A<unk>  is a drug which blocks<unk>  receptors (of which there are five types in the human body; they are found in the brain, peripheral nervous system, blood vessels, and the kidney).
Dopamine antagonist
Dopamine agonist
Serotonin antagonist
Nicotinic antagonist
Adrenergic agonist
Alpha-adrenergic agonist
Muscarinic antagonist
Muscarinic agonist