Definition of Controlled Substance Schedules Under the Controlled Substances Act
Drugs and other substances that are considered controlled substances under the Controlled Substances Act (CSA) are divided into five schedules. An updated and complete list of the schedules is published annually in Title 21 Code of Federal Regulations (C.F.R.) §§ 1308.11 through 1308.15. Substances are placed in their respective schedules based on whether they have a currently accepted medical use in treatment in the United States, their relative abuse potential, and the likelihood of causing dependence when abused.
Please take a look at the DEA website for explanation of the schedules and a list of 19 pages of controlled substances along with their schedule listing (CSA SCH): DEA, Drug Scheduling
Here is an updated link to the Diversion Control Division of the DEA with more detail on the drug schedules: Diversion Control Division, Controlled Substance Schedules