Phenergan is a well known UK brand of promethazine hydrochloride. It is licensed for several uses, including short term insomnia in adults, allergy symptoms and nausea or vomiting such as travel sickness. The dose can change depending on your age, the formulation you are using and why you are taking it.
This guide explains the licensed Phenergan doses for adults and children using the UK Summary of Product Characteristics (SmPC), the patient information leaflets and NHS guidance. The information is for reference and does not replace advice from your prescriber or pharmacist. Always follow the instructions that come with your particular medicine.
Quick Answer: Phenergan Dose for Sleep
For adults and children over 10 years, the licensed Phenergan dose for short term insomnia is 25mg or 50mg as a single dose at night. With Phenergan 25mg tablets, this means one or two tablets. With Phenergan Elixir, 25mg to 50mg is equivalent to 25ml to 50ml, although the product information recommends Phenergan tablets for adults and children over 10 for these doses.
Key takeaways
- The licensed night time dose for adults and children over 10 is 25mg or 50mg as a single dose.
- For adults, 25mg or 50mg is the licensed range. Do not increase the dose yourself if 25mg does not seem to work.
- Oral Phenergan is contraindicated in children under 6 years of age.
- Promethazine can cause significant drowsiness, and its effects may last for several hours. The product information states that the duration of action may be up to 12 hours.
- Phenergan should not be taken for longer than 7 days without medical advice.
What Phenergan Is and How Promethazine Works
Phenergan contains promethazine hydrochloride, a sedating antihistamine from the phenothiazine group. Unlike some newer antihistamines, promethazine can make you sleepy because it acts on the central nervous system.
Promethazine blocks the effects of histamine and also has anticholinergic and antiemetic effects. This helps explain why it can be used for allergy symptoms as well as nausea and vomiting linked to motion sickness and vertigo.
It is also used for short term insomnia in adults. However, feeling sleepy is an effect of the medicine rather than a treatment for the underlying cause of ongoing sleep problems.
How quickly it works and how long it lasts
There is no specific onset time stated in the current UK Phenergan product information. Some information about promethazine gives an onset of around 20 minutes, but that figure should not be treated as a guaranteed time for Phenergan tablets or elixir.
The Phenergan product information states that the duration of action may be up to 12 hours. This is particularly important if you take it at night, because you may still feel sleepy, dizzy or have blurred vision the following morning.
If Phenergan affects your alertness, do not drive, cycle or operate machinery.
Phenergan Strengths and Formulations Available in the UK
Promethazine is available in different strengths and formulations in the UK. The exact product matters because the instructions are not always the same.
| Formulation | Strength | Typical use | Legal status |
|---|---|---|---|
| Phenergan tablets | 25mg | Allergy symptoms, travel sickness and short term insomnia in adults | Pharmacy medicine |
| Promethazine tablets | 10mg and 20mg | Promethazine products for allergy and other uses; availability varies | Depends on the product |
| Phenergan Elixir | 5mg per 5ml | Allergy symptoms, travel sickness and some age specific uses | Pharmacy medicine |
| Phenergan Injection | 25mg per ml | Clinical use only | Prescription only medicine |
NHS guidance confirms that promethazine tablets are available in 10mg, 20mg and 25mg strengths and that liquid promethazine contains 5mg in each 5ml. The Phenergan Elixir contains 5mg in each 5ml.
The injection is a different formulation and should not be used to work out an oral dose.
Choosing between tablets and elixir
| Consideration | 25mg tablets | Elixir 5mg/5ml |
|---|---|---|
| Dose precision | Fixed 25mg tablets | Can be measured in smaller amounts |
| Swallowing difficulty | May be a barrier | Can be easier to take |
| Ages 6 to 10 | Used for some indications | Recommended for travel sickness |
| Measuring required | No | Yes |
If you are taking the liquid, use the measuring syringe or spoon supplied with the medicine. Do not use an ordinary kitchen teaspoon because it may not measure the correct amount.
Phenergan Dosage for Sleep
Short term insomnia in adults is a licensed indication for Phenergan. The dose depends on age and formulation.
| Age group | Licensed night time dose for sleep | Source |
|---|---|---|
| Adults and children over 10 | 25mg or 50mg as a single night time dose | Phenergan 25mg tablets SmPC |
| Children 6 to 10 | 25mg as a single night time dose | Phenergan 25mg tablets SmPC |
| Children 6 to 10 (elixir) | 20mg or 25mg as a single night time dose | Phenergan Elixir SmPC |
| Children under 6 | Contraindicated | Phenergan SmPC |
The Phenergan 25mg tablet SmPC states that adults and children over 10 can take 25mg or 50mg as a single night time dose. The elixir SmPC gives 20mg or 25mg for children aged 6 to 10 and recommends the tablets for adults and children over 10 when these doses are needed.
Phenergan elixir dosage for sleep
Phenergan Elixir contains 5mg of promethazine in each 5ml. For children aged 6 to 10, the licensed sleep dose is 20mg or 25mg, which is 20ml or 25ml.
For adults and children over 10, the elixir can contain the same amount of promethazine, but the product information recommends using Phenergan tablets for the 25mg or 50mg night time dose.
Promethazine Dosage for Allergy Symptoms
Promethazine is licensed for the symptomatic treatment of allergic conditions affecting the upper respiratory tract and skin, including allergic rhinitis and urticaria.
The dose depends on the formulation.
| Age group | Formulation | Licensed allergy dose |
|---|---|---|
| Adults and children over 10 | 25mg tablets | 25mg as a single dose, increasing to a maximum of 25mg twice daily if needed |
| Adults and children over 10 | Elixir 5mg/5ml | 10mg twice daily, increasing to a maximum of 20mg three times daily if needed |
| Children 6 to 10 | 25mg tablets | 25mg as a single dose, maximum 25mg daily |
| Children 6 to 10 | Elixir 5mg/5ml | 10mg to 25mg as a single dose, or 5mg to 10mg twice daily, maximum 25mg daily |
NHS guidance gives the adult dose for hay fever or hives as 10mg twice a day up to 20mg three times a day, or 25mg once or twice a day. The exact instructions depend on the product you are taking.
Because promethazine can cause drowsiness, some people may find that taking a dose at night is more practical. Follow the instructions for your particular product rather than changing the timing yourself.
Phenergan Dosage for Travel Sickness, Nausea and Vertigo
| Situation | Age group | Licensed or NHS stated dose |
|---|---|---|
| Preventing travel sickness | Adults and over 10 | 25mg the night before, repeated after 6 to 8 hours if needed |
| Short journey | Adults and over 10 | Some promethazine products can be taken 1 to 2 hours before travelling |
| Treating travel sickness once it starts | Adults and over 10 | 25mg as soon as possible and 25mg the same evening, then 25mg the following evening if needed |
| Preventing travel sickness | Children 6 to 10 (elixir) | 10mg the night before, repeated after 6 to 8 hours if needed |
| Vertigo | Adults | 25mg a day, up to 25mg four times a day, depending on the advice and product instructions |
For Phenergan 25mg tablets, the product information gives 25mg the night before travel, with a repeat dose after 6 to 8 hours if needed. NHS guidance also notes that some promethazine products can be taken 1 to 2 hours before a short journey.
For children aged 6 to 10, the Phenergan Elixir SmPC gives 10mg the night before a journey, with a repeat dose after 6 to 8 hours if needed.
The NHS gives a wider dose range for vertigo, from 25mg a day up to 25mg four times a day. This is not a dose to choose for yourself. If you are taking promethazine for vertigo, follow the instructions given by your doctor or pharmacist.
Max Dose of Phenergan in 24 Hours
There is no single maximum promethazine dose that applies to every situation. The limit depends on why you are taking it, your age and the formulation.
| Indication | Stated 24 hour maximum | Notes |
|---|---|---|
| Short term insomnia | 50mg | A single night time dose |
| Allergy, 25mg tablets | 50mg | 25mg twice daily |
| Allergy, elixir | 60mg | 20mg three times daily |
| Allergy, children 6 to 10 | 25mg | Maximum daily dose |
| Vertigo | Up to 100mg | NHS stated range; follow medical advice |
For someone asking about the maximum dose for sleep, the licensed adult dose is 50mg as a single night time dose. That does not mean 50mg is appropriate for everyone, or that increasing the dose is a good way to get a stronger effect.
Taking more promethazine than recommended can be dangerous. Overdose can cause severe drowsiness, unconsciousness, breathing problems, seizures, abnormal heart rhythms and other serious effects. Children can also develop agitation, hallucinations or uncontrolled movements.
If you take more than the recommended dose, seek urgent medical advice even if you feel well. NHS guidance advises contacting 111 after taking too much promethazine, and calling 999 or going to A&E if there are serious symptoms such as breathing problems, a seizure, unconsciousness or a very fast or irregular heartbeat.
Phenergan Dose Per kg: Why UK Dosing Is Age Banded
Weight based dosing is common for some medicines in children, so looking for a Phenergan dose per kg is understandable. For oral Phenergan in the UK, however, the licensed dosing information is based on age and the reason for treatment rather than a published mg per kg formula.
This means there is no general UK mg/kg dose for oral Phenergan that parents should calculate at home. Do not use a weight based formula from another website to work out a child's dose.
If you are looking for information about weight loss treatment or taking other medicines at the same time, speak to a pharmacist or prescriber about how promethazine fits into your treatment.
How Long Can You Take Phenergan For?
The Phenergan patient information leaflet says not to take the medicine for longer than 7 days. If your symptoms get worse or do not improve after 7 days, you should speak to a doctor or pharmacist. NHS guidance also recommends using promethazine for only a short time unless a doctor advises otherwise.
This is particularly important if you are using Phenergan for sleep. If you keep having trouble sleeping, taking the medicine for longer does not address the reason behind the problem. A doctor can help look at possible causes and other treatment options.
If you have been taking promethazine for a long time, do not stop it suddenly without medical advice. NHS guidance says that some people can experience symptoms such as dizziness, sweating, nausea, a racing heart and difficulty sleeping after stopping long term use suddenly.
Who Should Not Take Promethazine
Do not take oral Phenergan if:
- You have had an allergic reaction to promethazine, another phenothiazine or an ingredient in the product.
- You are in a coma or have central nervous system depression.
- The person taking it is under 6 years of age.
- You have taken a monoamine oxidase inhibitor (MAOI) within the previous 14 days.
Speak to a doctor or pharmacist before taking it if you have:
- Liver or kidney problems, Parkinson's disease, an underactive thyroid, heart failure, myasthenia gravis or an enlarged prostate.
- A history of narrow angle glaucoma.
- Epilepsy or another condition that causes seizures.
- Asthma, bronchitis or bronchiectasis.
- Problems emptying your bladder or an obstruction affecting your digestive system.
- A heart rhythm problem or take medicines that can affect the QT interval.
- Other medicines that cause drowsiness or have anticholinergic effects.
Older adults can be more sensitive to the anticholinergic effects of promethazine and may be more likely to experience confusion. Tell your pharmacist or doctor about all the medicines you take, including medicines bought without a prescription and herbal products.
If you are having an allergy skin test, tell the healthcare professional that you take promethazine. Antihistamines can affect the results of some allergy tests.
Side Effects, Alcohol and Driving
Drowsiness or sleepiness is a very common effect of promethazine. Other possible effects include dizziness, headache, blurred vision, dry mouth and constipation. Some people can also experience difficulty passing urine or movement related side effects.
Promethazine can also make some people more sensitive to sunlight, so avoid strong sunlight and sunbeds during treatment and for a short time afterwards.
Alcohol should be avoided. Alcohol can increase the sedating effects of promethazine. Other medicines that cause drowsiness can also increase sedation, so check with a pharmacist before taking them together.
Do not drive, cycle or operate machinery if you feel sleepy, dizzy, have blurred vision or feel unable to concentrate properly.
Buying Phenergan in the UK: Legal Status, Cost and What to Check
Phenergan 25mg tablets and Phenergan Elixir are pharmacy medicines in the UK. This means they are supplied through a pharmacy and are subject to a pharmacist's suitability check.
If you are buying promethazine online, check that you are using a properly registered UK pharmacy. You should also be able to find clear information about who is supplying the medicine and how the clinical assessment is carried out.
Phenergan prices at EveryDayMeds
| Product | Pack size | Price | Approximate cost per dose |
|---|---|---|---|
| Phenergan 25mg tablets (promethazine hydrochloride) | 56 tablets | £14.99 | About £0.27 per 25mg tablet |
| Phenergan Elixir 5mg/5ml | 100ml | £14.49 | About £3.62 per 25mg dose |
These are the prices supplied for this page and should be checked against the live product listings before publication or ordering. Promotional offers, delivery charges or other fees may change the final price.
Questions to ask before buying promethazine online
- Is the seller a registered pharmacy? Check that the pharmacy is registered with the General Pharmaceutical Council where applicable.
- Is there a clinical check? The pharmacy should check whether the medicine is suitable before supplying it.
- Is the price the total price? Check whether delivery, consultation or other charges are added at checkout.
- Is the medicine genuine and in date? A legitimate pharmacy should provide information about the medicine it supplies and how it is sourced.
- Can you contact the pharmacy? Clear contact details make it easier to ask questions before ordering.
Things to Know Before Your First Dose
- Take Phenergan exactly as directed for the reason you are using it. For sleep, the licensed adult dose is taken as a single dose at night.
- Make sure you have enough time to sleep before taking it. You may still feel drowsy the following morning.
- Swallow tablets whole with water. Do not chew them.
- Measure the elixir using the supplied oral syringe or medicine spoon, not a kitchen teaspoon.
- Do not drink alcohol while taking Phenergan.
- If you forget a dose for sleep or sedation, do not take two doses together. For travel sickness, follow the missed dose instructions for your particular product.
- Do not increase the dose yourself if you feel that the medicine is too weak or does not seem to be working. Ask a pharmacist or doctor instead.
- Do not take Phenergan for longer than 7 days without speaking to a doctor or pharmacist. If your sleep has not improved or your symptoms are continuing, it is worth finding out why rather than simply continuing the medicine.
Medical Disclaimer
This Phenergan dosage guide was compiled by the EveryDayMeds editorial team using UK product information for Phenergan 25mg tablets, Phenergan Elixir and Phenergan Injection, approved patient information leaflets, NHS medicines guidance and insomnia guidance, and NICE Technology Appraisal TA77. It explains licensed UK dosing for information only and is not a recommendation to take promethazine at any particular dose.
The right treatment and dose depend on factors such as your age, the reason you are taking the medicine, your other medicines and your health. Your pharmacist, prescriber or other qualified healthcare professional can assess whether promethazine is suitable for you and explain how to use it.
If you are unsure about a dose, have taken more than recommended or are experiencing troublesome side effects, speak to a pharmacist, doctor or appropriate medical service for advice.
