The Controlled Substances Act (CSA) places all substances which were in some manner regulated under existing federal law into one of five schedules.  This placement is based upon the substance’s medical use, potential for abuse, and safety or dependence liability.  More information can be found in Title 21 United States Code (USC) Controlled Substances Act.

Alphabetical listing of Controlled Substances

CONTROLLING DRUGS OR OTHER SUBSTANCES THROUGH FORMAL SCHEDULING

The CSA also provides a mechanism for substances to be controlled (added to or transferred between schedules) or decontrolled (removed from control). The procedure for these actions is found in Section 201 of the Act (21U.S.C. §811).
Proceedings to add, delete, or change the schedule of a drug or other substance may be initiated by the Drug Enforcement Administration (DEA), the Department of Health and Human Services (HHS), or by petition from any interested party, including:

• The manufacturer of a drug
• A medical society or association
• A pharmacy association
• A public interest group concerned with drug abuse
• A state or local government agency
• An individual citizen

In determining into which schedule a drug or other substance should be placed, or whether a substance should be decontrolled or rescheduled, certain factors are required to be considered. These factors are listed in Section 201 (c), [21 U.S.C. § 811 (c)] of the CSA as follows:

(1) Its actual or relative potential for abuse.
(2) Scientific evidence of its pharmacological effect, if known.
(3) The state of current scientific knowledge regarding the drug or other substance.
(4) Its history and current pattern of abuse.
(5) The scope, duration, and significance of abuse.
(6) What, if any, risk there is to the public health.
(7) Its psychic or physiological dependence liability.
(8) Whether the substance is an immediate precursor of a substance already controlled under this subchapter.

More information on the Drug Scheduling process 

Federal Drug Trafficking Penalties