Piriton tablets, Piriton allergy tablets and Piriton syrup all contain the active ingredient chlorphenamine maleate, which is a type of medicine called a sedating antihistamine. Chlorphenamine works by preventing the actions of histamine.

How does Piriton work?

  • Histamine is a substance produced by the body as part of its defence mechanisms. It is stored in cells called mast cells, in almost all tissues of the body. When the body reacts to a foreign substance (known as an allergen, eg flower pollen, pet fur), the mast cells are stimulated by the allergen and release their stores of histamine.
  • The released histamine then binds to its receptors (H1 receptors), causing a chain reaction that results in allergic symptoms.
It causes an increase in blood flow to the area of the allergy, and the release of other chemicals that add to the allergic response.
  • All this results in the symptoms of an allergic reaction. In hayfever, this causes inflammation of the nose, eyes or airways and results in itchy watery eyes, a runny nose, sneezing and nasal congestion. Histamine is also responsible for the symptoms of allergic and itchy rashes, and allergic reactions to foods, medicines or insect bites. It can also cause more severe allergic reactions such as angioneurotic oedema, which involves severe swelling of the eyes, lips, tongue or throat.
  • Piriton works by blocking histamine H1 receptors. It does not prevent the actual release of histamine from mast cells, but prevents it binding to its receptors. This in turn prevents the release of other allergy chemicals and increased blood supply to the area, and provides relief from the typical symptoms of allergies.
  • Piriton is called a sedating antihistamine because it enters the brain in significant quantities and causes drowsiness.
  • The antihistamine action and the fact that it causes drowsiness also make Piriton useful for relieving itching caused by chickenpox. It may be especially helpful for itching that is worse at night. This is often the case in children, who notice itching less during the day when they are active, but are bothered by it at night when they are still and have nothing else to focus on.
  • What is Piriton used for?

    Before taking Piriton

    Before taking Piriton make sure your doctor, dentist or pharmacist knows:

    • If you are pregnant, trying for a baby or breast-feeding.
    • If you have glaucoma.
    • If you have prostate problems, or have been experiencing difficulty passing urine.
    • If you know you have a blockage in your small intestines.
    • If you have liver problems.
    • If you have epilepsy.
    • If you are taking other medicines, including those available to buy without a prescription, herbal and complementary medicines.
    • If you have ever had an allergic reaction to an antihistamine or to any other medicine.

    How to take Piriton

    • Before starting this treatment, read the manufacturer's printed information leaflet from inside the pack.
    • Take Piriton exactly as your doctor advises you. You will be told how many doses to take each day.
    • It is not important whether you take your doses before or after food.
    • If you forget to take a dose, do not worry, take your next dose when it is due. Do not take two doses together to make up for a forgotten dose.

    Getting the most from Piriton

    • Piriton may make you sleepy. If this happens, do not drive or use tools or machines, and do not drink alcohol.
    • If you buy any medicines, check with a pharmacist that they are safe to take alongside Piriton.
    • If you are having an operation or dental treatment, tell the person carrying out the treatment that you are taking an antihistamine.

    Use with caution in

    Not to be used in

    • People who have taken a type of antidepressant called a monoamine oxidase inhibitor (MAOI, eg phenelzine, tranylcypromine or isocarboxazid) in the last 14 days.
    • Piriton tablets and Piriton allergy tablets contain lactose and are not suitable for people with rare hereditary problems of galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption.
    • Piriton syrup contains sucrose and is not suitable for people with rare hereditary problems of fructose intolerance, glucose-galactose malabsorption or sucrose-isomaltase insufficiency.

    This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.
    If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

    Side effects

    Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

    Very common (affect more than 1 in 10 people)

    Common (affect between 1 in 10 and 1 in 100 people)

    Unknown frequency

    • Loss of appetite.
    • Disturbances of the gut such as indigestion, diarrhoea, constipation, vomiting or abdominal pain.
    • Increased energy, restlessness or nervousness (children and elderly people are more susceptible to these types of side effect).
    • Confusion.
    • Irritability.
    • Nightmares.
    • Awareness of your heartbeat (palpitations).
    • Increased heart rate.
    • Abnormal heartbeats (arrhythmias).
    • Sensation of ringing or other noise in the ears (tinnitus).
    • Low blood pressure.
    • Thickening of the mucus in the lungs.
    • Chest tightness.
    • Inflammation of the liver (hepatitis) or jaundice.
    • Skin reactions such as rash, hives or increased sensitivity to sunlight.
    • Difficulty passing urine (urinary retention).
    • Muscle twitching or weakness.

    The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.
    For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

    How can Piriton affect other medicines?

    It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to make sure that the combination is safe.

    You should not use other antihistamines in combination with this medicine. Some cough and cold medicines contain antihistamines, so always check with your pharmacist before taking other medicines in combination with this one.

    This medicine should not be used by people who have taken a type of antidepressant called a monoamine oxidase inhibitor (MAOI) in the last 14 days. This is because side effects such as blurred vision, dry mouth, drowsiness or constipation may be intensified by MAOIs. MAOIs include phenelzine, isocarboxazid and tranylcypromine. For more information ask your pharmacist.

    There may be an increased risk of drowsiness and sedation if this medicine is taken with any of the following (which can also cause drowsiness):

    • alcohol
    • antipsychotics, eg haloperidol, chlorpromazine
    • barbiturates, eg phenobarbital, amobarbital
    • benzodiazepines, eg diazepam, temazepam
    • other sedating antihistamines, eg hydroxyzine, promethazine
    • sleeping tablets, eg zopiclone
    • strong opioid painkillers, eg morphine, codeine, tramadol
    • tricyclic antidepressants, eg amitriptyline, nortriptyline.

    There may be an increased risk of side effects such as dry mouth, blurred vision, urine retention and constipation if Piriton is taken with antimuscarinic medicines that can cause these type of side effects, such as the following:

    • antimuscarinic medicines for Parkinson's symptoms, eg procyclidine, orphenadrine, trihexiphenidyl
    • antimuscarinic medicines for urinary incontinence, eg oxybutynin, flavoxate, tolterodine, propiverine, trospium
    • some antipsychotics, eg chlorpromazine, clozapine
    • antispasmodics, eg hyoscine, atropine
    • tricyclic antidepressants, eg amitriptyline, imipramine.

    Piriton may oppose the effect of histamine (used to treat leukaemia) and is not recommended for people having this treatment.

    Piriton may also oppose the effect of betahistine (used to treat Ménière's disease).

    Piriton may increase the blood level of the antiepileptic medicine phenytoin.

    How to store Piriton

    • Keep all medicines out of the reach and sight of children.
    • Store in a cool, dry place, away from direct heat and light.

    If you have any more questions please ask your Pharmacist.

    Remember to keep all medicines out of reach of children

    Please Note: We have made every effort to ensure that the content of this information sheet is correct at time of publish, but remember that information about drugs may change. This sheet does not list all the uses and side-effects associated with this drug. For full details please see the drug information leaflet which comes with your medicine. Your doctor will assess your medical circumstances and draw your attention to any information or side-effects which may be relevant in your particular case.