Promethazine (Phenergan) is a licensed antihistamine used for allergic conditions such as hay fever and hives. It is also used for sickness, including motion sickness, and is known to cause drowsiness. However, being allergic to promethazine itself is a different matter. Anyone who has previously had an allergic reaction to promethazine should not take it unless a healthcare professional advises otherwise. Signs of an allergic reaction can include a rash, swelling, or difficulty breathing and require prompt medical attention.
For UK adults considering options for allergy symptoms, this guide explains what promethazine is used for, how it works, the usual dosing information, the difference between a runny nose and nasal congestion, and how it compares with newer, less sedating antihistamines.
Key things to know and side effects of promethazine
- Promethazine is a first generation, sedating antihistamine that is used for allergic conditions such as hay fever and hives.
- It may help reduce a runny nose and other allergy symptoms, but it does not work as a decongestant for a blocked nose.
- For adults and children aged over 10 years, NHS guidance states that the dose for hay fever or hives can range from 10mg twice a day to 20mg three times a day, or 25mg once or twice a day, depending on the product and individual circumstances.
- Being allergic to promethazine itself is different from using promethazine to treat an allergy. People with a known hypersensitivity to promethazine should not take it.
Is Promethazine an Antihistamine?
Yes. Promethazine is a first generation antihistamine. It works by blocking histamine, a substance involved in allergic reactions. This can help relieve symptoms such as sneezing, a runny nose, itching and watery eyes.
Unlike some newer antihistamines, promethazine can make you feel sleepy because it has a stronger effect on the brain. This is why it is classed as a sedating or drowsy antihistamine.
What It Is Genuinely Licensed For, Including Motion Sickness
Promethazine is licensed for allergic conditions affecting the upper respiratory tract and skin, including allergic rhinitis and urticaria, also known as hives. UK product information also lists its use as an antiemetic, meaning it can be used to help prevent or treat nausea and vomiting, including motion sickness.
Promethazine also has licensed uses related to short term insomnia in adults for certain products. This means that its drowsiness is a recognised effect of the medicine, rather than simply an unexpected side effect. However, that does not mean it is the best choice for everyone with allergies or sleep problems.
Congestion vs a Runny Nose: An Important Distinction
A runny nose and a blocked nose are not quite the same allergy symptom. Promethazine may help with a runny nose because antihistamines can reduce some of the symptoms caused by histamine during an allergic reaction.
A blocked or stuffy nose is different. Nasal congestion is linked to swelling inside the nasal passages, and promethazine is not a decongestant. If nasal blockage is your main problem, a pharmacist can advise whether another treatment, such as a suitable nasal spray or decongestant, may be more appropriate for you.
Many people with hay fever have several symptoms at the same time, including sneezing, an itchy or runny nose, watery eyes and nasal congestion. This can make it difficult to tell which symptom a particular medicine is helping. Promethazine may help with some allergy symptoms, but it should not be expected to relieve every symptom in the same way.
Dosing for Allergic Conditions
According to NHS guidance on how and when to take promethazine, for hay fever or hives, the dose for adults and children aged over 10 years can range from 10mg twice a day to 20mg three times a day, or 25mg once or twice a day. The appropriate dose depends on the reason for treatment and the specific promethazine product being used. Always follow the instructions supplied with your medicine or advice from your doctor or pharmacist.
Dosing for younger children is different and depends on their age and the product. Some promethazine products have specific age restrictions, so children should not be given an adult dose unless a healthcare professional has advised it.
Because promethazine can cause drowsiness, some people may prefer to take it in the evening if their allergy symptoms are particularly troublesome at night. However, drowsiness can also be a drawback, especially during the daytime. If you need to stay alert for work, driving or other activities, a less sedating antihistamine may be more suitable.
Do not drive, cycle or operate machinery if promethazine makes you sleepy, dizzy or affects your concentration. Alcohol can also increase the risk of side effects and should be avoided while taking promethazine.
Am I Allergic to Promethazine?
This is different from asking what promethazine treats. Here, the question is whether you may be having an allergic reaction to the medicine itself. People with a known hypersensitivity to promethazine or other phenothiazines should not take it, as this is listed as a contraindication. Signs of an allergic reaction can include a skin rash, itching, swelling of the face or throat, or difficulty breathing. These symptoms need prompt medical attention. If you are having difficulty breathing or experiencing severe swelling, seek emergency medical help. Allergic reactions can happen soon after taking a medicine, although some reactions may develop later.
This is different from common side effects such as drowsiness or dry mouth. These side effects are not usually signs of an allergic reaction, although they can still be troublesome for some people.
For more information about who can and cannot take promethazine, including other contraindications, see our promethazine safety guide.
Comparing Sedating and Non Sedating Antihistamines
Newer antihistamines such as cetirizine, loratadine and fexofenadine generally enter the brain less readily than older antihistamines such as promethazine. As a result, they are less likely to cause drowsiness for most people, although some people can still feel sleepy when taking them.
Promethazine can cause drowsiness and dizziness. For some people, this may be a disadvantage, particularly if they need to stay alert during the day. If allergy symptoms are worse at night, the sedating effect may also be something a healthcare professional considers when deciding whether promethazine is appropriate. This does not mean that promethazine is automatically better for night time symptoms or that a non sedating antihistamine is always the better choice. The most suitable option can depend on your symptoms, when they occur and how you respond to the medicine.
Promethazine can also cause side effects such as dry mouth and blurred vision. Its anticholinergic effects can also reduce secretions. Newer antihistamines generally have fewer of these effects, although side effects can vary between medicines and between individuals.
The choice is therefore not simply about which antihistamine is stronger. It is also about the type of symptoms you have and whether drowsiness or other side effects could affect your day. Avoid drinking alcohol while taking promethazine because alcohol can increase drowsiness. Other medicines that cause drowsiness can also increase this effect.
A Quick Way to Decide and Avoid Double or Extra Doses
If your main symptoms are sneezing, itchy or watery eyes, and a runny nose, promethazine is a licensed option for allergic conditions such as hay fever. If these symptoms are particularly troublesome at night, speak to a pharmacist or doctor about whether promethazine is suitable for you.
If your main symptom is a blocked or stuffy nose, promethazine may not address the congestion itself because it is an antihistamine rather than a decongestant. A pharmacist can advise whether another treatment may be more appropriate.
If you need to remain alert for work, driving or other activities, a less sedating antihistamine may be worth discussing with a pharmacist. Do not drive or operate machinery if promethazine makes you sleepy, dizzy or affects your concentration.
Most importantly, do not take more than the recommended dose or take an extra dose because you feel that the medicine is not working quickly enough. If you are unsure about when to take your next dose, speak to a pharmacist or check the instructions supplied with your medicine.
Available Treatments
| Treatment | Price |
|---|---|
| Phenergan 25mg (Promethazine Hydrochloride) - 56 Tablets | £14.99 |
| Phenergan Elixir 5mg/5ml Oral Solution - 100ml | £14.49 |
Prices update live and may change.
Sources
- NHS: How and when to take promethazine (nhs.uk/medicines/promethazine/how-and-when-to-take-promethazine)
- NHS: Who can and cannot take promethazine (nhs.uk/medicines/promethazine/who-can-and-cannot-take-promethazine)
Medical Disclaimer
This page provides general information about promethazine for allergic rhinitis and related conditions. It is not a substitute for personalised medical advice, diagnosis or treatment.
If you are unsure whether promethazine is suitable for your symptoms, speak to your doctor, pharmacist or GP. If you experience signs of an allergic reaction to promethazine, such as swelling or difficulty breathing, seek prompt medical attention.
