In
pharmacology,
partial agonists are drugs that bind to and activate a given
receptor, but have only partial
efficacy at the receptor relative to a
full agonist. They may also be considered
ligands which display both
agonistic and
antagonistic effects — when both a full agonist and partial agonist are present, the partial agonist actually acts as a
competitive antagonist, competing with the full agonist for receptor occupancy and producing a net decrease in the receptor activation observed with the full agonist alone. Clinically, partial agonists can be used to activate receptors to give a desired submaximal response when inadequate amounts of the endogenous ligand are present, or they can reduce the overstimulation of receptors when excess amounts of the endogenous ligand are present.