Histamine is a chemical released when the body detects something harmful, such as an infection.It causes blood vessels to expand and the skin to swell (known as inflammation), which helps protect the body.Antihistamines help stop this happening if you take them before you come into contact with the substance you're allergic to.Or they can reduce the severity of symptoms if taken afterwards.Examples of medicines that could cause problems if taken with antihistamines include some types of: It's best to avoid alcohol while taking an antihistamine, particularly if you're taking an older type of antihistamine, as this can increase the chances of it making you feel sleepy.Food and other drinks don't affect most antihistamines, but check the leaflet that comes with your medicine to make sure.
If you think your medicine has caused an unwanted side effect, you can report it through the Yellow Card Scheme.
When your body comes into contact with whatever your allergy trigger is -- pollen, ragweed, pet dander, or dust mites, for example -- it makes chemicals called histamines.
They cause the tissue in your nose to swell (making it stuffy), your nose and eyes to run, and your eyes, nose, and sometimes mouth to itch.
There's not much evidence to suggest any particular antihistamine is better than any other at relieving allergy symptoms.
Some people find certain types work well for them and others do not.
Speak to a pharmacist or your GP before taking antihistamines if you're already taking other medicines.