Your Guide to Using Promethazine for Sleep

Written by
The Manual Team
Medically approved by
Dr Earim Chaudry
Last updated
6th March 2022

In 30 seconds

Promethazine is a drowsy antihistamine that is proven to help insomnia. It works by blocking the chemical histamine that promotes feelings of wakefulness. Using promethazine for sleep is highly effective but, unlike other sleep aids, it has the benefit of not being addictive. However, when taking the medicine, it is important that you follow the recommendations for use – as it can have side effects.

An Alternative to Conventional Sleep Medication

There are so many sleep aids out there. But while they can be incredibly effective, many can be addictive and even dangerous when not used properly.

You shouldn’t have to risk your health to improve your sleep. Alongside the likes of the natural hormone melatonin, promethazine – a type of antihistamine – has been found to deliver incredible results without the risk of addiction.

Here, we want to tell you all about using promethazine for sleep – from how it works to how to take it.

What is Promethazine?

Promethazine – or promethazine hydrochloride – is what is known as a drowsy antihistamine. Yes, that’s the type of drug most commonly associated with the treatment of allergies. But this particular type of antihistamine has been found to encourage feelings of drowsiness and promote the onset of sleep.

That’s why it’s used as a treatment for short-term sleep problems. In fact, you might know promethazine already, as it is used in cold and flu medications such as Night Nurse. But this active ingredient is also available as a standalone medication – often with the brand name Phenergan.

In the UK, you can get promethazine over the counter, but it can also be prescribed by the NHS. In both cases, you might receive the medicine as a tablet, capsule, or a liquid.

How Does Promethazine Work?

Promethazine works as a sedative by blocking the chemical in your body known as histamine.

While most often associated with allergies such as hay fever, histamine plays an important role in the sleep-wake cycle too. Specifically, studies show histamine to be responsible for a state of vigilance and alertness when you are awake.

What promethazine does is block this chemical. That means that any feelings of alertness fade and you become more relaxed. This way, sleep comes much more easily.

For people with insomnia, promethazine is highly effective. Studies have shown that promethazine can increase sleep time, reduce night-time awakenings, and improve perceived sleep quality.

Note. Promethazine is also prescribed for other health conditions, including motion sickness, vertigo, hay fever and hives, nausea, and cold symptoms.

How to Take Promethazine for Sleep

Promethazine is a medicine, and with all medicines you need to make sure you take it properly. Make sure you follow the instructions that are included on the pack.

Here are the details you need to know:

  • Promethazine usually comes in 25mg tablets. 10mg and 50mg doses are also available.
  • Take promethazine about 20 to 30 minutes before going to bed. It takes about half an hour before feelings of sleepiness kick in.
  • Swallow the tablets whole. Don’t chew them, as this can affect the way the medicine is absorbed. The best way to take the tablets is with a glass of water, to ensure that you swallow them easily.
  • Don’t take more than the recommended dose, and don’t take two doses at the same time. This can increase your risk of side effects (more on those below).
  • Avoid alcohol when taking promethazine, as it increases the chance of side effects too.
  • You can take promethazine with some other natural sleep supplements. Our Good Nights supplements contain chamomile, lemon balm, and tart cherry, to help feelings of relaxation and tiredness.

All sleep medicines work best when combined with a healthy, active lifestyle that is conducive to sleep. Exercising regularly, cutting down on alcohol and caffeine, and creating an optimal environment for sleep will all help. 

Find out more: How to Sleep Better: 20 Essential Tips

Who Should Not Take Promethazine?

Promethazine is generally a safe, non-addictive, and highly effective sleep aid. However, like any medicine, it is not for everyone. That’s because it can be affected by other medical conditions, as well as by some medications.

Before you take promethazine, talk to a doctor if any of the following apply to you:

  • You have glaucoma, problems urinating, epilepsy, or another condition that causes seizures.
  • You are trying to get pregnant. Promethazine can be used during pregnancy and while breastfeeding, but talk to your doctor first.
  • You are not allowed alcohol. Many promethazine products contain alcohol in small quantities.
  • You are taking a type of antidepressant such as phenelzine (or another monoamine oxidase inhibitor).
  • You are taking opioid painkillers (such as codeine).
  • You are taking any medication that gives you a dry mouth, makes it harder to urinate, or makes you drowsy. Promethazine can make all of these side effects more likely.

What are the Side Effects of Promethazine?

All medicines can cause side effects. Promethazine is no exception. These are the promethazine side effects you should look out for:

  • Tiredness during the day
  • Nightmares
  • Headaches
  • Dizziness

Older people may also experience:

  • Confusion
  • Blurred vision
  • Dry mouth
  • Difficulty urinating

If you experience any of the following serious side effects, immediately seek medical advice:

  • Jaundice, where your skin or the whites of your eyes turn yellow
  • You bruise or bleed more easily
  • You feel very stiff or experience unusual face or tongue movements
  • You have an allergic reaction – or you have breathing problems, heart palpitations, or develop a serious rash.

If you have taken promethazine, do not drive anywhere, even to the hospital. It can be extremely dangerous if you are feeling drowsy or sleepy.

Key Takeaways

Many people already successfully use promethazine for sleep. It is known as a highly effective and non-addictive option for people who have trouble sleeping. And it could help you get a good night’s sleep too.

At Manual, we can help you make sleep problems a thing of the past. Get in touch with us to find out the best option for you.


How Long Does It Take for Promethazine to Work?

Usually, promethazine works within half an hour of when you take it. It is recommended that you take it about 20 to 30 minutes before bedtime.

It is really important that you do not take a second dose if you don’t feel the effects within half an hour. You may increase your chance of side effects.

Is It Bad to Take Phenergan Every Night?

Phenergan and promethazine in general are licensed for the short-term treatment of sleep problems. That means that if you want to take these medications every night, it is best to talk to your doctor first.

While there is no evidence that it will do you any harm, it may reduce the effect of the medication in the long term.

While we've ensured that everything you read on the Health Centre is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. It should never be relied upon for specific medical advice. If you have any questions or concerns, please talk to your doctor.

Further reading

From our health centre. Experts, information and hot topics. See all Sleep articles

Sleep by Manual

Get better sleep with Manual

Clinically proven treatments and expert guidance for better sleep, delivered to your door.