If you are comparing Phenergan and Benadryl in the UK, there is one important thing to know first: UK Benadryl is not the same medicine as US Benadryl, and it does not contain diphenhydramine. This matters because you could otherwise end up comparing two very different antihistamines.
This guide explains what each product contains and how promethazine, diphenhydramine and UK Benadryl compare for sleep and allergies.
The Confusion at the Heart of This Question
The name "Benadryl" refers to different medicines in different countries. This is why searches for "Phenergan vs Benadryl" can be confusing.
Here is what the different products contain:
| Product | What it contains | Sedating? |
|---|---|---|
| Phenergan | Promethazine | Yes, it can cause drowsiness |
| Benadryl Allergy Relief (UK) | Acrivastine | Usually considered non drowsy |
| Benadryl One a Day (UK) | Cetirizine | Less likely to cause drowsiness |
| Benadryl (US) | Diphenhydramine | Yes, it can cause drowsiness |
| Nytol Original (UK) | Diphenhydramine | Yes, it can cause drowsiness |
So, the diphenhydramine that people in the US may know as Benadryl is a different product from the Benadryl Allergy Relief sold in the UK. In the UK, diphenhydramine is found in products such as Nytol Original.
So Which Comparison Do You Actually Mean?
Once you know what the names contain, there are two different comparisons:
- Phenergan vs UK Benadryl means promethazine vs acrivastine if you are referring to Benadryl Allergy Relief. These are different types of antihistamine. Promethazine can make you drowsy, while acrivastine is generally considered a non drowsy antihistamine.
- Promethazine vs diphenhydramine is the comparison to make if you mean the US version of Benadryl or a UK product such as Nytol Original. Both are drowsy antihistamines.
The rest of this guide looks at both comparisons.
Phenergan vs Diphenhydramine for Sleep
This is the comparison many people actually mean when they search for Phenergan vs Benadryl.
Promethazine and diphenhydramine are both drowsy, first generation antihistamines. Their sedating effects are one reason they can be used for short term sleep problems. However, feeling sleepy does not mean that either medicine is suitable for everyone or for long term use.
Promethazine can cause drowsiness that continues into the following day. Some UK guidance notes that its effects can last for several hours, so you may still feel sleepy or less alert after taking it at night.
Diphenhydramine is also used as a short term aid for temporary sleep disturbance. UK product information states that it should not be used continuously for more than 2 weeks without speaking to a doctor.
There is no simple answer to which one is "better". The right option depends on the reason you need it, your other medicines, your health and how you respond to the medicine. If sleep problems continue, speak to a doctor rather than continuing to use a sedating antihistamine.
Phenergan vs Benadryl for Allergies
For allergies, the answer depends on which Benadryl product you mean.
UK Benadryl Allergy Relief contains acrivastine, which is a non drowsy antihistamine. It is used to relieve symptoms of allergic rhinitis, including hay fever, and chronic idiopathic urticaria.
Benadryl One a Day contains cetirizine, another antihistamine that is less likely to cause drowsiness than medicines such as promethazine, although some people can still feel sleepy after taking it.
Promethazine can also be used for allergy symptoms, but it is a drowsy antihistamine. This can make it less convenient during the day if you need to stay alert. NHS guidance notes that many people prefer non drowsy antihistamines because they are less likely to interfere with their normal routine.
So, if you are looking for daytime hay fever relief, a non drowsy antihistamine may be a more suitable option for some people. A pharmacist can help you choose one based on your symptoms and other medicines.
Is Promethazine Stronger Than Diphenhydramine or Benadryl?
"Stronger" is not a very useful way to compare these medicines.
Promethazine and diphenhydramine are different medicines. Both can cause drowsiness, but they can affect people differently. One may make you feel more sleepy than the other, but that does not mean it is simply "stronger".
The same applies to Benadryl. If you mean UK Benadryl Allergy Relief, it contains acrivastine, so it is not the same medicine as diphenhydramine.
It is more helpful to look at what you need the medicine for, how likely it is to make you drowsy, how long you need the effect to last and whether it is suitable for you.
Can You Take Phenergan and Benadryl Together?
It is generally best not to combine antihistamines unless a doctor or pharmacist has advised you to do so.
If the Benadryl product contains a drowsy antihistamine such as diphenhydramine, taking it with promethazine can increase drowsiness and other side effects. These can include dry mouth, blurred vision and difficulty passing urine.
If your Benadryl product contains a non drowsy antihistamine such as acrivastine, you should still check with a pharmacist or doctor before taking it with promethazine. Taking two antihistamines is not usually necessary unless you have been specifically advised to do so.
This is especially important if you take other medicines or medicines that can make you sleepy. Alcohol should also be avoided with promethazine because it can increase drowsiness and can make it harder to wake or breathe normally.
If you have accidentally taken two antihistamines, do not take any more until you have checked what you have taken and spoken to a pharmacist, doctor or NHS 111 if needed. Get urgent medical help if you have severe drowsiness, difficulty breathing, loss of consciousness, severe confusion or other worrying symptoms.
Safety, Age Limits and Who Should Avoid Them
The safety information can vary depending on the exact product, strength and formulation, so always check the leaflet that comes with your medicine.
- Phenergan (promethazine) should not be used in children under 6 years of age. It should also be avoided in people who have taken monoamine oxidase inhibitors (MAOIs) within the previous 14 days.
- Diphenhydramine sleep medicines are not intended for children under 16 years of age and should not be used continuously for more than 2 weeks without speaking to a doctor.
- Both medicines can cause drowsiness. This can affect your ability to drive or operate machinery. Do not drive if you feel sleepy, dizzy or unable to concentrate.
- Older adults may be more likely to experience side effects from sedating antihistamines, including confusion and problems with coordination.
- Speak to a doctor or pharmacist before using these medicines if you have conditions such as asthma or other breathing problems, glaucoma, an enlarged prostate, difficulty passing urine, epilepsy, or liver or kidney problems.
- Tell your doctor or pharmacist about any other medicines, including other antihistamines, medicines that cause drowsiness and medicines you buy without a prescription.
