Promethazine

Promethazine (brand names Phenergan, Avomine, Sominex) is an antihistamine medicine that relieves the symptoms of allergies.[1] Promethazine sometimes comes mixed with other medicines, such as paracetamol, dextromethorphan or pseudoephedrine, to treat coughs and colds or pain.[1]

It comes as tablets, capsules or as a liquid that is swallowed. It is known as a drowsy (sedating) antihistamine, so it is more likely to make people feel sleepy than other antihistamines.[1]

This medicine can cause serious allergic reactions which require emergency treatment. Make sure the signs of these reactions are known: read allergic reaction symptoms of drugs.

Do not drink alcohol while taking promethazine.[1] Alcohol increases the risks of side effects. Promethazine is taken 20 minutes before bed to help with sleep. It normally takes about 30 minutes to work. To prevent motion sickness, it is taken the night before a long journey or 1 to 2 hours before a short journey.[1]

Who can and cannot take promethazine

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.[1]

Some types of promethazine medicines are not suitable for children over 6. Some are labelled 12+ and some are labelled 16+. The doctor or pharmacist will advise which are the safest for children.[1]

Promethazine is not suitable for some adults. To make sure it is safe, tell a doctor or pharmacist if there is new or has ever been:[1]

  • allergic reactions to promethazine or any other medicine
  • an eye problem called primary angle closure glaucoma
  • problems peeing or emptying the bladder
  • epilepsy or any other health problem that causes seizures or fits
  • are due to have an allergy test. Promethazine can affect the results, so it may need to be stopped for a few days before the test. Ask the clinic where the allergy test is due
  • 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 pregnancy is suspected, speak to a doctor so they can arrange a blood test instead

If buying promethazine or any medicine containing promethazine from a pharmacy, follow the instructions that come with it, or ask a pharmacist for advice

Dosage and strength

Promethazine comes in 10mg, 20mg and 25mg tablets. The dose depends on why it is being taken:[1]

  • short-term insomnia
    • usually, 20mg to 50mg at night
  • hay fever
    • usually, from 10mg twice a day to 20mg, 3 times a day
  • hives
    • usually, from 10mg twice a day to 20mg 3 times a day
  • preventing motion sickness
    • usually, 25mg 1 to 2 hours before a short journey or 25mg the night before a long journey
  • treating motion sickness
    • 25mg as soon as possible and 25mg the same evening, followed by 25mg the following evening (if needed)
  • vertigo
    • the dose can vary from 25mg a day to 25mg 4 times a day

If taking liquid which contains 5mg of promethazine in 5ml, follow the instructions that come with the medicine for how much to take.[1]

Doses are lower for children. The doctor will use the child's age to work out the right dose.[1]

Promethazine mixed with other medicines

Promethazine can come mixed with other medicines, such as paracetamol. This is usually used to treat cough and cold symptoms. The dose will depend on the type of medicine being taken.[1]

Check the instructions on the packaging carefully, or ask a pharmacist or doctor if ever unsure.[1]

Side effects

Common side effects

Like all medicines, promethazine can cause side effects, although not everyone gets them.[1]

Talk to a pharmacist or doctor if these side effects are a bother or do not go away:[1]

  • feeling tired during the daytime
  • nightmares
  • feeling dizzy or unsteady on one's own feet, or having difficulty concentrating
  • headaches

Promethazine can sometimes make the skin more sensitive to sunlight. Keep out of direct or strong sunlight and follow sun safety advice.[1]

In people over 65, they are more likely to get side effects such as:[1]

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

Talk to a doctor or call non-emergency services straight away if these side effects show up.[1]

Children are more likely to get side effects such as feeling restless or excited.[1]

Serious side effects

Call a doctor straight away if:[1]

  • whites of the eyes or the skin turn yellow (although this may be less obvious on black or brown skin). These can be signs of liver problems
  • noticing more bruising or bleeding than normal
  • muscle stiffness or shaking, or unusual face or tongue movements

Serious allergic reaction

In rare cases, it is possible to have a serious allergic reaction (anaphylaxis) to promethazine.[1]

Other side effects

These are not all the side effects of promethazine. For a full list, see the leaflet inside the medicine packet.[1]

Pregnancy and breastfeeding

Promethazine and pregnancy

Promethazine can be used in pregnancy. There is no good evidence that it is harmful to a baby, but it can have side effects such as drowsiness.[1]

For the treatment of hay fever, a doctor or pharmacist may recommend a non-drowsy antihistamine (loratadine).[1]

Promethazine and breastfeeding

If the doctor or health visitor says your baby is healthy, promethazine can be used during breastfeeding. If prescribed promethazine, it is better to take occasional doses or only for a short time.[1]

It is 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 baby sleepy too. It may also reduce the amount of milk that is produced.[1]

If breastfeeding or planning to breastfeed, talk to a doctor or pharmacist, as other medicines might be better while breastfeeding.[1]

If baby is not feeding as well as usual, seems unusually sleepy, or seems irritable, or if there are any other concerns about baby, talk to the doctor, pharmacist, health visitor or midwife.[1]

Tell a doctor if trying to get pregnant, are already pregnant, or breastfeeding.[1]

Cautions with other medicines

Some medicines and promethazine can affect each other and increase the chance of having side effects.[1] Tell a pharmacist or doctor if taking:[1]

If 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 2 medicines that both contain paracetamol are taken, there is a risk of overdose.[1]

Ask a pharmacist for advice before taking this medicine together with any other painkillers or medicines.[1]

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.[1]

Ask a pharmacist for advice.[1]

Tell a doctor or pharmacist if taking any other medicines, including herbal medicines, vitamins or supplements.[1]

References
  1. "Promethazine: drowsy (sedating) antihistamine that relieves allergy symptoms". nhs.uk. 2018-09-20. Retrieved 2024-06-14.
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