Which of the following substances is classified as Schedule I?

Heroin is classified as Schedule I under the Controlled Substances Act, primarily due to its high potential for abuse and lack of accepted medical use in the United States. Schedule I substances are considered to have no currently accepted medical use and pose a significant risk of physical or psychological dependence.

In contrast to Schedule I drugs, other substances listed, like flunitrazepam, codeine, and tramadol, are classified in different schedules based on their medical use, potential for abuse, and safety profile. For example, flunitrazepam is a Schedule IV drug due to its accepted medical use, as well as its lower potential for abuse compared to Schedule I substances. Codeine is classified as a Schedule II or III substance depending on its formulation and strength. Tramadol, while it has pain-relieving properties, is classified as a Schedule IV substance because it has a lower potential for abuse compared to heroin and is accepted for medical use. This system of classification helps in the regulation and control of substances based on their associated risks and benefits.