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Phenergan is an antihistamine medication that is commonly used to treat allergic reactions, sometimes to treat nausea and also for sleeping problems. This medicine works by blocking the histamines in the body that cause an allergic reaction. Phenergan is the brand name for promethazine hydrochloride and comes in the form of tablets or a syrup.

What is Phenergan?

Phenergan, which belongs to the group of medicines known as phenothiazines, is an antihistamine used to treat allergies, prevent nausea and help with sleeplessness. It is sometimes used post-surgery to help deal with the sickness which can occur after a general anaesthetic. It can also be given before an operation to help the patient feel more relaxed.

Antihistamine medication blocks the histamines that the body releases naturally as a reaction to an allergy. Histamines are chemicals that cause the body to fight allergens (the substances that cause the allergic reaction).

Allergic reactions

When an allergic reaction occurs, the body activates its defence system to fight the allergy. If a person comes into contact with something they are allergic to, the immune system reacts. The body produces histamines which cause the symptoms of the allergic reaction.

These symptoms are typically:

  • Runny nose;
  • Sneezing;
  • Itchy skin (hives);
  • Blocked nose;
  • Itchy mouth;
  • Watery eyes.

An antihistamine such as Phenergan can stop the symptoms of an allergic reaction by preventing the histamines in the body from joining to its receptors. Common allergies that result in an allergic reaction are insect bites, pollen, dust mites and pet dander (not animal hair as is often believed). Antihistamines are also used to treat hay fever, which is a common problem for many people and occurs when the immune system has a reaction to allergens in the air. Many of the symptoms are those listed above.


Phenergan can also block the receptors in the brain that cause the desire to be sick. When sickness occurs, the brain receives messages from the inner ear telling the body to expel the vomit. Phenergan is used to treat different kinds of sickness including travel (or motion) sickness, which occurs when you feel unbalanced due to travelling in a vehicle or on a boat. Phenergan can also be used to treat morning sickness (when you are pregnant, especially in the early stages).

However, it should not be used during the last six months of pregnancy and if taken in the first trimester, should only be used for the shortest time possible under supervision from a doctor.


Phenergan causes drowsiness and can make you feel more relaxed, and as such can be used as a short-term solution to being unable to get to sleep, for example due to anxiety or a cough or cold. It is not a long-term sleeping medication. If you often have problems sleeping, you should consult a doctor.

When is Phenergan used?

Phenergan is used to treat allergic reactions, some forms of sickness (morning sickness and travel sickness), occasional difficulty sleeping, pre-operative nerves and sometimes for post-operative sickness. It can be used as an antihistamine for allergies and travel sickness in children over two years of age on the advice of a doctor or pharmacist. Phenergan should not be given to children under two years old. For sleeplessness, Phenergan should only be taken by adults and is not a long- term solution to insomnia.

How do you use Phenergan?

Phenergan comes in both tablet and syrup form. The tablets are 10 mg or 25 mg and are swallowed whole with a glass of water, with or without food. Do not chew the Phenergan tablets. The syrup can be accurately measured using the dosage beaker, spoon or syringe supplied in the pack to ensure the correct dose is taken. If Phenergan is used for travel sickness, it should be taken 30–60 minutes before the journey begins. If it is taken for allergies, it is taken as soon as the reaction occurs. For sleeplessness, you should take one 25 mg tablet up to an hour before going to bed to allow it time to work. It should only be used for occasional sleeping problems. If you are unable to sleep consistently you should talk to your doctor.

What dosages are there?

Phenergan is available in dosages of 10 mg or 25 mg tablets and a syrup of 5 mg/5ml 100 ml.

The usual dosages are:

  • Allergies: 12.5 mg twice a day (half a 25 mg tablet) or 25 mg once a day;
  • Vomiting and nausea (including morning sickness): 25 mg every hour as required;
  • Travel sickness: 25 mg twice a day.

However, please note that these are only usual dosages. It is important you follow the advice of your doctor or pharmacist when taking Phenergan as they may recommend a different dose that suits your individual situation. Phenergan must not be given to children under two years of age. Children aged two and over may be given Phenergan liquid (in syrup form). When taking Phenergan liquid, you must use the plastic measuring beaker, syringe or spoon supplied. Do not use a kitchen teaspoon as this will not measure the correct amount accurately.

What are the side effects of Phenergan?

As with all medicines, Phenergan can have some side effects. What symptoms may occur and their extent will depend on the individual person. Some people may experience one or more side effects while others may not experience any. People over 65 years of age are more likely to experience side effects. It is possible that this medicine can cause children to become over-excited or restless.

Possible side effects include:

  • Drowsiness;
  • Nausea and vomiting;
  • Dizziness;
  • Difficulty urinating;
  • Dry mouth;
  • Constipation;
  • Headaches;
  • Confusion;
  • Nightmares;
  • Blurred vision.

If you experience any of the above symptoms while taking Phenergan tablets or Phenergan liquid, you should discuss them with your doctor or pharmacist. It is also important to inform your doctor of any other medications you may be taking before commencing with Phenergan, including herbal medicines.

Occasionally Phenergan can make your skin more sensitive to sunlight than usual. For this reason, it is advisable to stay out of direct sunlight whilst taking this medicine. If you are not taking Phenergan to help with sleeping but it makes you feel drowsy, you should not operate machinery or drive until this feeling passes. It can take up to 12 hours after taking a dose of Phenergan for the drowsiness to wear off. This also applies if Phenergan makes you unable to concentrate or unaware of your surroundings. If Phenergan makes you feel dizzy you should sit or lie down until the feeling passes. If you experience headaches while taking Phenergan, you should drink plenty of water and rest. For a full list of potential side effects, please refer to the medicine leaflet.

When should you not use Phenergan?

You should not use Phenergan if you are allergic to any of the ingredients listed on the package leaflet.

Children under two years of age should not be given Phenergan liquid or Phenergan tablets.

You should only use Phenergan for morning sickness if you are pregnant on the advice of a doctor. You should not take Phenergan during the last six months of pregnancy as it could harm the unborn baby. To be completely safe, it is advisable to take Phenergan for morning sickness for the shortest possible time. You should not take Phenergan if you are breastfeeding as it passes into the breast milk. If you are trying to become pregnant, it is important you tell your doctor this before taking Phenergan as they may advise against it.

Be aware that if you are taking Phenergan for sickness or allergies, it could make you feel tired or sleepy.

Phenergan should not be taken long-term and should only be used on the advice of a doctor or pharmacist.

Where can you buy Phenergan?

You can buy Phenergan at a pharmacy without a prescription. You should follow the advice of a pharmacist or doctor before taking Phenergan.

Can I get Phenergan without a prescription?

Yes. Phenergan is both a prescription and non-prescription medication. It should be taken on the advice of your doctor or pharmacist.


Do I Need Antihistamines for Allergies? (n.d.) Retrieved 8 May 2019 from

Marshall,H. (28 February 2019). Phenergan (promethazine): an antihistamine for allergies, travel sickness and sleep. Retrieved 9 May 2019 from

Package leaflet. PHENERGAN 0.06% Gel. Oestradiol. June 2007. Retrieved 30 April 2019 from 1510756508.pdf?_ga=2.7831730.1442913771.1601361456-2071352208.1599043266

Promethazine (including Phenergan). 18 September 2018. Retrieved 9 May 2019 from

Reviewed by:

Dr Imran Malik, General practitioner Registrationnumber: GMC: 4741365 Last checked: 18-11-2022 | Still valid

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