How does it work?
Periactin tablets contain the active ingredient cyproheptadine, which is a type of medicine called a sedating antihistamine.
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), 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 hay fever, it 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.
Cyproheptadine works by blocking histamine H1 receptors. It doesn't 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.
Cyproheptadine 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 cyproheptadine useful for relieving itching caused by allergies, chickenpox or eczema. 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.
Cyproheptadine is also used in the treatment of migraine attacks and other similar headaches (vascular headaches). It is not fully understood how it works in this condition. However, in addition to blocking the actions of histamine, cyproheptadine is also known to block the action of a chemical in the brain called serotonin. These chemicals are involved in migraine. The medicine may be helpful for people whose headaches are not relieved by other migraine treatments; the characteristic headache and feeling sick may disappear within an hour or two of the first dose.
What is it used for?
- Relieving the symptoms of allergic conditions such as hay fever, pet allergies, dust mite allergies, nettle rash (urticaria), food allergies and reactions to insect bites or medicines.
- Relieving the symptoms of a more serious allergic reaction called angioneurotic oedema, which causes swelling of the eyes, lips, tongue or throat.
- Relieving itching associated with chickenpox or eczema.
- Relieving migraine and vascular headaches.
How do I take it?
- For relieving the symptoms of allergies, adults, adolescents and children aged 14 years and over should take one Periactin tablet three times a day to start with. If this does not relieve symptoms the dose can be increased to up to a maximum of eight tablets in 24 hours. Elderly people should avoid taking this medicine.
- For relieving the symptoms of allergies, children aged 7 to 14 years can be given one tablet two or three times a day, depending on age and weight of the child. If necessary a further dose of one tablet can be given at bedtime. Do not give this age group more than four tablets in 24 hours.
- For relieving the symptoms of allergies, children aged 2 to 6 years can be given half a tablet two or three times a day. If necessary a further dose of half a tablet can be given at bedtime. Do not give this age group more than three tablets in 24 hours.
- To treat a migraine, adults should take one tablet when you first notice you are getting the migraine. Take another tablet if needed after 30 minutes. Then take one tablet every four to six hours to maintain relief if necessary. Do not take more than two tablets in any four to six hour period.
- The tablets can be taken either with or without food.
- Do not exceed the recommended dose.
- If symptoms persist despite treatment, seek medical advice from your doctor or pharmacist.
- This medicine may cause drowsiness, blurred vision or dizziness. If affected do not drive or operate machinery. If children are affected they should avoid potentially hazardous activities such as riding bikes or climbing trees.
- You should not drink alcohol while taking this medicine as it is likely to make any drowsiness or dizziness worse.
- If you are due to have any skin prick or patch tests to diagnose allergies you should stop taking your antihistamines at least 48 hours before the tests. This is because antihistamines can prevent or lessen the skin reactions that indicate an allergy, and so can make the test results unreliable.
Use with caution in
- Children (who are also more prone to potential side effects).
- A condition called bronchiectasis, in which there is persistent and progressive widening of the airways due to lung infections or lung disease, such as cystic fibrosis.
- Men with an enlarged prostate gland (prostatic hypertrophy).
- People with raised pressure in the eye.
- Liver disease.
- People with cardiovascular disease.
- People with high blood pressure (hypertension).
- People with an overactive thyroid gland (hyperthyroidism).
- Hereditary blood disorders called porphyrias.
Not to be used in
- Children under two years of age.
- Elderly, weak or debilitated people.
- People who have taken a type of antidepressant called a monoamine oxidase inhibitor (MAOI, eg phenelzine, tranylcypromine or isocarboxazid) in the last 14 days.
- People having treatment for an asthma attack.
- People with a blockage of the opening from the stomach into the intestines (pyloro-duodenal obstruction).
- People with a peptic ulcer that is causing narrowing in the gut (stenosing peptic ulcer).
- People with a blockage of the drainage of urine out of the bladder (bladder neck obstruction) or difficulty passing urine (urinary retention), for example due to an enlarged prostate gland.
- Periactin tablets contain lactose and are not suitable for people with rare hereditary problems of galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption.
This medicine should not be used if you are allergic to 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.
Pregnancy and breastfeeding
Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
- The safety of this medicine for use during pregnancy has not been established. If you are pregnant you should not take this medicine without consulting your doctor for advice first. It should be used with caution during pregnancy, and only if the expected benefit to the mother is greater than any possible risk to the developing baby.
- It is not known if this medicine passes into breast milk. However, as it could potentially be harmful to a nursing infant, you should not take this medicine if you are breastfeeding. Seek further medical advice from your doctor.
- This medication may cause drowsiness. If affected do not drive or operate machinery. Avoid alcoholic drink.
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 does not mean that all people using this medicine will experience that or any side effect.
- Drowsiness or sleepiness (in many people this wears off after three to four days of treatment).
- Problems with co-ordination.
- Blurred or double vision.
- Difficulty passing urine (urinary retention).
- Disturbances of the gut such as diarrhoea, constipation, nausea, vomiting or abdominal pain.
- Dry mouth, nose or throat.
- Wheezing or difficulty breathing.
- Low blood pressure (hypotension).
- Awareness of your heartbeat (heart palpitations).
- Increased heart rate.
- Excitement in children.
- Difficulty sleeping (insomnia).
- Changes in appetite.
- Weight gain.
- Pins and needles sensations.
- Liver problems.
- Blood disorders.
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 this medicine 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):
- antipsychotics, eg haloperidol, chlorpromazine
- barbiturates, eg phenobarbital, amobarbital
- benzodiazepines, eg diazepam, temazepam
- other sedating antihistamines, eg hydroxyzine, promethazine, chlorphenamine
- 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, difficulty passing urine and constipation if cyproheptadine 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.
Due to its serotonin blocking action in the brain, cyproheptadine may possibly oppose the antidepressant effect of SSRI antidepressants such as fluoxetine, paroxetine or citalopram.
Cyproheptadine may oppose the effect of histamine (used to treat leukaemia) and is not recommended for people having this treatment.
Cyproheptadine may also oppose the effect of betahistine (used to treat Ménière's disease).
Other medicines containing the same active ingredient
There are currently no other medicines available in the UK that contain cyproheptadine as the active ingredient.