In medicine,<unk> is a method to reduce or eliminate an organism's negative reaction to a substance or stimulus. In pharmacology, drug<unk> refers to two related concepts. First,<unk> may be equivalent to drug tolerance and refers to subjects' reactions (positive or negative) to a drug reducing following its repeated use. This is a macroscopic, organism-level effect and differs from the second meaning of<unk>  which refers to a biochemical effect where individual receptors become less responsive after repeated application of an agonist. This may be mediated by phosphorylation, for instance by beta adrenoceptor kinase at the beta adrenoceptor.
Desensitization 
Sensitization 
Cross-tolerance
Reverse tolerance
Co-stimulation
Central tolerance
Counterstimulation
Priming 