How Long Does Benadryl Stay In Your System?
In our latest question and answer, the pharmacist discusses how long Benadryl will last in your system.
Hi, My 98-year-old mother was taking 25 mg of diphenhydramine at night for sleep. We have stopped it, but how long will it take to get out of her system? She had been taking it for about 3-4 weeks. Could this small amount( 25 mg) cause her to be sleeping more during the day and not have an appetite? I see that normal doses for allergies are 25-50 mg every 4-6 hours, so would 25 mg once a day have a big effect on someone?
Oct 11, 2022- Benadryl's effects last 4 to 6 hours, but the drug takes 24 to 48 hours to be completely cleared from your system.
- Benadryl can cause drowsiness, dry mouth, blurred vision, and other anticholinergic side effects, and these effects may be stronger and last longer in elderly patients.
- Elderly patients may experience hangover-like effects the morning after taking Benadryl at night, and doctors should be consulted if concerning symptoms occur.
Answer
Thanks for reaching out! First and foremost, Benadryl (diphenhydramine) may certainly be causing some of the side effects you mentioned occurring with your elderly mother. Although Benadryl is relatively short-acting, its effects can be prolonged in the elderly.
Benadryl is an antihistamine that has strong anticholinergic effects, which can cause drowsiness, decreased gut motility, dry mouth, dry eyes, thickening of bronchial secretions, urinary retention, and blurred vision. Benadryl may also cause constipation, diarrhea, or abdominal pain in some patients.
Elderly patients can be especially impacted by the effects of Benadryl. According to the Beers Criteria, Benadryl should be avoided in elderly patients due to the increased risk of confusion, dry mouth, and drowsiness.
How Long Does Benadryl Last?
That brings us to answering specifically how long Benadryl stays in your system.
While the effects of Benadryl generally only last 4 to 6 hours, it takes longer for the drug to be metabolized and eliminated from your system.
In healthy patients, Benadryl has a half-life between 2-8 hours and is cleared completely within 24-48 hours (i.e. one to two days). However, drug clearance in elderly patients can be impacted by the decline in kidney and liver function. Benadryl is extensively metabolized in the liver and dosage reduction may be necessary for patients with liver impairment.
Several studies have shown that some individuals report 'hangover' effects in the morning after Benadryl has been taken at night to help sleep. It isn't overly common, but is more likely to occur in the elderly.
So, it is certainly possible that Benadryl is causing some of the problems you mentioned, however, due to the age of your mother, there certainly could be other things going on. Be sure to talk to your doctor so your mother can be properly evaluated.
What Is Benadryl?
Benadryl is a first-generation antihistamine and is more likely to cause anticholinergic side effects than second-generation antihistamines. Other first-generation antihistamines include Dramamine (dimenhydrinate), Chlor-Trimeton (chlorpheniramine), Tavist (clemastine), and Phenergan (promethazine), among others. These medications cross the blood-brain barrier and have CNS effects like drowsiness and dizziness.
Second-generation antihistamines include Claritin (loratadine), Cetirizine (Zyrtec), and Allegra (fexofenadine) which are much less sedating. Antihistamines are widely used for self-care of allergy symptoms including runny nose, watery eyes, sneezing, and itching of the nose, throat, or eyes. Benadryl may also be used for symptoms of the common cold, allergic reactions, occasional insomnia, and more.
Final Words
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References & sources
- Diphenhydramine: pharmacokinetics and pharmacodynamics in elderly adults, young adults, and children — PubMed
- Next-day residual sedative effect after nighttime administration of an over-the-counter antihistamine sleep aid, diphenhydramine, measured by positron emission tomography — PubMed
- Diphenhydramine Monograph — PubChem
Glossary — Terms in This Answer
- Antihistamine
- A medication that blocks histamine, a chemical in the body that causes allergy symptoms like itching, sneezing, and runny nose.
- Anticholinergic effects
- Side effects that occur when a medication blocks certain nerve signals, causing symptoms like dry mouth, constipation, and urinary retention.
- Gut motility
- The ability of the digestive system to move food and waste through the intestines.
- Half-life
- The amount of time it takes for half of a drug's dose to be removed from your body.
- Metabolized
- The process by which the body breaks down a drug into substances it can eliminate.
- Beers Criteria
- A medical guideline that lists medications that are potentially unsafe for elderly patients.
- Blood-brain barrier
- A protective membrane that controls which substances from the bloodstream can enter the brain.
- CNS effects
- Side effects that affect the central nervous system, such as drowsiness and dizziness.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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