Certain people are advised to speak with a GP before taking a common antihistamine. The medication is used to relieve symptoms of insect bites, eczema, conjunctivitis and chickenpox, as well as allergies like hay fever, and is available on prescription and in pharmacies.

Although you might not be familiar with chlorphenamine, you've probably heard of Piriton, Allerief or Pollenase, which all contain it as a main active ingredient. Most adults and children aged over one year old can take chlorphenamine, but there are 12 main groups who should always take caution.

According to the NHS, this includes anyone with the following symptoms, who should always speak with a doctor or pharmacist first:

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The health service also adds: "If you or your child has been prescribed chlorphenamine, follow your doctor's instructions about how and when to take it.

"If you've bought chlorphenamine or any medicine containing chlorphenamine from a pharmacy, follow the instructions that come with the packet, or ask your pharmacist for advice. If you or your child's symptoms do not get better within a few days, talk to a doctor."

People taking chlorphenamine should also be mindful when combining it with other medications to avoid side effects. Check with a doctor or pharmacist if you're already taking medications such as:

• A type of antidepressant called a monoamine oxidase inhibitor, such as phenelzine


• Phenytoin (an anti-epilepsy medicine)


• Any medicines for anxiety or to help you sleep


• Any medicine that makes you drowsy, gives you a dry mouth, or makes it difficult for you to pee – taking chlorphenamine might make these side effects worse

Children under six years old should also not take cough or cold medicines containing chlorphenamine alongside other ingredients. However, NHS guidance warns: "These are not all the medicines that may cause problems if you take them with chlorphenamine. For a full list, see the leaflet inside your medicine packet."

It adds: "It's safe to take chlorphenamine with painkillers like paracetamol or ibuprofen that you buy from a pharmacy or shop. But if you take chlorphenamine with painkillers that contain codeine (such as co-codamol) or other prescription painkillers, you're more likely to have side effects."

Chlorphenamine generally starts working within 30 minutes to an hour, and users should wait at least four hours before taking another dose. Typical side effects include nausea, dizziness, headaches, sleepiness, blurred vision and difficulty concentrating.

Anyone experiencing dizziness, sleepiness, or blurred vision should avoid riding a bike or driving a car until their symptoms resolve. Alcohol should also be avoided when taking chlorphenamine.

For more information, visit theNHS website here.

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