Sominex Anti-Histamine Sleep Aid Review

sominex sleep aid

Sominex is an over the counter sleep aid that uses an anti-histamine as the active ingredient.

In this review, I’ll describe my personal experience of taking it, and the side effects I had. Please remember that this is just one person’s experience, and it might work differently for you.

So further in the article, you’ll also find important guidance and safety advice based on the patient leaflet and current medical advice.

The different types of Sominex

It’s important to first understand that there are several different versions of Sominex.

In the UK, the main ingredient is promethazine. However, in the US and Canada, it’s diphenhydramine. They are both anti-histamines, but they aren’t the same.

Note that this review is based on the UK version only.

Secondly, don’t confuse it with the herbal sleep aid in the UK, which is completely different. For more about that one, you can see my Sominex Herbal review.

Finally, in India the name Sominex is used for a heartburn and indigestion drug, not a sleep aid at all.

My experience

With the unbearable mugginess of a rare British heatwave turning my bedroom into a nighttime sauna, I’d had several bad night’s sleep in a row.

So I took my first Sominex pill on a Sunday night, an hour before bedtime, in the hope it would put a stop to the sweaty sleeplessness.

I went to bed shortly after taking it to read a book, keen to keep at eye out for any noticeable sedative effect.

After about 45 minutes I remember starting to feel quite drowsy. I put my book down, turned off the light, and I’m pretty sure I was asleep in around 5 to 10 minutes.

Sleeping through the night

I only woke once in the night, which was markedly different from the previous few nights. I remember feeling very out of it though, had a sip of water and quickly fell asleep again.

I then woke up around 8 hours later, which is unusual for me, even on the best of nights. I normally have at least 2 to 3 memorable wakings, so it seems the Sominex had done its job and knocked me out.

Morning grogginess

I definitely didn’t wake up feeling 100% alert. There was a cloudiness in my head, very similar to when I took Nytol – another anti-histamine sleep aid.

It wasn’t terrible, however, and after a strong coffee and shower, I was probably at about 80% normal alertness.

That slightly groggy feeling slowly subsided over the next few hours, and by mid-morning, I was pretty much back to normal.

Testing again the following night

Another hot night, and another Sominex pill to see how it would work two days in a row. Once again, I could feel the sedative effect creeping in just under an hour after taking it. And I again slept all through the night.

I also realized that I normally get woken at least once by insanely noisy seagulls around 5 am. So it was interesting that I slept even through their boisterous cacophony.

The fuzzy head appeared, and as with the previous day, it lasted into the mid-morning before losing the battle to strong coffee.

Would I recommend Sominex?

Sominex undoubtedly worked for me, and I don’t feel that it was just a placebo effect. I’ve had very similar experiences with other anti-histamines, but not with herbal sleep aids.

Personally, I decided not to take it for a third night because I didn’t want more morning grogginess. And the temperature dropped a little anyway, which made it easier to sleep naturally.

So I think it’s one to consider if herbal remedies aren’t quite potent enough for you – as long as you don’t mind a bit of a morning hangover.

Having said that, these anti-histamines do have more safety warnings than herbal remedies. So check both the information below and the patient leaflet, and perhaps even consult your personal doctor before taking it.

Further information

sominex anti-histamine sleep aid package

The following information is taken from the patient leaflet that came with the box of Sominex that I bought from a Boots chemist. Make sure you check yours if you buy it in case there are any changes to the guidance.

Sominex ingredients

  • Promethazine hydrochloride 20mg (the active ingredient).
  • Lactose.
  • Maize starch.
  • Croscarmellose sodium.
  • Magnesium stearate.


One tablet up to an hour before bedtime. If you take more than one, you should tell your doctor immediately or call emergency services.

How long can you take Sominex for?

It’s advised not to use Sominex for longer than 7 days in a row. If you still don’t sleep normally after that, you should consult your doctor before taking more.

Who shouldn’t take Sominex

  • Children under 16.
  • Pregnant or breastfeeding women.
  • People trying to conceive – check with your doctor first.
  • If you’re allergic to promethazine or other ingredients.
  • If you’re allergic to Phenothiazine drugs. These are used for mental illness, nausea/vomiting or vertigo. Examples include chlorpromazine and pericyazine.
  • If you’ve taken MAOI drugs for depression in the last two weeks.
  • Don’t drink alcohol with it.
  • Don’t drive or operate machinery until the effects wear off.


You should consult your doctor before taking Sominex if you have:

  • Asthma.
  • Breathing problems or bronchitis.
  • Have experienced or are receiving treatment for epilepsy.
  • Difficulty peeing.
  • Glaucoma.
  • Prostate, kidney or liver problems.
  • Heart problems.
  • Blocked intestine.
  • Lactose or sugars intolerance.

Interactions with other medicines

Check with your doctor before taking Sominex if you have recently taken, or plan on taking:

  • Any other medication that causes drowsiness.
  • MAOIs for depression.
  • Medicine that gives a dry mouth or blurred vision (e.g. atropine or anti-depressants).
  • Strong painkillers.
  • Medicines for mental illness.
  • Pregnancy tests based on urine samples (risk of false negative results).
  • Allergy skin tests (don’t take Sominex in the three days before the test).

Possible Sominex side effects

Serious side effects

If you experience any of the following, you should stop using Sominex and contact a doctor immediately.

  • An allergic reaction resulting in trouble breathing, mouth or skin swelling, vomiting or stomach pains.
  • Jaundice.
  • Palpitations or change to heart rhythm.
  • Low blood pressure (feeling dizzy or light-headed).
  • Blurred or poor vision, or eye pain.
  • Low energy or interest in doing normal activities.
  • Mouth ulcers, high temperature, bruising easily.
  • Convulsion.

Other possible side effects

Again, if you experience any of these, stop taking Sominex and speak to your doctor.

  • Drowsiness (outside of the time you are trying to sleep).
  • Confusion.
  • Dizziness or headaches.
  • Feeling clumsy or disorientated.
  • Shaking and trembling.
  • Stomach upset.
  • Dry mouth.
  • Difficulty peeing.
  • Feeling restless or excited.
  • Feeling or being sick.
  • Feeling sensitive to sunlight.
  • Trouble sleeping.
  • Ringing noise in the ears.
  • Blocked or stuffy nose.
  • Rashes on the body.

Have you tried Sominex?

If you’ve taken Sominex, or are planning on trying it, it would be useful to hear from you. I know other readers always appreciate seeing a variety of experiences beyond mine.

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