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Partial agonists bind to and activate a receptor, but are not able to elicit the maximum possible response that is produced by full agonists. The maximum response produced by a partial agonist is called its intrinsic activity and may be expressed on a percentage scale where a full agonist produced a 100% response. A key property of partial agonists is that they display both agonistic and antagonistic effects. In the presence of a full agonist, a partial agonist will act as an antagonist, competing with the full agonistfor the same receptor and thereby reducing the ability of the full agonist to produce its maximum effect. The balance of activity between agonist and antagonist effects varies from one substance to another, according to their intrinsic activities, and is also influenced by the test system used to measure their effects. Weak partial agonists are those compounds, possessing low intrinsic activity, that are able to produce only a small percentage of the total...