Promethazine – Versatile antihistamine for allergies, nausea, and sleep.
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What is Promethazine?
Promethazine (brand name Phenergan) is a versatile antihistamine medication with sedating properties. It’s used to treat allergic reactions, prevent motion sickness, control nausea and vomiting, and provide short-term relief from sleep problems.
Book an online consultation if you’re experiencing allergic reactions, travel sickness, or short-term sleep difficulties. Our GPs can assess your symptoms and determine if Promethazine is the right treatment for your specific needs.
What is Promethazine used for?
- Allergic reactions and hay fever
- Motion sickness and travel nausea
- Nausea and vomiting
- Short-term sleep problems (insomnia)
- Sedation before medical procedures
- Severe itching (urticaria)
- Cough suppression (occasionally)
How does Promethazine work?
A phenothiazine antihistamine that blocks histamine receptors and has sedating properties, reducing allergic reactions, nausea, and promoting sleep.
Dosage and Administration
Adults
10-25 mg taken 2-4 times daily, or 25-50 mg at bedtime for sleep. Maximum 100 mg daily.
Children
Children over 2 years: 5-15 mg daily in divided doses—specialist advice required for under 2s.
Important Notes
- Can be taken with or without food.
- For motion sickness: take 1-2 hours before travel.
- For sleep: take 20-30 minutes before bedtime.
- Start with the lowest effective dose.
Side Effects
Common Side Effects
- Drowsiness and sedation
- Dry mouth
- Blurred vision
- Dizziness
- Constipation
- Confusion (especially in elderly)
- Urinary retention
Serious Side Effects
Seek immediate medical attention if you experience:
- Severe breathing depression
- Uncontrollable muscle movements
- Severe allergic reactions
- Liver problems
- Blood disorders
- Severe skin reactions
Important Warnings
- May cause severe drowsiness—do not drive or operate machinery.
- Avoid alcohol as it increases sedation and breathing depression.
- Not suitable for children under 2 years due to risk of breathing problems.
- Use with caution in elderly patients—increased risk of falls and confusion.
- Tell your GP if you have breathing problems, heart disease, or glaucoma.
Drug Interactions
Tell your GP if you're taking any of the following medications:
- Alcohol—dangerous increase in sedation and breathing depression.
- Opioid painkillers—increased risk of breathing problems.
- Other sedating medications—additive drowsiness effects.
- MAOIs—may increase side effects.
- Anticholinergic drugs—increased risk of dry mouth, constipation, confusion.
Frequently Asked Questions
How long does the drowsiness last?
Drowsiness can last 8-12 hours or longer. Avoid driving or important tasks the next day if you took it for sleep.
Can I take Promethazine every night for sleep?
It's only for short-term sleep problems (2-3 nights maximum). Regular use can lead to dependence and reduced effectiveness.
Is it safe to give to young children?
Not recommended for children under 2 years due to serious breathing risks. For older children, use only under medical supervision.
Why do I have a dry mouth and blurred vision?
These are anticholinergic effects that are common with promethazine. They usually improve as your body adjusts to the medication.
Medically Reviewed by: Mohammed Hassan - Independent Prescriber
Last Updated: 2025-01-14