Which classification is generally the most restricted of controlled substances?

The classification that is generally the most restricted of controlled substances is Schedule I. This categorization reflects substances that have a high potential for abuse and do not have accepted medical use in the United States. Consequently, these substances are subject to the strictest regulations and controls.

Substances classified as Schedule I cannot be prescribed, and possession or distribution is prohibited, making them exceptionally restricted in comparison to those in other schedules. This is in stark contrast to Schedule II, which, while also highly regulated and risky, can still be prescribed under strict circumstances for legitimate medical reasons. Schedule III and Schedule IV substances have progressively lower potential for abuse and more accepted medical uses, leading to less stringent regulatory requirements.

Schedule I includes drugs such as heroin and LSD that are deemed to have no accepted medical use, highlighting the rationale behind their complete prohibition.