Which of the following is classified as a Schedule I drug?

Heroin is classified as a Schedule I drug under the Controlled Substances Act. This classification is given to substances that have a high potential for abuse, do not have an accepted medical use in treatment in the United States, and lack accepted safety for use under medical supervision. Heroin is an opioid that has no currently accepted medical applications, making it illegal to manufacture, sell, or possess.

In contrast, the other substances listed—cocaine, fentanyl, and methamphetamine—are classified as Schedule II drugs. This means that while they also have a high potential for abuse, they do have some accepted medical uses and can be prescribed by medical professionals under regulated conditions.