These were some of the first antihistamines scientists developed. They also work in the part of the brain that controls . One of the most common side effects of first-generation antihistamines is feeling sleepy.
For this reason, they are sometimes used to help people who have trouble sleeping (insomnia).
They do not always completely control the allergic reaction because they do not counteract other chemicals that may be responsible for the symptoms.
There are at least two kinds of histamine receptors, hence are mainly H1 blockers.
To get a good idea of what histamine can do, let us imagine the effects of an injection of a small amount of histamine: Headache is felt as a pulsating, whole-head pain, often with a sense of pressure.
Fast heart, blood pressure falls, irregular beats with alarming palpitations.
These are meant to treat many symptoms at the same time.
They are available in pills or liquids, nasal sprays or gels, and eyedrops. This can cause itching, sneezing, runny nose, and watery eyes.
Two types of OTC antihistamines are available: first-generation and second-generation. First-generation antihistamines are sometimes used in OTC . Antihistamines prevent histamines from attaching to your cells and causing symptoms.
Agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed antihistamines; other agents may have antihistaminergic action but are not true antihistamines.
In common use, the term "antihistamine" refers only to H In type I hypersensitivity allergic reactions, an allergen (a type of antigen) interacts with and cross-links surface Ig E antibodies on mast cells and basophils.