Most drugs that require a prescription from a doctor are not controlled substances. The Controlled Substances Act and its implementing regulations, however, assign certain substances to one of five "schedules." These substances are placed in a schedule based on their potential for abuse, which may lead to physical or psychological dependency. Schedule I substances have no accepted medical use for treatment in the United States and are not available by prescription. Schedule II through V substances have accepted medical use and varying potentials for abuse and dependency. Practitioners (e.g., doctors, dentists, veterinarians, physician assistants, advance practice nurses) who are licensed by a State and registered with DEA may prescribe these substances. Controlled substances include narcotics (pain relievers), stimulants, depressants, hallucinogens, and anabolic steroids. A complete list of controlled substances can be found in Title 21 of the Code of Federal Examples of controlled substances are shown below.

Schedule I
Heroin, marijuana, mescaline, methcathinone.

Schedule II
Amphetamine, codeine, fentanyl, oxycodone,Hydromorphone, meperidine, methadone, Methylphenidate (Ritalin), morphine, pentobarbital, phencyclidine,(PCP), secobarbital

Schedule III
Anabolic steroids, phendimetrazine, and products that contain small quantities ofcertain schedule II controlled substances,such as codeine, in combination with noncontrolled ingredients, such as aspirin.

Schedule IV
Alprazolam (Xanax), chlordiazepoxide (Librium), diazepam (Valium), lorazepam(Ativan), phenobarbital, phentermine.

Schedule V
Buprenorphine and many cough Preparations that contain a limited amount of codeine.