When Does Benadryl Kick In?

Benadryl will begin working within 15-30 minutes.


I want to take Benadryl for sleep and wondering when it will kick in. How soon before bed to take it?

Asked by Phillip On Nov 18, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Nov 19, 2018


Benadryl (diphenhydramine) will start to work about 15 to 30 minutes after taking a dose by mouth.

Therefore, if you are taking it to help you sleep, you should take it about 15 to 30 minutes before your planned bedtime.

However, it is important to note that studies show that peak concentrations in the blood don't occur until 2 to 4 hours after dosing.

So, if using the drug as a sleep aid, the sedative action of Benadryl will begin to take effect 15-30 after taking but maximum effects take longer, anywhere from 1 to 3 hours after administration (1).

If you are looking for the Benadryl product that works the quickest, look for liquid or liqui-gel formulations.

The intramuscular injectable form of diphenhydramine, which is available via prescription only, has a quicker onset of action, within 5 minutes of administration.

Section Summary
Benadryl will 'kick in' about 15 to 30 minutes after administration. Parental forms of Benadryl work faster, within 5 minutes.

Benadryl Information

Benadryl contains the active ingredient diphenhydramine.

It is a 'first-generation' antihistamine, which are noted for their short duration of action and anticholinergic effects.

The anticholinergic effects of Benadryl are largely responsible for the common adverse reactions of the drug, including:

  • Dizziness
  • Sedation
  • Dry mouth
  • Dry eyes
  • Constipation
  • Confusion

Although they share a similar mechanism of action, Benadryl differs from 'second-generation' antihistamines (e.g. Claritin), which last significantly longer and cause far less sedation.

Benadryl is most often used for the treatment of seasonal/perennial allergy symptoms and is commonly used as a night time sleep aid due to its sedative effects.

In fact, diphenhydramine is often the active ingredient in over the counter sleep products, such as ZzzQuil.

Benadryl can be taken with or without food, but if it causes nausea, food can help to alleviate it.

The duration of action is around 4 to 6 hours, although it can certainly have longer lasting effects in certain populations, such as in the elderly or in those with liver disease.

Section Summary
Benadryl contains diphenhydramine, a 'first-generation' antihistamine, which are known for their short duration of action and sedative properties.

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