Chlorphenamine

What is chlorphenamine?

Chlorphenamine is a sedating antihistamine used to relieve allergy symptoms. It is often sold under brand names such as Piriton and Allerief. Unlike newer “non-drowsy” antihistamines, chlorphenamine can cause sleepiness, which is why it is sometimes referred to as a “drowsy” antihistamine[1]. 

What is chlorphenamine used for?

Chlorphenamine is used to treat a range of allergy-related conditions, including[1]: 

• Hay fever 

• Red, itchy eyes (allergic conjunctivitis) 

• Relief of itching associated with eczema 

• Hives (urticaria), including those caused by food allergies or chickenpox 

• Insect bites and stings 

• Mild allergic reactions (such as those from contrast dye used in scans) 

It is also sometimes included in certain cold and flu medications, particularly when combined with ingredients like pseudoephedrine. 

How does chlorphenamine work?

Chlorphenamine works by blocking histamine H1 receptors in the body[1]. Histamine is a chemical released during allergic reactions that causes symptoms such as itching, swelling, and rashes.

Who can take chlorphenamine?

Chlorphenamine can usually be taken by adults and children over the age of one. Children under 6 years should generally not be given over-the-counter cough and cold medicines containing chlorphenamine (or other antihistamines), due to risk of side effects and limited evidence of benefit for this age group[1]. 

However, it may not be suitable for people with certain medical conditions, such as[1]: 

• Glaucoma 

• Epilepsy 

• An enlarged prostate 

• Breathing difficulties, such as asthma 

• Liver disease 

• High blood pressure 

You should speak to your doctor or pharmacist before taking chlorphenamine, especially if you are pregnant, breastfeeding, or taking any other medication.

Please tell your doctor or pharmacist about any conditions you may have before starting chlorphenamine, and always follow the instructions in the Patient Information Leaflet[2].

How do you take chlorphenamine?

Chlorphenamine is available in several forms. These include tablets, syrup, and, in hospital settings, as an injection (usually only administered by healthcare professionals)[1]. 

Chlorphenamine can be taken with or without food. For liquid forms, always use a proper measuring spoon or oral syringe to ensure the correct dose. 

What is the typical dosage of chlorphenamine?

The dosage of chlorphenamine depends on the age of the person taking it[1]: 

• Adults and children over 12 may take 4mg every 4–6 hours, up to a maximum of 24mg per day. 

• Children aged 6 to 12 may take 2mg every 4–6 hours, with a maximum of 12mg per day. 

• Children aged 1 to 5 and weighing over 10kg may take 1mg every 4–6 hours, with a maximum of 6mg per day. Dosage for children under 2 years should be determined by a doctor or pharmacist. 

Always follow the dosage instructions provided by your doctor or pharmacist, or listed on the packaging. 

Can you stop taking chlorphenamine suddenly?

Yes, chlorphenamine is not addictive, so you can stop taking it once your allergy symptoms improve. There are usually no withdrawal effects from stopping it. 

What should you do if you take too much chlorphenamine?

If you suspect you have taken too much chlorphenamine, seek immediate medical attention or call 999[1]. Signs of chlorphenamine overdose may include extreme drowsiness, confusion, a fast or irregular heartbeat, or seizures. The amount needed to cause an overdose may vary from person to person. Overdose can be particularly dangerous in young children. 

What should you do if you forget a dose of chlorphenamine?

If you miss a dose of chlorphenamine, you can take it as soon as you remember. However, if it is nearly time for your next dose, skip the missed one, and do not take a double dose to make up for the missed one. 

Which medicines should you avoid while taking chlorphenamine?

Do not take chlorphenamine with[1]: 

• Other sedating (drowsy) antihistamines 

• Alcohol 

• Sleeping pills or tranquilisers 

• Certain antidepressants, particularly tricyclic antidepressants (e.g., amitriptyline) and monoamine oxidase inhibitors (MAOIs - now rarely used) 

• Other medicines with sedative effects (e.g., some epilepsy medicines, anxiety medicines (benzodiazepines), strong painkillers (opioids), some anti-sickness medicines) 

Always check with your pharmacist or GP before combining chlorphenamine with any other medicines, including herbal remedies (especially those causing drowsiness like valerian) and over-the-counter medicines. 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2].

What are the side effects of chlorphenamine?

The most common side effects of chlorphenamine occur in more than 1 in 100 people, and include[1]: 

• Drowsiness 

• Dizziness 

• A dry mouth 

• Headaches 

• Blurred vision 

• Difficulty concentrating 

Some less common side effects of taking chlorphenamine may include: 

• Nausea or vomiting 

• Constipation or diarrhoea 

• Difficulty passing urine (urinary retention) 

Important: This is not a complete list. Always read the leaflet in your medicine packet for full information. You must not drive, cycle, or use heavy machinery if you feel drowsy or dizzy, or if your vision is blurred. This medicine can affect your ability to perform these activities safely. 

Frequently asked questions about chlorphenamine

Can I drink alcohol while taking chlorphenamine? 

It is best to avoid drinking alcohol while taking chlorphenamine as it can cause and increase drowsiness[1]. 

Is chlorphenamine safe to take during pregnancy? 

You should only take chlorphenamine during pregnancy if it is recommended by your doctor or pharmacist[1]. 

Can I take chlorphenamine long-term? 

It is not usually recommended to take chlorphenamine regularly for long periods without medical supervision, especially for the elderly. If your symptoms last longer than two weeks or keep coming back, speak to your GP or pharmacist. Long-term use can increase the risk of side effects [1]. 

Is chlorphenamine available over the counter? 

Yes, some forms of chlorphenamine are available in pharmacies without a prescription, however injections do require a prescription. However, it is typically intended for short-term use only – usually no more than two weeks without consulting a healthcare professional[1]. 

How long does chlorphenamine take to work? 

You should begin feeling better around 30 minutes to an hour after taking chlorphenamine[1]. 

Can you take more than 1 chlorphenamine or antihistamine at a time? 

No, you should generally not take more than one antihistamine at the same time, unless specifically advised by a doctor or pharmacist. Do not take extra doses of chlorphenamine beyond the recommended amount on the packet or by your doctor or pharmacist. Taking multiple sedating antihistamines together significantly increases the risk of serious side effects like severe drowsiness, confusion, and breathing difficulties[1]. 

Can I drive a vehicle or ride on a bike if I’m taking chlorphenamine? 

You must not drive, cycle, or use heavy machinery if you feel drowsy or dizzy, or if your vision is blurred. This medicine can affect your ability to perform these activities safely[1]. 

For the official NHS guide to chlorphenamine, visit their website.