How Long It Takes Benadryl to Work, Plus 4 More Benadryl FAQs

Benadryl (diphenhydramine) is a common over-the-counter (OTC) antihistamine. It can help relieve allergy symptoms, itching, and certain cold symptoms. Some people also use it as a sleep aid since it usually causes drowsiness.

If you decide that you’d like to take Benadryl, talk with your healthcare provider first. Benadryl has several potential interactions and side effects to be aware of. If you do end up taking it, you may find you have some questions about the medication. For instance, many people wonder how long it takes Benadryl to work. In this article, we answer five of the most common questions people have about Benadryl.

1. How long does it take Benadryl to work?

Generally, it takes about 15 to 30 minutes for Benadryl to start working. But the amount of time may vary depending on what dosage form you’re taking and what symptoms you’re treating. Benadryl is available in tablets and capsules that are taken orally, chewable tablets, and an oral liquid. In general, oral liquid medications are absorbed more quickly than tablets or capsules and may start working faster.

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It could take around 2 hours to experience Benadryl’s full effects after taking a dose. So, avoid taking an extra dose even if your symptoms aren’t improving within a few hours. Taking too much Benadryl can be dangerous. If your symptoms aren’t getting better after the first few doses, contact your healthcare provider.

2. How long does Benadryl stay in your system?

For most adults, Benadryl can stay in your system for up to about 60 hours (2.5 days). For children, it doesn’t stick around quite as long. Children retain Benadryl in their bodies for up to about 35 hours (about 1.5 days). But for older adults, Benadryl is present in the bloodstream longer and can last for up to about 90 hours (close to 4 days).

Keep in mind that even though Benadryl stays in your system for a long time, you won’t feel its effects once the amount of the medication in your body drops below a certain level. Generally, the effects of Benadryl should last for about 4 to 6 hours, mirroring the medication’s dosing schedule.

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Regardless of how long Benadryl stays in your system, follow your healthcare provider’s dosing recommendations. These may be different from what’s listed on Benadryl’s label. OTC labels of Benadryl include general dosing instructions, which are safe for most people to follow.

3. How does Benadryl work?

Benadryl works by blocking the effects of a chemical called histamine, which is released by the body to fight off foreign substances.

While histamine can help protect the body against unwanted germs, it’s also responsible for allergy symptoms, such as sneezing, runny nose, and watery eyes. Benadryl and other antihistamines block histamine from working, thus relieving these symptoms.

Benadryl is a first-generation antihistamine. This means it can easily cross into the blood vessels in and around the brain. This is why it often causes drowsiness.

4. When’s the best time to take Benadryl?

There’s not one particular “best time” to take Benadryl. Taking it at night may be preferable for some people. But the timing depends on why you’re taking the medication.

Benadryl can cause drowsiness. So taking it about 30 minutes before bedtime may be a good idea. This would be the best time to take Benadryl if you’re taking it to help with sleep.

But for allergies or itch relief, you may need to take Benadryl a few times throughout the day. In this case, you can take it every 4 to 6 hours as needed for symptoms. Just keep in mind that Benadryl could impair alertness and focus for up to 6 hours after a dose. So make sure you avoid doing activities that require you to be alert, like driving, after taking it.

5. Does Benadryl cause weight gain?

Possibly. Studies have examined whether there’s a link between antihistamines like Benadryl and potential weight gain. But the evidence isn’t clear.

In one study, adults who took an antihistamine like Benadryl tended to have a higher body weight and larger waist circumference than those that didn’t take antihistamines. A small study in children showed a possible link between antihistamine use and an increase in body mass index (BMI).

While these studies note there could be a connection between Benadryl and weight gain, more studies would be needed to say for sure. Keep in mind that occasional antihistamine use is unlikely to cause significant weight changes.

Exercising regularly and eating a healthy diet are good strategies for maintaining a healthy weight. If you’re concerned about potential weight gain with Benadryl, talk to your healthcare provider.

Tips on how to save on Benadryl

There are many ways to save on Benadryl, which is available in both brand-name and generic versions. If your healthcare provider writes you a prescription for OTC Benadryl, GoodRx may be able to help you save over 60% off the average retail price. The price of generic Benadryl at certain pharmacies is as low as $3.01 with a free GoodRx coupon.

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Written by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

Edited by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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