Which of the following substances is classified as a Schedule I (C1) drug?

Heroin is classified as a Schedule I (C1) drug primarily due to its high potential for abuse and lack of accepted medical use in treatment in the United States. Schedule I substances are considered the most dangerous in terms of addiction and potential for abuse, and they cannot be prescribed by healthcare providers.

Heroin is an opioid that has no accepted therapeutic purpose, which is why it falls into this category. It is important for public health and safety that such substances are strictly regulated, reflecting their high risk of addiction and significant harm to individuals and society if used improperly. In contrast, the other substances listed—fentanyl, hydrocodone, and buprenorphine—are classified under different schedules due to their accepted medical uses and varying risks associated with their use.