Common questions about promethazine - Brand names: Phenergan, Sominex

Promethazine is a medicine called an antihistamine. It's classed as a drowsy (sedating) antihistamine.

When you come into contact with something you're allergic to, such as pollen or animal hair, your body produces a chemical called histamine. Usually, histamine is a useful substance, but in an allergic reaction it causes symptoms including itchy, watery eyes, a running or blocked nose, sneezing and skin rashes.

Promethazine blocks the effects of histamine in your brain and this reduces symptoms.

It enters the brain in large quantities and this can make you feel drowsy.

Promethazine also blocks the effects of a chemical called dopamine, and this stops you feeling sick.

Promethazine will start to make you feel sleepy around 20 minutes after you take it and may work for up to 12 hours.

If you're taking it for a cough or cold, allergies or feeling sick (nausea), your symptoms should start to improve within 20 minutes. The medicine should work for around 4 to 6 hours.

It's unlikely that you'll get addicted to promethazine. But it's best that you only take it for a very short time, unless your doctor tells you to take it for longer.

If you've bought a medicine containing promethazine, do not take it for longer than recommended on the packet without speaking to your pharmacist or doctor first.

If you've taken promethazine for a long time and suddenly stop taking it, it's possible you might feel dizzy, sweaty or sick, have a racing heart and have trouble sleeping.

Coming off promethazine slowly can help prevent this.

Speak to your doctor if you have taken promethazine for a long time and want to stop taking it.

Promethazine blocks the effects of a natural chemical called acetylcholine.

This can help dry up a cough or runny nose but can also cause side effects such as a dry mouth and dry nose.

Some cough and cold remedies claim to suppress your cough or stop you bringing up phlegm.

Although some people find them helpful, they're not usually recommended.

This is because there's little evidence that they're any more effective than simple home remedies and they're not suitable for everyone.

Promethazine is known as a drowsy (sedating) antihistamine as it makes you sleepy.

Non-drowsy antihistamines are less likely to have this effect. These include cetirizine, fexofenadine and loratadine.

Most people prefer to take a non-drowsy antihistamine as it's less likely to interfere with their normal routine.

You might choose to take a drowsy antihistamine, however, if you're having problems falling asleep, or if symptoms like itching or coughing are keeping you awake.

There's not enough information available to say whether one antihistamine is better than another for treating allergies.

You may need to try a few different medicines to find what works best for you. Ask your pharmacist or doctor for advice if you're unsure.

You can take 2 different antihistamines at a time if your doctor says it's OK. If you have a severe itchy skin rash, your doctor may recommend 2 different antihistamines together for a few days.

You could take a non-drowsy antihistamine (such as cetirizine, fexofenadine or loratadine) during the day, and a drowsy antihistamine at night if itching is making it difficult to sleep.

Do not take another drowsy antihistamine together with promethazine. It'll make you very tired and sleepy.

Other drowsy antihistamines include chlorphenamine (Piriton) and diphenhydramine (Nytol Original).

If you take it for short-term sleep problems or take it at bedtime, promethazine will help you sleep.

If you take it during the day for other conditions, such as allergies, it might make you feel sleepy during the day as well.

Promethazine does not affect any type of contraception, including the combined pill and emergency contraception.

Do not drive a car or ride a bike if promethazine makes you sleepy during the daytime, gives you blurred vision or makes you feel dizzy, clumsy or unable to concentrate or make decisions.

This may be more likely when you first start taking promethazine, but could happen at any time, for example, when starting another medicine.

It's an offence to drive a car if your ability to drive safely is affected. It's your responsibility to decide if it's safe to drive. If you're in any doubt, do not drive.

Talk to your doctor or pharmacist if you're unsure whether it's safe for you to drive while taking promethazine. GOV.UK has more information on the law on drugs and driving.

Do not drink alcohol while you're taking promethazine.

Alcohol and promethazine together can make you sleep very deeply.

You will not be able to breathe properly and may have difficulty waking up.

You can eat normally while taking promethazine.

However, do not drink alcohol.

If you take promethazine to help you sleep, try not to have drinks that contain caffeine, like coffee, tea, cola or energy drinks. Caffeine has the opposite effect to promethazine and can stop the medicine working.

Yes, it's dangerous to take promethazine with recreational drugs. This is because it can slow or stop your heart and lungs.

Mixing promethazine and codeine in large amounts slows down the central nervous system (brain and spinal cord), which can slow breathing and heart rate.

It's even more dangerous when taken with alcohol or recreational drugs and has caused people to die.

Find out more about the side effects of recreational drugs on the Frank website.

Your doctor will usually recommend lifestyle changes to improve your sleep before trying medicines.

There are a number of things you can try to help you have a good night's sleep. You could:

• set regular times for going to bed and waking up
• relax before bedtime – try taking a warm bath or listening to calming music
• use thick curtains or blinds, an eye mask and earplugs to stop you being woken up by light and noise
• avoid caffeine, cigarettes or vapes, alcohol, heavy meals and exercise for a few hours before bedtime
• avoid watching TV or using phones, tablets or computers before going to bed
• try not to nap during the day
• make a list of your worries and any ideas for how to solve them before you go to bed – this can help you forget about them until the morning

If you have hay fever, it helps if you do not spend too much time outside if the pollen count is high.

Tips for when you're outside:

• Do not cut grass or walk on grass.
• Wear wraparound sunglasses to stop pollen getting into your eyes.
• Put Vaseline around your nostrils to help trap pollen.
• Shower and change your clothes after you've been outside to wash off pollen.

Tips for when you're inside:

• Keep windows and doors shut as much as possible.
• Vacuum regularly and dust with a damp cloth.
• Do not keep fresh flowers in the house.
• Do not smoke or be around smoke as it makes hay fever symptoms worse.

The best way to prevent any sort of allergic reaction is to avoid the substance that you're allergic to, if you can.

There are some practical steps you can follow to help prevent allergies.