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Diphenhydramine drowsy antihistamine

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 3 minutes read

Diphenhydramine belongs to a family of medications called antihistamines. It is the active ingredient in medications used to treat short-term insomnia for ages 16 years and over. Diphenhydramine can also be found in oral formulations and creams used to relieve bites, stings, and allergic reactions, and in cold and flu preparations to aid with a runny nose and to aid sleep if symptoms are bothersome at nighttime.

Diphenhydramine products are available to purchase from your pharmacy without a prescription.

Doctor’s advice

When would I take a drowsy antihistamine?

Nytol and ZzzQuil are brands of diphenhydramine licensed for short-term use to treat insomnia. If you are temporarily struggling to sleep at night, then the first thing to consider would be some sleep hygiene tips. These include avoiding laptop and phone screens for the hours running up to bedtime, keeping your phone out of the bedroom, running a bath or having a hot drink as part of a going-to-bed routine, and avoiding alcohol or drugs that can cause poor quality sleep.

Sometimes, medications may be needed. Nytol or ZzzQuil can be used short-term if insomnia or lack of sleep becomes distressing. Taking sleep aids like Nytol or ZzzQuil for temporary relief may be beneficial if this is affecting your mental and physical well-being.

How long can I take Nytol or ZzzQuil for?

Since they are licensed for the treatment of short-term insomnia only, they should normally only be used for a maximum of 2 weeks at a time. This is because taking sleeping tablets for extended periods of time may make your insomnia worse. Over extended periods of time, your body can become dependent on sleeping tablets to help you sleep, and you may find you need a higher dose for it to work.

It is best taken sparingly and only as needed. If possible, it may be best to take breaks in-between taking sleeping tablets, for example, only using them 2 - 3 nights a week. Otherwise, stick to the maximum period of 2 weeks of treatment.

If you are still finding it hard to sleep or find you still need to take these sleeping aids after the 2 weeks of treatment, talk to your doctor, who will be able to give you further advice. You may also find it useful to try non-drug therapy to solve the cause of your insomnia, focusing on good sleep hygiene.

How does diphenhydramine work?

Diphenhydramine is an antihistamine that can cause drowsiness by acting on histamine receptors in the brain. It can reduce the time taken to fall asleep and also the depth and quality of sleep. Take it 20 - 30 mins before bedtime; its maximal effect may be experienced after 1 hour. While the medication may help with getting you off to sleep, it can actually reduce the quality of the sleep you get. The medication can cause your body to spend longer in light sleep stages rather than its more restorative deeper sleep. It is useful to help aid sleep when there are temporary disturbances in sleep, such as stress or anxiety.

Diphenhydramine cream and oral formulations help relieve itching, skin rashes, and allergies by opposing the actions of histamine (a chemical released by your immune system during an allergic reaction) by stopping histamine from binding to its target sites in the body.

Diphenhydramine also has an anticholinergic effect which means it opposes the actions of a chemical in the body called acetylcholine. This helps dry up a runny nose during a viral illness such as a cold or the flu.

Are there any side effects?

Common side effects from oral diphenhydramine preparations can include altered mental attention, dizziness, and dry mouth. Therefore, do not drive or operate heavy machinery after taking the medication. Alcohol will enhance the medication's effects, so avoid taking them together. Do not take if you have breathing problems, glaucoma, or an enlarged prostate.

Diphenhydramine cream is less likely to cause side effects. However, sometimes it can increase the sensitivity of your skin to sunlight or cause eczema.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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