Some antihistamines may also have what is known as an antimuscarinic effect.
This means that the medicine can also block another type of receptor found on the surface of certain cells.
The brain has several key areas which control vomiting.
These effects are mainly caused by the older first-generation antihistamines which are described below.
Note: antihistamines should not be confused with H2 blockers which reduce the production of stomach acid.
Antihistamines are a group of medicines which act by blocking the action of the chemical called histamine in the body.
Either H1 or H2 histamine receptors can be blocked by medicines, but the group commonly known as antihistamines blocks the H1 receptor.
Your doctor or pharmacist will advise you on how to take your medication, including what dose and how often.
Read the leaflet that comes with your particular brand for further information.
(Mucosae are membranes lining body cavities such as your mouth, nose and digestive tract.) If your skin is damaged or your immune system detects a foreign substance, histamine is released from mast cells.
The histamine binds to special sites (receptors) on other cells, called H1 receptors.
While this is a helpful response, it also causes redness, swelling and itching.
Allergic reactions such as hay fever (seasonal allergic rhinitis) are caused by an oversensitivity or over-reaction of the immune system to a particular allergen.
This is one of the most common uses of antihistamines. For example: Histamine is a chemical naturally produced by various cells in your body. Large amounts of histamine are made in cells called mast cells, in places where the body comes into contact with the outside environment. Here, mast cells and histamine form part of your immune defence system.