The Controlled Substances Act of 1970 divided substances to be regulated into 5 schedules. These schedules govern the legal distribution and use of most substances with a significant abuse liability. The Drug Enforcement Administration is the primary federal agency charged with enforcing these regulations and with coordinating national and international efforts to reduce illicit drug supply. Hence, this classification scheme is often refereed to as the DEA Schedules.

Schedule I substances have a high abuse liability and no approved medical use. These substances are available for investigational purposes only, and the research protocol must be approved by the Food and Drug Administration (FDA) prior to granting a license for handling Schedule I compounds. Drugs are provided by manufactures under federal contract. Pharmacies do not sell these compounds nor can physicians write prescriptions for them. Special record-keeping and storage procedures are required for all Schedule I substances.

Schedule II-IV substances have decreasing abuse liabilities (II is the highest) and approved medical uses. Physicians are licensed to prescribe these compounds and pharmacies can dispense them, although pharmacies do not stock all of these substances. Schedule II compounds have more stringent record-keeping and storage requirements than do Schedule III and IV substances.

Schedule V substances have a recognized abuse liability (and approved medical uses) but are generally not regulated (eg: they are available without prescription). Many of these substances are used in common, over-the-counter medicines. Including compounds on this schedule facilitates state and local regulations deemed appropriate in some jurisdictions (eg: An individual state may impose restrictions on some substance considered to have an unexpectedly high abuse liability).