Which of the following substances is classified as a Schedule III controlled substance?

Buprenorphine is classified as a Schedule III controlled substance primarily due to its medical uses and potential for abuse. Schedule III substances have a moderate potential for physical dependence and a less potential for psychological dependence compared to Schedule I and II substances. Buprenorphine is widely used in the treatment of opioid addiction and pain management, which allows it to be prescribed by qualified practitioners while still adhering to regulations designed to control its distribution and prevent misuse.

In contrast, the substances listed in the other choices fall into different schedules based on their abuse potential and accepted medical uses. Alprazolam, often prescribed for anxiety and panic disorders, is classified as a Schedule IV drug, indicating a lower potential for abuse compared to Schedule III substances. Chlordiazepoxide, used for anxiety and alcohol withdrawal, is also classified as Schedule IV. Phenobarbital, which has a long history of being used for seizures, is classified as Schedule IV as well. Understanding these classifications helps in recognizing how substance abuse potential and medical utility impact regulation and prescription practices.