Boots WebMD Partners in Health
Return To Boots

Medicines & treatments centre

Terms Of Use


Brand Name(s) : Phenergan, Sominex
Side Effects


Promethazine hydrochloride should be used with caution in:

It should not be used in:

  • People with an allergy to promethazine hydrochloride, or any of its ingredients
  • People who are in a coma
  • People who have severe dizziness, drowsiness or headaches

Also see list of precautions and interactions


Store below 25°C (for oral solution and injection) and store below 30°C (for tablets).

Injection use only: If only part used, discard the remaining solution.

Oral suspension only: Not to be used more than one month after opening.


What is it used for?

  • Promethazine hydrochloride is used to treat allergic conditions, travel sickness and sleeping difficulties.
  • It is a sedating antihistamine, sometimes known as a phenothiazine.
  • It is used to treat allergic conditions, to prevent nausea and vomiting, and to aid relaxation and sleep.
  • In general this drug is used to treat allergic conditions such as hay fever and urticaria and relieve nausea and vomiting due to travel sickness. Hay fever is a condition with inflammation of the nose arising from an allergy to pollen. This leads to cold-like symptoms, such as sneezing, itchiness and a blocked or runny nose. Urticaria is a skin condition, often known as hives or nettle rash. The symptoms of urticaria include a red, itchy rash.
  • Benefits of being on this drug can include a reduction in symptoms associated with hay fever and urticaria in people with these allergic conditions. It also effectively controls symptoms of travel sickness but does cause sleepiness and drowsiness.

Listed below are the typical uses of promethazine hydrochloride.

  • Allergic conditions, such as hay fever and urticaria
  • Allergic reactions to drugs including serious allergic reactions with collapse (anaphylaxis).
  • Prevent travel sickness
  • To aid relaxation before surgery
  • Short-term use as a sedative in both children and adults
  • Short-term use to aid sleep in adults having sleeping difficulties (insomnia)

On occasion your doctor may prescribe this medicine to treat a condition not on the above list.


This medication can be administered in different forms: tablet, oral suspension and injection.

How often do I take it?

  • The use of this medication depends on the reason for the medication.
  • Injection form: This medication will be given to you in the appropriate dose by a doctor or nurse normally by the intramuscular (into a muscle) route.
  • For allergies (tablet and oral suspension form): Take this medication orally usually twice daily, with or without food. If you are given the medication as a single dose it is recommended that you take your medication at night. The oral suspension form is recommended for use in children between two and five years of age,
  • For aiding sleep (tablet and oral suspension form): Take this medication orally as a single dose at night, with or without food. The oral suspension form is recommended for use in children between two and five years of age,
  • For travel sickness (tablet and oral suspension form): Take this medication orally usually the night before travel, with or without food. This medication can then be repeated six to eight hours after initial dose if required. The oral suspension form is preferred for children aged two to ten years of age.
  • Use this medication as required, and as directed in order to get the most benefit from it.
  • Remember to use it at the same time each day - unless specifically told otherwise by your doctor.
  • It may take up to a few hours before the full benefit of this drug takes effect.
  • Certain medical conditions may require different dosage instructions as directed by your doctor.

What dose?

  • Dosage is based on your age, gender, medical condition, response to therapy, and use of certain interacting medicines.

Do I need to avoid anything?

  • This medication may cause drowsiness, blurred vision and decreased awareness, which can seriously impair the ability to drive and operate machinery. This drug may cause drowsiness for up to twelve hours after administration. Alcohol intake should be avoided while taking this medication. Consult your doctor or pharmacist for more details.

When can I stop?

  • Tablet or oral suspension form: use as required, and as directed.
    It should not be taken for more than seven days without seeking medical advice. If your symptoms have not improved, or have got worse after seven days please consult your doctor or pharmacist.
  • Injection form: Always complete the full course as prescribed by your doctor.


  • Sedative effects from drowsiness to deep sleep
  • Dizziness
  • Restlessness
  • Headache
  • Nightmares
  • Tiredness
  • Disorientation
  • Dry mouth
  • Blurred vision
  • Difficulty passing urine
  • Skin rashes, including urticaria (also known as hives, nettle rash), sensitivity to light
  • Problems with the gut including abdominal pain, indigestion, nausea, vomiting, diarrhoea
  • Loss of appetite (which may lead to anorexia)
  • Chest pain
  • Low blood pressure
  • Increased sensitivity to light
  • Confusion, especially in the elderly
  • Injection form only: possible reactions at injection site

If any of these persist or you consider them severe then stop taking the medication and inform doctor or pharmacist.

Tell your doctor immediately if you develop any of the following symptoms:

  • Yellowing of eyes and skin
  • Increased and/or abnormal heart rate
  • Hyperactivity in children
  • Signs of anaemia and other blood disorders (such as long lasting tiredness)
  • Muscle weakness and movement difficulties
  • Uncontrolled muscle spasms, especially in head and face
  • Abnormal movements of the hands, face, neck, tongue and legs (e.g. tremor, twitching)

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

A serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction include: rash, itching/swelling (especially of the face/tongue/throat), dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

The Yellow Card Scheme allows you to report suspected side effects from any type of medicine (which includes vaccines, herbals and over the counter medicines) that you are taking. It is run by the medicines safety watchdog called the Medicines and Healthcare products Regulatory agency (MHRA). Please report any suspected side effect on the Yellow Card Scheme website.


Before taking promethazine hydrochloride, tell your doctor or pharmacist if you are allergic to it; or to other antihistamines; or if you have any other allergies.

This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have:

  • Allergy to promethazine hydrochloride, or any of its ingredients
  • Coma state

Before using this medication, tell your doctor or pharmacist your medical history, especially any of the following:

  • Asthma or bronchitis
  • Bronchiectasis (widening of airways)
  • Severe heart failure
  • Glaucoma (increased pressure in the eyeball)
  • Epilepsy
  • Decreased liver function
  • Decreased kidney function
  • Difficulty passing urine
  • Enlarged prostate gland (prostatic hypertrophy)
  • Certain obstructive diseases of the stomach
  • Reye's syndrome, or signs of the condition (which can include vomiting, confusion and diarrhoea after a viral infection)

Cautions to note:

  • Promethazine may interfere with urine pregnancy tests and produce unreliable results.
  • The use of this medication should be stopped at least 72 hours before having a skin test, as it could make the results unreliable.
  • This medication can make skin more sensitive to light. It is recommended that you avoid strong sunlight while taking this medication.
  • Promethazine may mask the warning signs of ear toxicity caused by drugs such as aspirin and mask the early diagnosis of intestinal obstruction or raised intracranial pressure.

Before having surgery, tell your doctor or dentist that you are taking this medication.

Does alcohol intake affect this drug?

  • Intake of alcohol while on this medication is not recommended.

The elderly: promethazine hydrochloride should be used with caution in the elderly as they may be more likely to get the side effects associated with this medication.

Pregnancy and breastfeeding - please ensure you read the detailed information below


Promethazine hydrochloride is not safe to take if you are, or are planning to become, pregnant.

Third trimester: This medication should be avoided in the last two weeks of pregnancy due to potential effects on the unborn child.

It is sensible to limit use of medication during pregnancy whenever possible. However, your doctor may decide that the benefits outweigh the risks in individual circumstances and after a careful assessment of your specific health situation.

If you have any doubts or concerns you are advised to discuss the medicine with your doctor or pharmacist.


Promethazine hydrochloride is not safe to take if you are breastfeeding.

It is sensible to limit use of medication during breastfeeding whenever possible. However, your doctor may decide that the benefits outweigh the risks in individual circumstances and after a careful assessment of your specific health situation.

If you have any doubts or concerns you are advised to discuss the medicine with your doctor or pharmacist.


Before using this medicine, tell your prescriber of all the medicines you are taking including prescription medicines and medicines you have bought over the counter without a prescription. Tell your prescriber if you are taking vitamins or complementary remedies such as herbal products, as these can also interact with medicines.

If you are taking more than one medicine, these may interact with each other. Your prescriber may decide to use medicines which interact with each other if the benefit outweighs the risks. In these cases, the dose of your medicines may need to be adjusted or you may be monitored more closely.

The following may interact with promethazine:

  • Monoamine oxidase inhibitors (MAOIs) or within two weeks of stopping (used to treat mental health problems, e.g. phenelzine, isocarboxazid)
  • Alcohol
  • Tricyclic antidepressants, such as amitriptyline, imipramine
  • Medicines used for sleeping and anxiety problems, such as zopiclone, diazepam and nitrazepam
  • Antipsychotics, such as haloperidol, chlorpromazine, clozapine, used in the treatment of certain mental health problems
  • Opioid analgesics (used for pain) such as morphine, codeine, dihydrocodeine
  • Sedating antihistamines (for allergies) such as hydroxyzine, chlorphenamine, brompheniramine
  • Other medicines with anticholinergic effect, such as medicines for irritable bowel syndrome (e.g. hyoscine), asthma, bladder weakness (e.g. oxybutynin, flavoxate)
  • Medicines to lower blood pressure
  • Aspirin

This information does not contain all possible interactions. Therefore, tell your prescriber of all the products you are using before taking this medicine.

If you have a question or want to discuss anything about your medicine, speak to your local pharmacist.


If you or your child takes more than you should, tell a doctor or go to the hospital casualty department straight away. Take the medicine pack with you. This is so the doctor knows what you or your child has taken.

Symptoms of overdose in children may include: excitation, decreased co-ordination and balance, abnormal and involuntary movements, hallucinations, convulsions (fits), increased and/or abnormal heart rate and slow breathing

Symptoms of overdose in adults may include: drowsiness, which can lead to a coma, convulsions (fits), increased and/or abnormal heart rate and slow breathing.

If you think you, or someone you care for, might have accidentally taken more than the recommended dose of promethazine hydrochloride or intentional overdose is suspected, contact your local hospital, GP or if in England call 111. In Scotland call NHS 24. In Wales, call NHS Direct Wales. In the case of medical emergencies, always dial 999.


For use to treat an allergic condition: If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

For aiding sleep: Skip the missed dose and take medication as usual the following evening.

Find a medication

Search by medication name for information on over-the-counter or prescription medications including side effects and interactions.
indicates detailed medicines information

Source: Selected from data included with permission and copyrighted by Boots UK Limited. This copyrighted material is sourced from a licensed data provider and is not for distribution, except as may be authorised by the applicable terms of use.
CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgement of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse events, nor should it be construed to indicate that use of a particular medicine is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any medicine, changing any diet, or discontinuing any course of treatment.

Search for a medicine or treatment

Search by medicine name or treatment for information including side effects and interactions.

Ex. Simvastatin, Ibuprofen, Amitriptyline Hydrochlorine

Popular slideshows & tools on BootsWebMD

How to help headache pain
rash on skin
Top eczema triggers to avoid
Causes of fatigue & how to fight it
Tips to support digestive health
woman looking at pregnancy test
Is your body ready for pregnancy?
woman sleeping
Sleep better tonight
Treating your child's cold or fever
bucket with cleaning supplies in it
Cleaning and organising tips
adult man contemplating
When illness makes it hard to eat
woman holding stomach
Understand this common condition
cold sore
What you need to know