An agonist is a drug that binds to the receptor and generates a required or full response to the intended chemical and receptor in the brain but an antagonist is a drug that binds to the receptor and hinders the receptor from producing a response. This is important to enable drugs to produce the required effect that is individualized for each patient. Agonists cause an action and antagonist opposes the action. Agonists are drugs with both affinity and inherent efficacy. In other words, agonists attach to the target receptor and can modify the receptor activity to generate a response. Antagonists on the other hand have affinity but no inherent efficacy; hence they can stick to the target receptor and do not generate any response. Antagonist generally minimizes the probability of occupancy by an agonist by virtue of occupying a portion of the receptor population.