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

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

Promethazine is used for:

• short-term sleep problems (insomnia) – including when a cough, cold or itching is keeping you awake at night
• allergies, including hay fever and hives (urticaria)
• feeling and being sick (vomiting) – due to motion sickness or vertigo
• 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.

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

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

• Do not drink alcohol while taking promethazine. Alcohol increases the risks of side effects.
• To help you sleep, take promethazine 20 minutes before you go to bed. It normally takes about 30 minutes to work.
• To prevent motion sickness, take promethazine the night before a long journey or 1 to 2 hours before a short journey.
• Common side effects of promethazine include drowsiness, headaches, nightmares and feeling dizzy, restless or confused.
• When promethazine is mixed with other medicines, it's also known by the brand names Fedril and Night Nurse.

Promethazine can be taken by most adults.

Children under 6 should not be given cough and cold medicines containing promethazine if they have been bought at a pharmacy. These medicines should only be given if prescribed by a doctor.

Some types of promethazine medicines are not suitable for children over 6. Some are labelled 12+ and some are labelled 16+. Your doctor or pharmacist will advise which are the safest for children.

Promethazine is not suitable for some adults. To make sure it's safe for you, tell your doctor or pharmacist if you:

• have ever had an allergic reaction to promethazine or any other medicine
• 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 seizures or fits
• 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.

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 do not 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 get side effects such as:

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

Talk to a doctor or call 111 straight away if you have these side effects.

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

What to do about:

• feeling sleepy during the daytime – this usually wears off 12 hours after a dose. Do not drive, cycle or use tools or machinery if you're feeling this way.
• nightmares – speak to your pharmacist or doctor if these do not 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 does not go away or is troubling you, do not take any more medicine and speak to a pharmacist or 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.

Promethazine can be used in pregnancy. There is no good evidence that it is harmful to your baby, but it can have side effects such as drowsiness.

For the treatment of hay fever your doctor or pharmacist may recommend a non-drowsy antihistamine (loratadine).

Promethazine and breastfeeding

If your doctor or health visitor says your baby is healthy, promethazine can be used during breastfeeding. If you are prescribed promethazine, it's better to take occasional doses or only for a short time.

It's not known how much promethazine passes into breast milk but it is likely to be a small amount. It has been used for many years without causing babies to have side effects. However, promethazine is a drowsy antihistamine, so may also make your baby sleepy too. It may also reduce the amount of milk you produce.

If you're breastfeeding or planning to breastfeed, talk to your doctor or pharmacist, as other medicines might be better while you're breastfeeding.

If your baby is not feeding as well as usual, seems unusually sleepy, or seems irritable, or if you have any other concerns about your baby, talk to your doctor, pharmacist, health visitor or midwife.

Find out more about how promethazine can affect you and your baby during pregnancy on the Best Use of Medicines in Pregnancy (BUMPs) website.

Some medicines and promethazine can affect 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
• a type of painkiller called an opioid, such as codeine, morphine or oxycodone
• 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.