Agonist drugs, which interact with a receptor mimicking the effect of a natural mediator
Partial agonist drugs, whose maximal response falls short of the full response
Antagonists block the effect of the natural mediator at a receptor to prevent an effect
Selective, but not specific, drugs (which act on more than one receptor and produce side-effects, which lead to dry mouth, blurred vision, constipation and drowsiness)
Inhibiting enzymes in the body