Diphenhydramine can be used as a short-term sleep aid to help ease occasional sleep problems. Older adults, children under age 16 and pregnant women should avoid taking diphenhydramine, as the risks to these groups may outweigh the benefits.

Diphenhydramine should not be taken as a treatment for chronic insomnia. There is a lack of substantial evidence to support that diphenhydramine provides significant improvement in sleep, including the time it takes to fall asleep, duration of sleep and quality of sleep. Patients also develop a tolerance for the medication after 1 to 2 weeks of taking it, at which point it is no longer beneficial at the same dose.

Why does diphenhydramine make you sleepy?

Some types of antihistamines, including diphenhydramine, have a sedating effect. Antihistamines fight allergies by blocking the action of a chemical called histamine in the brain. Histamines are produced in response to an allergen, but they also play a role in regulating your sleep-wake cycle. By preventing the mechanism of histamines in the brain, some antihistamines can induce drowsiness.

How much should I take? How long does it take to work?

For an occasional bout of insomnia, adults are usually recommended to take 50 mg of diphenhydramine. The effects of the medication will set in around 20 to 30 minutes after taking it, which is why it should be taken approximately 20 minutes before bedtime.

Is it safe to take diphenhydramine every night?

You should not take diphenhydramine every night. While it may be helpful during limited periods of insomnia, your body will build up a tolerance for the medication over time, and it will no longer have the desired effect. After 2 weeks of taking diphenhydramine, you may become dependent on it to fall asleep. Making sure to not take it for more than a couple of days can help prevent you from becoming dependent on it. For chronic insomnia, your doctor can help you find more long-term solutions.