The Controlled Substances Act (CSA) was passed in 1970 by the Congress of Richard Nixon and soon after signed into law. Under the terms of the CSA, the Food and Drug Administration (FDA) and the Drug Enforcement Agency (DEA) would be responsible for classifying drugs into one of five categories called “schedules” based on their supposed abuse potential or known medical applications. In theory, Schedule I drugs have the highest abuse potential with no medical purpose. They also carry the heaviest penalties associated with their use or possession. Schedule V drugs, on the other end of the spectrum, have medical applications but also have a low abuse potential.

The CSA has been amended several times. One major amendment was introduced in 2000, the Hillory J. Farias and Samantha Reid Date-Rape Drug Prohibition Act. Under this amendment, gamma-hydroxybutyric acid (GHB) was placed into Schedule I, and sodium oxybate was placed into Schedule III.

Schedule I drugs

Drugs with high abuse potential that have no known medical use. Currently, the drugs listed under Schedule I include:

Alpha-methyltryptamine (a-MT)
BZP
Cathinone
DMT
Etorphine
GHB
Heroin
Ibogaine
LSD
Marijuana
MDMA
Mescaline
Methaqualone
Peyote
Psilocybin
Psilocin

Historically, the scheduling of many of these controlled substances is subject more to political whims rather than to scientific principles. Several studies have been published demonstrating a significant clinical benefit of many Schedule I drugs.

Schedule II drugs

These drugs have a high potential for abuse, but also have a documented medical application. These drugs may only be distributed under prescription or in case of an emergency. These drugs include:

Amphetamines
Barbiturates
Cocaine
Codeine
Diphenoxylate
Fentanyl
Hydrocodone
Hydromorphone
Methadone
Methamphetamine
Methylphenidate
Morphine
Nabilone
Opium tincture
Oxycodone
Oxymorphone
Nembutal
Pethidine
Phencyclidine
Secobarbital
Tapentadol

Schedule III drugs

Drugs classified under Schedule III have a lower abuse potential than Schedule I or Schedule II drugs. They have a medically identified purpose, but may still produce a form of dependence if used improperly. They currently include:

Anabolic steroids
Barbiturates with an intermediate time course of action (talbutal or butalbital)
Benzphetamine HCl
Buprenorphine
Dihydrocodeine when compounded with other substances, to a certain dosage and concentration.
Ergine
Ketamine
Marinol
Paregoric
Phendimetrazine Tartrate
Vicodin

Schedule IV drugs

Schedule IV drugs generally have low abuse potential, and have a use in the clinical setting. There is a risk of dependence, but this may depend on use of drugs that are schedule III or up. Some schedule IV drugs include:

Benzodiazepines (Xanax, valium)
Carisoprodol
Chloral hydrate
Modafinil
Phenobarbital
Tramadol

Schedule V drugs

As with above, schedule V drugs are those with low abuse potential and a clinical use. These drugs may lead to dependence if abused. Some schedule V drugs are listed below:

Anticonvulsants such as pregabalin
Antidiarrheal drugs (some are psychoactive)
Promethazine + codeine as a cough suppressant