Final answer:
An agonist is a drug that increases the activity of a specific neurotransmitter by either promoting its synthesis, reducing its reuptake, or mimicking its action at the receptor site.
Step-by-step explanation:
An agonist is a drug that increases the activity of a specific neurotransmitter by either promoting its synthesis, reducing its reuptake, or mimicking its action at the receptor site. They bind to receptors and produce a similar effect to the endogenous ligand. For example, dopamine agonists are commonly used in the treatment of Parkinson's disease to mimic the effects of dopamine.