Common questions about chlorphenamine - Brand names: Piriton, Allerief, Pollenase

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

When you come into contact with something you're allergic to, such as pollen, animal hair or fur, house dust or insect bites and stings, 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.

Chlorphenamine blocks the effects of histamine and reduces these symptoms.

You should start to feel better within 30 minutes to an hour after taking chlorphenamine.

Chlorphenamine is unlikely to do you any harm if you take it for a long time but it's best to only take it when you need it. Do not take it for longer than 2 weeks without speaking to your doctor.

No, chlorphenamine is not known to be addictive.

Chlorphenamine is known as a drowsy antihistamine because it can make you feel 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 everyday routine.

You might choose to take a drowsy antihistamine if you have a symptom that's keeping you awake, such as itchy skin.

There is not enough information to say whether one antihistamine is better than another for treating allergies. Sometimes you need to try a few before you find one that works best for you.

If you have a very itchy rash, your doctor may advise that you take 2 different antihistamines for a few days.

As well as taking a non-drowsy antihistamine during the day (such as fexofenadine, cetirizine or loratadine), your doctor may recommend a drowsy antihistamine at night time if itching is making it difficult for you to fall sleep.

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

Other drowsy antihistamines include diphenhydramine (Nytol) and promethazine (Phenergan).

Doctors sometimes recommend taking drowsy antihistamines, like chlorphenamine, for a short time to help you sleep if your allergy symptoms keep you awake at night.

But do not take it just for sleep problems without talking to you doctor first, as there may be something better you can take.

If you're having difficulty sleeping (insomnia), there are a number of things you can try to help yourself get 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
• do not watch TV or use phones, tablets or computers before going to bed
• do not 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 this does not work, speak to your doctor.

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

Do not drive a car or ride a bike if chlorphenamine 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 chlorphenamine, 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 chlorphenamine. GOV.UK has more information on the law on drugs and driving.

It's best not to drink alcohol while you're taking chlorphenamine, as it can make you feel very sleepy.

Apart from avoiding alcohol, you can eat and drink normally while taking chlorphenamine.

If you have hay fever, it will help if you do not spend too much time outside when 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.