Antihistamines are medicinesoften used torelieve symptoms of allergies, such ashay fever, hives, conjunctivitisand reactions to insect bites or stings.
They're also sometimes used to preventmotion sickness, to treat feeling sick (nausea) or being sick (vomiting),and as a short-term treatment forinsomnia.
Most antihistamines can be boughtfrom pharmacies and shops, but some are only available on prescription.
Typesof antihistamine
There aremany types of antihistamine.
They're usually divided into2 main groups:
- antihistamines that make you feelsleepy– such as chlorphenamine (Piriton), cinnarizine, diphenhydramine, hydroxyzine and promethazine
- non-drowsyantihistamines that are less likely to make you feel sleepy– such as acrivastine,cetirizine, fexofenadine and loratadine
They also come in several different forms– includingtablets, capsules, liquids, syrups, creams, lotions, gels, eyedrops and nasal sprays.
Which type is best?
There'snot muchevidence to suggest any particularantihistamine is better than any other at relieving allergy symptoms.
Some people findcertain types work well for them and others do not. You may need to try several types to find one that works for you.
Non-drowsy antihistamines are generally the best option, as they're less likely to make you feel sleepy. But types that make you feel sleepy may be better if your symptoms stop you sleeping.
Ask a pharmacist for advice if you're unsure which medicine to try as not all antihistamines are suitable for everyone.
Howto take antihistamines
Take your medicine as advised by the pharmacist or doctor, or as described in the leaflet that comes with it.
Before taking an antihistamine, you should know:
- how to take it – including whether it needs to be taken with water or food, or how to use it correctly(ifeyedrops or a nasal spray)
- how much to take (the dose)– this can vary depending on things such as your age and weight
- when to take it– including how many times a day you can take it andwhen to take it (some types shouldbe taken before bedtime)
- how long to take it for– some types can be used for a long time, but some are only recommended for a few days
- what to do if you miss a dose or take too much (overdose)
The advice varies depending on the exact medicine you're taking. If you're not sure how to take your medicine, ask a pharmacist.
Sideeffects of antihistamines
Like all medicines, antihistamines can cause side effects.
Side effects of antihistamines that make you drowsy can include:
- sleepiness (drowsiness) and reduced co-ordination, reaction speed and judgement– do not drive or use machinery after taking these antihistamines
- dry mouth
- blurred vision
- difficulty peeing
Side effects ofnon-drowsy antihistamines caninclude:
- headache
- dry mouth
- feeling sick
- drowsiness– this is less common with non-drowsy antihistamines but is still possible
Check the leaflet that comes with your medicine for a full list of possible side effects and advice about when to get medicalhelp.
If you think your medicine has caused an unwanted side effect, you can report it through the Yellow Card Scheme.
Takingantihistamines with other medicines, food or alcohol
Speak toa pharmacist or GP before taking antihistamines if you're already taking other medicines.
There may be a risk the medicines do not mix, which could stop either from working properlyor increase the risk of side effects.
Examples of medicines thatcouldcause problems if takenwith antihistamines include some types of:
- antidepressants
- stomach ulcer orindigestion medicines
- coughandcold remedies that also contain an antihistamine
Try not to drink alcohol while taking an antihistamine, particularly if it's a type that makes you drowsy,as it can increase the chances of it making you feel sleepy.
Food and other drinks do not affect most antihistamines, but check the leaflet that comes with your medicine to make sure.
Whocan take antihistamines
Most people can safely take antihistamines.
But speak to a pharmacist or GPfor adviceif you:
- arepregnantor breastfeeding
- are looking for a medicine fora youngchild
- are an older person
- are taking other medicines
- have an underlying health condition, such as heart disease,liver disease, kidney disease orepilepsy
Some antihistamines may not be suitable in these cases. A pharmacist or doctor can recommend one that's bestfor you.
Loratadine is usually recommended if you need to take an antihistamine in pregnancy. Loratadine or cetirizine are usually OK to take while breastfeeding.
Always check the leaflet that comes with yourmedicine to see if it's safe for you before taking it or giving it to your child.
Howantihistamines work
Antihistamines block the effects of a substance called histamine in your body.
Histamine is normally released when your body detects something harmful, such as an infection. It causes blood vessels to expand and the skin to swell, which helpsprotect the body.
But in people with allergies, the body mistakes something harmless – such as pollen,animal hair or house dust – for a threat and produces histamine. The histamine causes an allergic reaction with unpleasant symptoms including itchy, watering eyes, a running or blocked nose, sneezing and skin rashes.
Antihistamines help stop this happening if you take them beforeyou come into contact with the substance you're allergic to. Or they can reduce the severity ofsymptoms if you take them afterwards.
Find out more about your medicine
The leaflet that comes in the packet with your medicine will have detailed information about it, including how to take it and what side effects you might get.
If you no longerhave the leaflet that came with your medicine, you can search for an online versionof it using our medicines A to Z.
You may also find information on individual antihistamines onthese websites:
Page last reviewed: 16 May 2023
Next review due: 16 May 2026
