is essential to learn about its half-life. 

This medication’s exact half-life can vary depending on several different factors, including metabolism and age.

Below, you will find the average high-life for each age group.

  • Children – 7 hours
  • Adults – 12 hours
  • Elderly – 17 hours

It should be known that the half-life helps to determine how long it’ll take for half of the drug to dissipate from your body.

Therefore, you would need to multiply these figures by two to get your answer.

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These answers will be provided below for your convenience.

  • Children – 14 hours
  • Adults – 24 hours
  • Elderly – 34 hours

On average, it’ll take a day for Benadryl to leave your system completely.

Side Effects

Benadryl is prescribed to treat an allergic reaction since it can block histamine, which is produced by the immune system.

This antihistamine causes many different side effects, which range from mild to moderate and include the following:

  • Vertigo (dizziness)
  • Headache
  • Dry oral and nasal cavities
  • The sensation of needing to urinate frequently
  • Drowsiness
  • Fatigue
  • Dysuria (difficulty urinating)
  • Some users may experience paranoia and anxiety when taking Benadryl over long periods.
  • Drug Interactions

It is crucial never to take Benadryl when you are being prescribed a benzodiazepine (Xanax) and serotonin reuptake inhibitors (Prozac) because it can increase the side effects dramatically.

This can also increase the risks of antihistamine overdose. Be sure to notify your physician if you are currently taking a regimen of these drugs before consuming Benadryl.


Benadryl isn’t necessarily dangerous, but it is a good idea to know exactly how long it’ll last in your system.

This will help to ensure that the medication’s side effects don’t negatively impact you.

With this in mind, you should never consume this drug before you head to work or when you’re going to drive a vehicle. Give yourself 24 hours before partaking in any of these tasks.

David Warren

David Warren is a pharmaceutical specialist that dispenses prescription medication on a daily basis. He received a Bachelor of Science degree in pharmacy from the University of Tennessee in 1991. With over 50 publications on medication-related and pharmacy topics, David has been able to share his experiences and knowledge with others. David with lots of experience and knowledge in medications that are utilized to treat a wide range of medical conditions. Before David dispenses a medication to a patient, he will go over the side effects, dosage recommendation and contraindications.


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    After 24 hours you’d still have 25% left (for an adult). You don’t just double the half life to see when it’s gone, you scientifically illiterate morons.

  2. Avatar
    Bruce Lee Chang

    If you have liver problems do not take any Naproxen, aspirin or worst of all Tylenol, or any form of naproxen. Important to heed If you have any form of Hepatitis. Some Insurance co ask for blood test so not only is it bad for you the screening is very invasive and cutoff levels are below sahmsa levels eg. They are so low they cannot be used for legal or pain mgmt. ie cutoff for opiate is 2000nl or 50ml for sahmsa insurance is ,10-20 so don’t think your getting away with stopping a few days after use blood is only 12 hours but these co( who make it impossible to try to cheat) but worst of all your specialist most common RN. Must ask not only what pain meds your on but ask what over the counter or any Meds your benadryl, and active ingredients, allergy medication you can by over the counter will cause not maybe but definitely will cause false positive. If they don’t ask or tell you this information you WILL fail from false positive and have a strong lawsuit to pursue!

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    I had an adverse reaction to iodine and I was given some benadryl. The hives went away, I got sleepy and confused. The one thing that is bothering me still and it has been over 24 hours, is that I have now having pvcs. I am 57 and confused. One doctor says don’t worry about it. But I am still concerned. Has anyone else had pvcs after taking this drug

  4. Avatar

    I don’t think that’s how half lives work…

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