Phenergan and cetirizine are both antihistamines, but they have some important differences. Phenergan contains promethazine, a sedating antihistamine that can make you sleepy. Cetirizine is classed as a non drowsy antihistamine, although some people can still feel sleepy after taking it. Phenergan also has uses beyond allergy, while cetirizine is mainly used for allergy symptoms and hives.
For routine hay fever and hives, a non drowsy antihistamine such as cetirizine is often preferred, particularly if you need to stay alert during the day. That does not mean Phenergan cannot be useful. Its sedating effect may be helpful in some situations, such as when allergy symptoms are affecting sleep.
This guide explains where each medicine fits, whether they can be taken together, and how some of the brand names you may see in the UK and abroad relate to these medicines.
Key Things to Know
- Phenergan is a brand of promethazine hydrochloride, a sedating antihistamine. Cetirizine is classed as a non drowsy antihistamine, although it can still cause sleepiness in some people.
- NICE and NHS guidance generally favours a non sedating antihistamine for routine allergic rhinitis and urticaria.
- Promethazine can cause drowsiness and other side effects such as dry mouth, blurred vision and dizziness. Cetirizine can also cause sleepiness, although it is less likely to do so than sedating antihistamines.
- Promethazine is used for allergies and can also be used for motion sickness and nausea. Some Phenergan products have other licensed uses. Cetirizine is mainly used for allergies and hives.
- Taking both together is not something you should do without advice from a pharmacist or doctor, as combining antihistamines can increase side effects.
- Zyrtec is a brand of cetirizine used outside the UK, while Allergex is a brand of chlorphenamine used in South Africa. Checking the active ingredient is the best way to know which medicine you are comparing.
What Is Phenergan, and What Does Promethazine Do?
Phenergan is a UK brand of promethazine hydrochloride. Promethazine is a sedating antihistamine that belongs to the phenothiazine group.
As well as blocking histamine H1 receptors, promethazine can affect other chemical signals in the body. This helps explain why it can cause drowsiness and why it has uses beyond allergy symptoms, including motion sickness and nausea.
Depending on the specific product, promethazine can be used for allergic conditions such as hay fever and hives, motion sickness and other symptoms. Some Phenergan products also have specific licensed uses that are not shared by cetirizine.
Promethazine may also be listed as an adjunct in the emergency treatment of anaphylaxis. An adjunct means it may be used alongside emergency treatment. It is not a replacement for adrenaline or emergency medical care. If someone has symptoms of anaphylaxis, call 999 and follow emergency advice.
What Is Cetirizine?
Cetirizine hydrochloride is a second generation antihistamine. It works by blocking histamine H1 receptors and is much less likely to cause drowsiness than sedating antihistamines. However, some people still feel sleepy or tired after taking it.
Cetirizine is used for hay fever, other allergies and hives. Adults usually take it once a day, although the dose can be different for children and people with kidney problems.
In the UK, cetirizine is available as a generic medicine and under brand names including Zirtek and Piriteze. Some Benadryl products also contain cetirizine, so checking the active ingredient on the packet is useful.
So, is cetirizine like promethazine? They are similar because both are antihistamines that block H1 receptors. The main difference is how they affect you and what they are normally used for.
Difference Between Promethazine and Cetirizine
However the search is phrased, whether you are looking for promethazine vs cetirizine, promethazine hydrochloride vs cetirizine or Phenergan vs cetirizine, these are the practical differences to know.
| Feature | Phenergan (promethazine) | Cetirizine |
|---|---|---|
| Antihistamine generation | First | Second |
| Chemical group | Phenothiazine | Piperazine derivative |
| Main action | Blocks histamine H1 receptors and can affect other receptors | Mainly blocks histamine H1 receptors |
| Sedation | Can cause significant drowsiness | Less likely to cause drowsiness, but sleepiness can occur |
| Duration | Drowsiness can last for several hours | Usually taken once daily |
| Dosing pattern | Depends on why it is being used | Usually once daily for adults |
| Anticholinergic effects | Can cause dry mouth, blurred vision and other effects | Less likely to cause these effects |
| Main licensed uses | Allergy, motion sickness and other product specific uses | Allergy symptoms and hives |
| Minimum age | Depends on the product; Phenergan 25mg tablets are not for under 6s | Depends on the product and formulation |
| Legal category | Pharmacy medicine for some UK products | Depends on the product and pack |
The duration of promethazine can vary depending on the person, dose and reason for taking it. NHS information says drowsiness usually wears off within around 12 hours. This is different from saying that the medicine always lasts for exactly 12 hours.
Cetirizine is usually taken once a day. This does not mean everyone will experience exactly 24 hours of symptom relief, so follow the instructions for your particular product.
Which One Does UK Guidance Recommend?
For routine allergy symptoms, a non drowsy antihistamine is often preferred. NICE guidance recommends a non sedating antihistamine for allergic rhinitis, while NHS guidance describes cetirizine as a non drowsy antihistamine that is less likely to make you sleepy than some other antihistamines.
This does not mean promethazine does not work for allergies. It can be used for allergic conditions, but its sedating effects can make it less suitable when you need to stay alert.
If your main problem is a blocked or stuffy nose, changing from one antihistamine tablet to another may not be the most useful approach. A steroid nasal spray may be recommended for some people with allergic rhinitis, particularly when nasal symptoms are more troublesome.
How the Common Antihistamines Compare
| Medicine | Generation | Sedating | Mainly used for |
|---|---|---|---|
| Cetirizine | Second | Less likely, but sleepiness can occur | Hay fever, allergy, hives |
| Loratadine | Second | Less likely, but sleepiness can occur | Hay fever, allergy, hives |
| Fexofenadine | Second | Less likely to cause drowsiness | Hay fever, allergy, hives |
| Acrivastine | Second | Less likely to cause drowsiness | Hay fever and allergies |
| Chlorphenamine | First | Yes | Allergy and allergic reactions |
| Promethazine | First | Yes | Allergy, motion sickness and other uses |
| Cinnarizine | First | Yes | Motion sickness and vertigo |
Fexofenadine, loratadine, cetirizine and acrivastine are generally less likely to cause drowsiness than older sedating antihistamines, although individual reactions vary.
There are also practical differences between them. For example, NHS advice says fexofenadine should be taken with water because some fruit juices can reduce how much of the medicine is absorbed.
The Brand Name Problem
The same brand name can refer to different medicines in different countries. This is one of the main reasons online comparisons can become confusing.
| Brand you may have seen | Where it is sold | What it contains |
|---|---|---|
| Zyrtec | United States and many others | Cetirizine |
| Benadryl | United Kingdom | Acrivastine in Benadryl Allergy Relief |
| Benadryl | United States | Diphenhydramine in some products |
| Allergex | South Africa | Chlorphenamine |
| Polaramine | Australia and some other markets | Dexchlorpheniramine in relevant products |
| Avil | India and some other markets | Pheniramine in relevant products |
| Piriton | United Kingdom | Chlorphenamine |
The Benadryl difference is particularly important. UK Benadryl Allergy Relief contains acrivastine, while some US Benadryl products contain diphenhydramine.
The safest habit is simple: check the active ingredient and strength on the packet rather than relying only on the brand name.
Side Effects: What the Product Information Actually Lists
Promethazine can cause drowsiness, which is one of its most important practical side effects. Other possible effects include dry mouth, constipation, blurred vision, dizziness and difficulty concentrating. Not everyone will experience these effects.
Cetirizine can also cause sleepiness or tiredness. Other possible side effects include headache, dry mouth, nausea, dizziness and diarrhoea.
How strongly you react can vary from person to person. If cetirizine makes you sleepy, speak to a pharmacist about whether another non drowsy antihistamine may be more suitable.
Safety, Driving and Who Should Avoid Promethazine
Promethazine can make you sleepy, dizzy or less able to concentrate. If you feel affected, do not drive, cycle or use machinery. Alcohol can also increase the sedating effects of promethazine.
Promethazine has some important precautions:
- It should not be taken with an MAOI or within 14 days of stopping one. If you take an antidepressant or another medicine that may be an MAOI, check with a pharmacist or doctor before taking promethazine.
- The age restriction depends on the product. Phenergan 25mg tablets are not for children under 6 years old. Other promethazine products can have different age restrictions, so check the specific product information.
- It may not be suitable for people with certain conditions, including epilepsy, asthma or other breathing problems, liver or kidney problems, Parkinson's disease, heart problems, an enlarged prostate or narrow angle glaucoma.
- Phenergan 25mg tablets should not be used for longer than 7 days without medical advice. Other promethazine products may have different instructions.
- Promethazine can interact with other medicines that cause drowsiness. Check with a pharmacist before taking it with sleeping tablets, some pain medicines or other medicines that make you sleepy.
Cetirizine is generally less sedating, but it can still cause sleepiness. People with kidney problems may also need a lower dose. Check the product instructions or ask a pharmacist if you are unsure.
Which Suits Which Situation
| What you need | A possible starting point |
|---|---|
| Hay fever or ongoing allergy during the day | Cetirizine or another non drowsy antihistamine |
| Hives and itching | A non drowsy antihistamine may be suitable |
| A blocked nose as the main symptom | A steroid nasal spray may be more suitable |
| Allergy symptoms disturbing sleep | A sedating antihistamine may sometimes be recommended at night |
| Motion sickness | Promethazine or cinnarizine, depending on the individual situation |
| Short term sleep difficulty | Sleep habits first, followed by advice on whether medicine is appropriate |
| Driving or safety critical work | A less sedating option may be preferable |
If your symptoms are not improving, keep coming back or need treatment for a long time, speak to a pharmacist or GP rather than continually changing medicines yourself.
Can You Take Cetirizine and Promethazine Together?
It is best to ask a pharmacist or doctor before taking cetirizine and promethazine together.
Both are antihistamines, and combining them can increase the chance of side effects such as drowsiness. Promethazine can also cause anticholinergic effects such as dry mouth and blurred vision.
There are situations where a doctor may recommend more than one antihistamine, such as using a non drowsy antihistamine during the day and a sedating antihistamine at night for a specific problem. That should be based on your symptoms and medical history rather than something you decide to do yourself.
The same applies to Zyrtec and Phenergan because Zyrtec contains cetirizine.
Cost and Formulations
Price may be one factor when choosing a medicine, but the more important question is whether the medicine is suitable for your symptoms and whether you need a sedating or non drowsy option.
| Product | Pack | Price |
|---|---|---|
| Phenergan 25mg tablets | 56 tablets | £14.99 |
| Phenergan Elixir 5mg/5ml | 100ml oral solution | £14.49 |
Prices were correct at the time of writing, and the live product pages take precedence.
Cetirizine is widely available from pharmacies and shops in the UK. The price can vary depending on the brand, pack size and retailer.
The Phenergan Elixir may be useful for people who have difficulty swallowing tablets. Phenergan 25mg tablets are another available formulation. The most suitable product depends on factors such as age, symptoms and why the medicine is being used.
Phenergan is available as a pharmacy medicine in the UK. This means a pharmacist is involved in its supply, which also gives you an opportunity to ask whether it is suitable for you and whether it can be taken with your other medicines.
Medical Disclaimer
This page provides general information about promethazine, Phenergan and cetirizine in the UK. It is not medical advice, a diagnosis or a substitute for advice from a pharmacist, GP or another qualified healthcare professional who knows your medical history.
No dose is recommended on this page. Always follow the instructions on your medicine and the patient information leaflet, and do not exceed the stated dose. If you are thinking about taking two antihistamines together, speak to a pharmacist or doctor first rather than combining them yourself.
Phenergan 25mg tablets should not be used for longer than 7 days without medical advice. Other promethazine products may have different instructions, so check the information supplied with your medicine.
Anaphylaxis is a medical emergency. If someone has symptoms of anaphylaxis, call 999 and follow emergency advice. Adrenaline is the main emergency treatment, and an antihistamine should not be used instead of emergency medical care.
