What Is a Controlled Substance?

Hydrocodone capsules, a schedule III drug, spilling out of a prescription bottle

 Moussa81 / Getty Images

Controlled substances are illegal or prescription drugs regulated by the Controlled Substances Act (CSA) in the United States. Recognizing the potential that certain medications have for misuse and dependence, Congress enacted the CSA as part of the Comprehensive Drug Abuse Prevention and Control Act of 1970.

This act categorizes all substances that are regulated under federal law into “schedules,” depending on how potentially dangerous they are. The schedule the drug is placed under depends on its medical use, its potential for abuse, and its safety or how easily people become dependent on it.

Careful consideration has gone into this categorization. The control of drugs through law exists to protect people from the harm that these drugs can do. It is based on research from many different sources into the potential harmfulness of the drug, both to individuals and to society.

The five schedules of drugs should not be confused with the five classes of drugs, a different way of organizing drugs according to their main properties. The five classes of drugs are narcotics, depressants, stimulants, hallucinogens, and anabolic steroids.

This article discusses each of the five schedules of controlled substances and the different substances found under each classification. It also covers what you need to know if your doctor prescribes a controlled substance.

Schedule 1 Drugs

Schedule I drugs (the law uses Roman numerals one through five) have a high potential for abuse. They currently have no federally accepted medical use in treatment in the U.S., and there is a lack of accepted safety for use of the drug or substance under medical supervision.

Examples of Schedule I substances include:

  • Gamma-hydroxybutyric acid (GHB)
  • Heroin
  • Lysergic acid diethylamide (LSD)
  • Methaqualone

Marijuana is the only Schedule I drug that is legal for medicinal and recreational uses in many states. However, many experts believe the drug's status should be changed to allow for more comprehensive studies to determine the medical benefits of marijuana.

Schedule 2 Drugs

Schedule II drugs and substances also have a high potential for abuse. They differ from Schedule I drugs in that they do have a currently accepted medical use in treatment in the U.S. or a currently accepted medical use with severe restrictions.

Examples of Schedule II substances include:

Abuse of schedule II drugs may lead to severe psychological or physical dependence.

Schedule 3 Drugs

Schedule III drugs and substances have less potential for abuse than the drugs or substances in Schedules I and II. They have a currently accepted medical use in treatment in the U.S.

Abuse of the drug or substance may lead to moderate or low physical dependence or high psychological dependence.

Examples of Schedule III substances include:

Schedule 4 Drugs

These drugs and substances have a low potential for abuse relative to those in Schedule III. The drug or substance has a currently accepted medical use in treatment in the United States.

Abuse of the drug or other substance may lead to limited physical dependence or psychological dependence relative to the drugs or other substances in Schedule III.

Examples of Schedule IV substances include:

Schedule 5 Drugs

The drug or substance has a low potential for abuse relative to those in Schedule IV. The drug or other substance has a currently accepted medical use in treatment in the United States.

Abuse of the drug or other substances may lead to limited physical dependence or psychological dependence relative to the drugs or other substances in Schedule IV. Schedule V drugs include cough medicines with codeine.


Controlled substances are classified into schedules based on their medical value and potential for abuse. Schedule 1 drugs have no federally recognized medical purpose and high risk for dependence and abuse. Schedule 2 drugs may have some purpose in restricted medical settings. Schedules 3 have a lower risk for dependence and may be prescribed for medical treatment. Schedule 4 and 5 drugs have a lower potential for abuse.

If Your Doctor Prescribes a Controlled Substance

While not all prescription drugs are controlled, there are several (for example, opioid pain medications) that do fall under the category of controlled substances. If your doctor prescribes one of these drugs, it's essential that you only take it as directed.

In addition to having limited refills, you may need to sign a pain medication agreement, or a contract between you and the doctor to ensure that you're taking the drugs exactly as prescribed.

While the details can vary from doctor to doctor, the contract may also ask you to agree to:

  • Get your prescription from only one pharmacy
  • Not request or take pain medications from another provider
  • Submit to random drug testing

If you or a loved one are struggling with substance use or addiction, contact the Substance Abuse and Mental Health Services Administration (SAMHSA) National Helpline at 1-800-662-4357 for information on support and treatment facilities in your area.

For more mental health resources, see our National Helpline Database.

A Word From Verywell

There are times that your doctor may prescribe a controlled substance to treat a health condition. You should always discuss proper dosage and administration with your doctor. Carefully following the instructions can help minimize the risks of taking a controlled substance for the treatment of a health condition.

Frequently Asked Questions

  • What is a controlled substance?

    A controlled substance is any drug or chemical that has its possession, use, or manufacture regulated by the government. These substances are regulated due to their potential for misuse, abuse, or addiction.

  • What’s the difference between schedules of drugs and classes of drugs?

    Schedules of drugs refer to how a drug is regulated by the U.S. government. Classes of drugs refer to the main properties of a substance and how it affects the body.

  • Which schedule of drugs require a prescription?

    Schedule 3, Schedule 4, and Schedule 5 drugs are available for use with a prescription. Schedule 2 drugs may be used in medical settings with extreme restrictions. Schedule 1 drugs, however, do not have any accepted medical use and cannot be acquired with a prescription.

3 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Gabay M. The federal Controlled Substances Act: Schedules and pharmacy registrationHosp Pharm. 2013;48(6):473-474. doi:10.1310/hpj4806-473

  2. Corroon J, Kight R. Regulatory status of cannabidiol in the United States: A perspective. Cannabis Cannabinoid Res. 2018;3(1):190-194. doi:10.1089/can.2018.0030

  3. U.S. Drug Enforcement Administration. The Controlled Substances Act.

Additional Reading

By Elizabeth Hartney, BSc, MSc, MA, PhD
Elizabeth Hartney, BSc, MSc, MA, PhD is a psychologist, professor, and Director of the Centre for Health Leadership and Research at Royal Roads University, Canada.