Receptor agonists are drugs that have both receptor affinity and intrinsic activity and bind to the receptor of some ligand, agitating the receptor and presenting an interaction with that ligand. Receptor agonists are categorized as full agonists and partial agonists; full agonists have strong affinity and intrinsic activity, while partial agonists have strong affinity but weaker intrinsic activity. Both act on the same receptor and compete with each other at the binding site of the receptor. For example, morphine and pentazocine both act at opioid receptors; morphine is a full agonist with a strong analgesic effect, while pentazocine is a partial agonist with a weaker analgesic effect that competes to counteract the effects of morphine at high doses. After long-term use of receptor agonists, there will be a decrease in the number of receptors, a decrease in responsiveness to receptor agonists, and a desensitization effect. Therefore, patients should use the drug reasonably under the guidance of the doctor.