A sedating antihistamine (trimeprazine)
Alimemazine
A sedating antihistamine used for itchy allergic skin conditions and, because it causes drowsiness, sometimes for short-term sedation.
What is Alimemazine?
Alimemazine (formerly called trimeprazine) is a sedating, first-generation antihistamine. It is used to relieve itchy allergic skin conditions such as urticaria, and its strong drowsiness effect means it is sometimes used for short-term sedation, including before some procedures. Newer non-drowsy antihistamines are usually preferred for everyday allergy.
Education and reference only. This is a plain-language guide to Alimemazine — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Alimemazine is an older antihistamine that crosses into the brain and is quite sedating. In the UK it is used to ease itchy allergic skin problems such as hives (urticaria), and its sedative effect is sometimes put to use for short-term calming or to help with sleep around a stressful event or procedure. It belongs to the phenothiazine family of medicines.
How it works
Alimemazine blocks histamine H1 receptors, reducing the itch and swelling that histamine produces in allergic reactions. Because it is an older medicine it readily enters the brain, which is why it causes marked drowsiness, and it also has some anticholinergic actions that contribute to side effects such as dry mouth.
Company & origin
A first-generation antihistamine of the phenothiazine group, long established in the UK (previously known as trimeprazine).
Practical use
How to take Alimemazine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it exactly as prescribed, with or without food.
- Expect drowsiness — avoid driving or using machinery until you know how it affects you.
- Avoid alcohol, which adds to the drowsiness.
- If used to aid sleep or calming, take it at the time your prescriber advises.
- If you miss a dose, skip it if it is nearly time for the next one — do not take two together.
Weighing it up
Advantages & disadvantages of Alimemazine
Advantages
- Relieves itchy allergic skin conditions and the associated discomfort.
- Reliable sedation can be helpful for short-term, supervised use.
- An established, inexpensive option available as tablets and a liquid.
Disadvantages
- Strongly drowsy, so unsuitable when you need to stay alert and can impair driving.
- Anticholinergic effects such as dry mouth and constipation, especially in older people.
- Not for routine daytime allergy where non-drowsy antihistamines are preferred, and unsuitable for sedating very young children.
Practical use
Good to know
Its main feature is drowsiness, so it is best when you do not need to be alert, and it should not be used when you need to drive or operate machinery. Older people are more sensitive to its sedating and anticholinergic effects and it is used cautiously in this group. It is not suitable for sedating very young children, where sedating antihistamines can occasionally cause unexpected reactions.
Who should not take it / use with caution
- It is not used in children under 2 years old, and sedating antihistamines are generally avoided for young children.
- Avoided in closed-angle glaucoma, urinary retention or significant prostate enlargement, and in significant liver disease.
- Used cautiously in epilepsy, and pregnancy or breastfeeding suitability should be checked with a clinician.
Monitoring
- Whether itch and allergic symptoms settle.
- Daytime drowsiness and anticholinergic effects, particularly in older people.
- Blood pressure and steadiness if dizziness occurs.
Side effects
- Drowsiness, which may carry over into the next day.
- Dry mouth, blurred vision and constipation.
- Dizziness or low blood pressure on standing; occasionally restlessness or, rarely, movement effects typical of phenothiazines.
Key interactions
- Alcohol and other sedating medicines (sleeping tablets, strong painkillers) increase drowsiness.
- Other anticholinergic medicines add to dry mouth, constipation and confusion.
- Care with medicines that affect heart rhythm and with other phenothiazines.
Available as: Tablets, and an oral solution.
Answers
Alimemazine: frequently asked questions
Is alimemazine the same as trimeprazine?
Yes — trimeprazine is an older name for the same medicine. In the UK it is now called alimemazine.
Will it make me sleepy?
Yes, it is one of the more sedating antihistamines. Use it when you do not need to drive or concentrate, and avoid alcohol, which adds to the drowsiness.
Can it be used to calm a child?
It is sometimes used short-term under medical supervision, but it is not recommended for sedating very young children, in whom it can occasionally cause unexpected effects. Always follow a clinician's advice.
Is it safe for older people?
It is used cautiously because older people are more sensitive to its drowsiness, dry mouth, constipation and dizziness, which can raise the risk of falls and confusion.
Why is a sedating antihistamine prescribed when non-drowsy ones exist?
For everyday allergy, non-drowsy antihistamines are usually preferred. Alimemazine is chosen when the sedating or itch-relieving effect is specifically wanted, such as for very itchy skin or short-term calming.
The wider class
About Antihistamines
Alimemazine belongs to the antihistamines class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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