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.(Whereas, in the stomach, histamine made by cells that line the stomach helps to produce acid for food digestion.)Your immune system cells monitor your blood and mucosae for anything (for example, germs such as bacteria or viruses) that is not made by your body.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.For example: For other conditions, specific antihistamines may be used.For example, cyclizine and promethazine teoclate are used for feeling sick (nausea) and being sick (vomiting), not for hay fever.(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 peak of effectiveness is typically within 1-2 hours after being taken.
Chlorphenamine is the antihistamine most used in an emergency situation such as anaphylaxis, and may be given by injection in this situation.