#health #medicine #drug #biology


Histamines are generated by mast-cells and basophils. There are four types or receptors (H1-H2-H3-H4), with various functions. H1 is the major type playing a role in immune response. H1 receptors result in vasodilation of vessels. The consequence can be swelling, sensation of heat, hives, hitching, sneezing, airways constriction, etc. Allergies are caused by secretion of histamines on detection of a foreign molecule incorrectly recognized as a pathogen.

Anti-histamines are molecules that act as antagonists on the H1 receptors. They block the effect of histamines in the receptor. H1 receptors can also active themselves without histamines ; anti-histamin have a reverse agonist role that reduces this basal effect of the receptors.

Anti-histamines are mostly effective as prevention, and don't work as well once the immune response is triggered.

First generation anti-histamines (e.g. diphenhydramine aka benadryl) were small molecules and tended to easily cross the blood-brain barrier, resulting in sedation and drowsiness.

Second generation anti-histamines (e.g. cetirizine, loratidine...) are lypophobic, and tend not to cross the barrier as much, reducing the drowsiness.


Anti-histamines can help with Common cold symptoms, by reducing the effects of immune response.


Professor dave/Anti histamines