The short answer: Sominex contains promethazine, a longer-acting sedating antihistamine that may be suitable for people who wake during the night, while Nytol uses diphenhydramine and Kalms uses herbal valerian root. They work differently and are intended for short-term use rather than ongoing insomnia.
Walk down the sleep aid aisle in any UK pharmacy and you'll see Sominex sitting next to Nytol, Kalms and a range of herbal sleep products - all designed to support better sleep, but working in different ways. Choosing an option without understanding the differences may mean you select a product that doesn't match your particular sleep problem. Here's how the main OTC options compare and what to consider when choosing between them.
How Does Sominex Work?
Sominex contains promethazine hydrochloride, a sedating antihistamine that can cause drowsiness by blocking histamine receptors involved in wakefulness.
Sominex is taken as one tablet at bedtime, or up to an hour after going to bed if you haven't fallen asleep. It typically starts to take effect within around 20–30 minutes.
It is licensed for adults and adolescents aged 16 and over for temporary sleep difficulties associated with factors such as stress, jet lag or a disrupted routine. It is not intended as a long-term treatment for insomnia.
Sominex should not be used for more than 7 consecutive nights.
Sominex vs Nytol vs Kalms: Key Differences at a Glance
These are widely available UK sleep-aid options, but they contain different active ingredients and may be more appropriate for different types of sleep difficulties.
| Feature | Sominex | Nytol One-A-Night | Kalms Night |
|---|---|---|---|
| Active Ingredient | Promethazine hydrochloride 20mg | Diphenhydramine 50mg | Valerian root extract |
| How It Works | Sedating antihistamine that promotes drowsiness | Sedating antihistamine that promotes drowsiness | Herbal preparation traditionally used to support relaxation and sleep |
| Time to Work | Around 20–30 minutes | Around 20–30 minutes | May vary between individuals |
| Typical Use | Temporary sleep difficulties | Temporary difficulty falling asleep | Mild sleep difficulties and relaxation support |
| Maximum Recommended Use | 7 consecutive nights | Follow the specific product instructions | Follow the specific product instructions |
| Age | 16 years and over | 16 years and over, depending on the specific product | Check the individual product packaging |
Which Sleep Aid Should You Choose?
The most appropriate option depends on the type and cause of your sleep difficulty. Rather than choosing based solely on which product is described as "stronger", consider the nature of your symptoms and speak to a pharmacist if you're unsure.
- Difficulty falling asleep: An antihistamine sleep aid such as Nytol may be used for short-term sleep difficulties, where appropriate.
- Temporary sleep disruption: Sominex may be suitable for short-term sleep difficulties associated with factors such as stress, jet lag or a disrupted routine.
- Mild sleep difficulties: A valerian-based product such as Kalms Night may be considered by some adults.
- Sleep problems occurring regularly: If you're having difficulty sleeping most nights for several weeks, speak to a GP rather than relying on OTC sleep aids.
It's important to remember that OTC sleep aids are intended for short-term use. They are not designed to treat the underlying causes of persistent insomnia.
Safety, Side Effects and How Long Can You Use Them?
Sominex and other sedating antihistamine sleep aids can cause next-day drowsiness, dry mouth, dizziness and reduced alertness. Do not drive, cycle or operate machinery if you feel drowsy or impaired after taking a sleep aid.
Do not combine sedating antihistamine sleep aids with alcohol or other medicines that cause drowsiness unless a healthcare professional has advised you that it is safe.
Sominex specifically should not be used for more than 7 consecutive nights. It should also not be combined with other medicines that cause drowsiness, including some strong painkillers such as codeine or morphine, or certain medicines used for depression or seizures, without first checking with a pharmacist or doctor.
If your sleep problems continue despite short-term use, speak to a healthcare professional rather than continuing to take sleep aids indefinitely.
Frequently Asked Questions
Is Sominex the same as Nytol?
Is Sominex addictive?
How long does Sominex take to work?
Can I take Sominex every night?
What is the strongest over-the-counter sleeping pill in the UK?
There is no single "best" over-the-counter sleep aid. The appropriate choice depends on the nature of your sleep difficulty, your health and any other medicines you take.
Sominex contains promethazine, a sedating antihistamine intended for short-term sleep difficulties. Nytol contains diphenhydramine, another sedating antihistamine, while Kalms Night contains valerian and offers a herbal approach to temporary sleep difficulties.
All of these products are intended for short-term use. If you regularly struggle to sleep or your sleep problems persist, it's better to speak to a GP or pharmacist to identify the underlying cause rather than relying on OTC sleep aids.
Not sure which sleep aid is appropriate for you? Speak to your pharmacist before choosing an OTC sleep product.
Medical Disclaimer: This article is for general information only and is not a substitute for advice from a pharmacist or doctor. Always read the patient information leaflet and product packaging before use. Do not combine sleep aids with alcohol or other medicines that cause drowsiness unless advised by a healthcare professional. If sleep problems persist, speak to a GP or other qualified healthcare professional.