Certified Addiction Counselor (CAC) 2025 – 400 Free Practice Questions to Pass the Exam

An agonist in pharmacology refers to a substance that mimics or facilitates the action of a neurotransmitter. This means that an agonist binds to a receptor in the brain and activates it, thereby triggering a response similar to that induced by the naturally occurring neurotransmitter. For example, substances like morphine act as agonists at opioid receptors, producing effects that can range from pain relief to euphoria, paralleling the effects of endogenous opioids.

The other definitions provided do not accurately describe an agonist's role. A chemical that neutralizes neurotransmitter effects would describe an antagonist, which blocks or dampens a response by preventing neurotransmitter action. Medications aimed at inhibiting drug dependence typically focus on different mechanisms, such as stabilizing mood or reducing cravings, rather than mimicking neurotransmitter action directly. Lastly, medications used primarily for withdrawal symptoms often serve a different purpose, such as alleviating the symptoms caused by the absence of a drug rather than acting as an agonist at neurotransmitter receptors. Hence, the definition of an agonist as something that mimics or facilitates neurotransmitter action is clear and precise.