How Long Does Benadryl (Diphenhydramine) Last

Our pharmacist answers the latest question regarding how long the antihistamine Benadryl (Diphenhydramine) lasts.

Sep 29, 2017

Cready asked

Hello, knowing that Benadryl can cause drowsiness, I'm wondering for how long. Is the drowsiness 24 hours until the next tablet is taken? For example, if someone takes a benadryl at10pm will the medication still be in effect for 24 hrs and will the drowsiness last that long?or is would it only be through the night when it's irrelevant because the person is sleeping? Thanks.

At a glance

  • For most individuals, Benadryl (diphenhydramine) lasts four to six hours per dose.


Pink Benadryl Tablets

Benadryl (Diphenhydramine) does not typically last 24 hours. That duration of action is associated with the 'second-generation' antihistamines, like Claritin and Allegra.

Each dose of Benadryl will last approximately 4 to 6 hours, but this can vary by individual.

For example, it typically lasts longer in the elderly, which is why it sometimes causes a 'hangover' effect in older individuals if taken as a sleep aid.

Benadryl Duration And Onset

As stated, Benadryl is a fairly short-acting antihistamine, lasting around 4 to 6 hours per dose.

The onset of action is fairly rapid, occurring in 15-30 minutes after taking a dose by mouth, with peak concentrations in the blood occurring after around 2 hours. Therefore, if you are planning on using as a sleep aid, be sure to take it around 15-30 minutes before bedtime.[1][2]

The maximum sedative effect occurs between 1—3 hours after taking the drug.

Benadryl is classified as a "first-generation" antihistamine and has similar characteristics (e.g. short duration of action, sedating) to the other drugs in that class, which include:

  • Tavist (clemastine)
  • Doxylamine
  • Brompheniramine
  • Chlor-Trimeton (Chlorpheniramine)
  1. ^ DrugBank Diphenhydramine Monograph. DrugBank
  2. ^ Elsevier ClinicalKey: Diphenhydramine Monograph. ClinicalKey
  3. ^ Pharmacological Treatment of Insomnia. PubMed

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