Meaning of Desensitization

Repeated exposures to a drug may result in a decreased drug response. Desensitization is caused by changes to drug receptors (especially proteins) that decrease drug-receptor binding or reduce receptor site activation when binding occurs. 

When desensitization occurs, the effects can be limited to a single receptor or may influence multiple receptors. When drug-receptor binding involves a second messenger, the result may be desensitization to the effects that would have been produced by binding to multiple receptors (i.e., all of the receptors normally activated by binding of the drug to its primary receptor).

Desensitization may be used therapeutically to minimize allergic reactions (e.g. allergy shots).