Promethazine at a glance
Medicine class
Sedating antihistamine and phenothiazine derivative.
Alertness
Often causes sleepiness; do not drive or operate machinery if affected.
Alcohol
Avoid alcohol because it can markedly increase sedation and impair breathing or waking.
Food
Oral promethazine can be taken with or without food.
What is Promethazine used for?
Licensed uses vary by product and formulation.
Allergic conditions affecting the upper airways or skin, including allergic rhinitis and urticaria.
Prevention or treatment of nausea and vomiting, including travel sickness where licensed.
Temporary sleep disturbance in adults where licensed.
Sedation in children where the product and age restrictions permit.
The injection may be used for sedation and as an adjunct to preoperative sedation in surgery or obstetrics.
How does Promethazine work?
Promethazine blocks histamine H1 receptors, reducing allergy symptoms. It enters the brain, causing sedation and helping suppress nausea. Its anticholinergic activity contributes to effects such as dry mouth, blurred vision, constipation and urinary difficulty.
Promethazine preparations and strengths
Tablet
Route: Oral
Strengths: 25 mg
Injection
Route: Parenteral
Strengths: 25 mg/mL
How to take Promethazine
Follow the prescription or instructions for the exact product because suitability differs by indication, formulation and age.
Tablets may be taken with or without food, swallowed whole with water and not chewed.
Use the supplied oral syringe or medicine spoon for liquids, not a kitchen teaspoon.
The injection must be prepared and administered by a healthcare professional. Intravenous administration requires dilution and particular care to prevent serious tissue injury.
Check combination cough, cold or pain products to avoid duplicate active ingredients.
Promethazine side effects
Common or expected effects
- Daytime sleepiness or tiredness
- Dizziness, unsteadiness or difficulty concentrating
- Headache
- Nightmares
Get urgent medical advice
- Difficulty breathing or swelling of the face, mouth, tongue or throat
- Fast, pounding or irregular heartbeat
- Severe confusion, unusual movements, muscle stiffness or shaking
- Yellow skin or eyes
- Unusual bruising, bleeding, fever, sore throat or other signs of a blood disorder
- Difficulty passing urine
Promethazine in pregnancy
UK patient information states that promethazine can be used during pregnancy and available evidence does not suggest harm to the unborn baby. Selected product information recommends an individual benefit–risk assessment, particularly near delivery. Tell the prescriber or pharmacist if pregnant or planning pregnancy.
Promethazine while breastfeeding
Breastfeeding guidance and selected product information differ, so seek professional advice before use. If used while breastfeeding a healthy, full-term baby, monitor for unusual sleepiness or irritability, poor feeding, dry mouth, abnormal movements and inadequate weight gain. Repeated use may affect milk production.
Promethazine interactions
Ask a pharmacist or prescriber to check all medicines, including non-prescription and herbal products.
Alcohol, opioids, sleeping medicines and other sedatives
Sedation and impairment can be substantially increased, with a risk of respiratory depression.
Monoamine oxidase inhibitors
Selected products advise avoiding promethazine during and after MAOI treatment as specified in the product information.
Common questions about Promethazine
Answers are fully visible for fast scanning and source review.
Does promethazine hydrochloride make you sleepy?
Yes. Sedation may persist into the following day. Do not drive, cycle or use machinery if sleepy, dizzy, visually impaired or unable to concentrate.
Can I drink alcohol while taking promethazine hydrochloride?
No. Alcohol can markedly deepen sedation and may make breathing or waking difficult.
Can children take promethazine hydrochloride?
Suitability and minimum age depend on the product and reason for use. Serious respiratory and central nervous system effects can occur in young children, so check the leaflet and obtain professional advice.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.