Promethazine is an antihistamine medicine that relieves the symptoms of allergies.

It’s known as a drowsy (sedating) antihistamine. It’s more likely to make you feel sleepy than other antihistamines.

It’s used for:

  • short-term sleep problems (insomnia) – including when a cough or cold, or itching, is keeping you awake at night
  • allergies, including hay fever and hives (urticaria)
  • feeling and being sick (vomiting) – due to morning sickness, travel sickness or vertigo
  • cough and cold symptoms, such as coughing and a runny nose

You can buy promethazine from pharmacies, where it’s often sold as Avomine, Phenergan or Sominex. Promethazine is also available on prescription.

You can also buy promethazine mixed with other medicines, such as paracetamol, dextromethorphan, pholcodine or pseudoephedrine, to treat coughs and colds or pain.

Popular brand names include Day & Night Nurse and Night Nurse.

It comes as tablets, capsules and a liquid that you swallow.

  • Avoid drinking alcohol while taking promethazine. Alcohol increases the risks of side effects.
  • To help you sleep, you’ll usually take promethazine 20 minutes before you go to bed. It normally takes about 30 minutes to work.
  • For preventing travel sickness, you can usually take promethazine the night before a long journey or 1 to 2 hours before a short journey.
  • Common side effects include feeling sleepy, headaches, nightmares and feeling dizzy, restless or confused.
  • Promethazine is known by the brand names Avomine, Phenergan and Sominex.
  • When promethazine is mixed with other medicines, it’s also known by the brand names Day & Night Nurse, Fedril and Night Nurse.

Promethazine can be taken by most adults and children aged 2 years and above.

Promethazine isn’t suitable for some people. Tell your doctor or pharmacist if you:

  • have had an allergic reaction to promethazine or any other medicines in the past
  • have an eye problem called primary angle closure glaucoma
  • have problems peeing or emptying your bladder
  • have epilepsy or any other health problem that causes fits
  • have an intolerance to, or can’t absorb, some sugars, such as lactose or sorbitol
  • are due to have an allergy test. Promethazine can affect your results, so you may need to stop taking it a few days before your test. Ask the clinic where you are due to have your allergy test.
  • are unable to have any alcohol. Some liquid promethazine products contain a very small amount of alcohol, so check the ingredients and the packaging carefully.
  • are trying to get pregnant. Promethazine can affect home pregnancy tests. If you think you’re pregnant, speak to your doctor so they can arrange a blood test instead.

If you or your child have been prescribed promethazine, follow your doctor’s instructions about how and when to take it.

Only take promethazine when you need it – for example, if you’re unable to sleep because you’re worrying about something or your cold symptoms are keeping you awake.

Common side effects

Like all medicines, promethazine can cause side effects, although not everyone gets them.

Talk to your pharmacist or doctor if these side effects bother you or don’t go away:

  • feeling tired during the daytime
  • nightmares
  • feeling dizzy or unsteady on your feet, or having difficulty concentrating
  • headaches

Promethazine can sometimes make your skin more sensitive to sunlight. Keep out of direct or strong sunlight and follow sun safety advice.

If you’re over 65, you’re more likely to experience side effects such as:

  • feeling confused
  • dry mouth
  • blurred vision
  • difficulty peeing

Children are more likely to experience side effects such as feeling restless or excited.

Serious side effects

Call your doctor straight away if you have:

  • yellowing of the skin or whites of the eyes – these can be signs of liver problems
  • bruising or bleeding that’s more than normal
  • muscle stiffness or shaking, or unusual face or tongue movements

Serious allergic reaction

In rare cases, it’s possible to have a serious allergic reaction (anaphylaxis) to promethazine.

What to do about:

  • feeling sleepy during the daytime – this usually wears off 12 hours after a dose. Do not drive or use tools or machinery if you’re feeling this way.
  • nightmares – speak to your pharmacist or doctor if these don’t go away or are troubling you
  • feeling dizzy or unsteady on your feet, or having difficulty concentrating – stop what you’re doing and sit or lie down until you feel better. If the feeling doesn’t go away or is troubling you, do not take any more medicine and speak to a pharmacist or your doctor.
  • headaches – make sure you rest and drink plenty of fluids. Talk to your doctor if the headaches last longer than a week or are severe.

Your doctor may want to prescribe promethazine for morning sickness when other treatments haven’t worked.

Pregnant women have taken promethazine with no harmful effects to the mother or baby. But for safety it’s best to take it for the shortest possible time.

For more information about how promethazine can affect you and your baby during pregnancy, read the leaflet about the best use of medicines in pregnancy (BUMPS).

Promethazine and breastfeeding

Promethazine passes into breast milk in small amounts. Talk to your doctor, as other medicines might be better while you’re breastfeeding.

It’s usually safe to take similar antihistamines like loratadine or cetirizine while you’re breastfeeding.

If you need a drowsy antihistamine to help you sleep, your doctor may recommend chlorphenamine.

But speak to your doctor before taking any antihistamine if your baby was premature, had a low birth weight, or has health problems.

Some medicines and promethazine interfere with each other and increase the chance of having side effects.

Tell your pharmacist or doctor if you’re taking:

  • a type of antidepressant called a monoamine oxidase inhibitor, such as phenelzine
  • any medicine that makes you drowsy, gives you a dry mouth, or makes it difficult for you to pee. Taking promethazine might make these side effects worse.

If you’re taking a cough or cold remedy or a painkiller containing promethazine, check carefully what the other ingredients are.

For example, promethazine often comes mixed with paracetamol. If you take 2 medicines that both contain paracetamol, there’s a risk of overdose.

Ask your pharmacist for advice before you take this medicine together with any other painkillers or medicines.

Mixing promethazine with herbal remedies and supplements

There might be a problem taking some herbal remedies and supplements alongside promethazine, especially ones that cause side effects such as sleepiness, a dry mouth or making it difficult to pee.

Ask your pharmacist for advice.

How does promethazine work?