Agonist
The agonist is an endogenous material or a medicine which can interreact with receptors and initiate physiological or pharmacological characteristics of the response of a receptor.
Intensity of biological responses (analgesia) educing under the influence of opioids, can be used for definition of their true activity. Opioids, such as Morphinum, Fentanylum, which maximum biological effect it is caused by linkage of receptors, name agonists.
Full agonists invoke the maximum biological response (for example, an analgesia, a respiratory depression).