How is Schedule I defined in terms of medical use?

Schedule I drugs are classified as substances that are not accepted for medical use in the United States. This classification is significant because it denotes that these substances are deemed to have a high potential for abuse and lack any recognized safety for use under medical supervision. Schedule I substances are strictly regulated, and their availability is limited primarily to research purposes. Consequently, this means that they have no currently accepted medical use based on federal law, which directly supports the designation of Schedule I and sets it apart from other schedules that may have accepted medical uses with varying degrees of potential for abuse.

In contrast, the other options imply different levels of medical acceptance or potential for abuse, which does not align with the strict definition of Schedule I.