What is a controlled substance?

A controlled substance is a drug or other substance that the United States government has placed in one of five lists, called schedules, under the Controlled Substances Act. Federal law defines the term in 21 U.S.C. 802(6) as a drug or other substance, or immediate precursor, included in schedule I, II, III, IV or V. If a drug is not on one of those lists, it is not a federally controlled substance. Gabapentin, trazodone, cyclobenzaprine and hydroxyzine are examples: none of them appears on the DEA list dated August 27, 2026.

The United Kingdom works differently. There, a drug is a controlled drug when it is listed in Schedule 2 to the Misuse of Drugs Act 1971, which sorts drugs into Class A, B and C. A second law, the Misuse of Drugs Regulations 2001, groups the same drugs into Schedules 1 to 5 according to how they may be produced, supplied, prescribed and possessed. Both are covered below.

What is the Controlled Substances Act?

The Controlled Substances Act (CSA) is title II of the Comprehensive Drug Abuse Prevention and Control Act of 1970 (Public Law 91-513). The US Code prints it as 21 U.S.C. 801 and the sections that follow. The first of its congressional findings says that many of the drugs it covers "have a useful and legitimate medical purpose and are necessary to maintain the health and general welfare of the American people." That sentence explains why most controlled substances are also medicines. The law sets conditions for making, distributing, prescribing, dispensing and possessing them.

The detailed rules are in Title 21 of the Code of Federal Regulations. Part 1308 prints the current schedules, and part 1306 sets the rules for prescriptions. The Drug Enforcement Administration (DEA) publishes an alphabetical list of every scheduled substance with its Controlled Substances Code Number (CSCN), the four-digit identifier used throughout this site. The edition we used is dated August 27, 2026.

What are the five drug schedules?

Section 812 of the CSA establishes five schedules, numbered I to V. Placement depends on three findings that Congress wrote into section 812(b): how likely the substance is to be abused, whether it has an accepted medical use in the United States, and what kind of dependence it may cause. The wording below is taken from 21 U.S.C. 812(b).

The numbers rank the statutory criteria. They do not measure how risky a particular drug is for a particular person. The page Drug schedules explained goes through each schedule with examples from the DEA list and the prescription rules that attach to it.

Who decides which drugs are controlled?

Section 811 of the CSA gives the power to add, transfer or remove a substance to the Attorney General, who acts by rule on the record after an opportunity for a hearing. The regulations in 21 CFR part 1308 name the DEA Administrator as the official who receives petitions and starts proceedings. A proceeding can begin with the Attorney General, with the Secretary of Health and Human Services (HHS), or with any interested party.

HHS has a binding role. Under 21 U.S.C. 811(b), the Secretary's scientific and medical recommendations are binding on the Attorney General, and if the Secretary recommends that a drug not be controlled, the Attorney General cannot control it. The DEA rule on petitions, 21 CFR 1308.43(d), repeats this and requires the DEA to request the HHS evaluation before it starts a rulemaking. Changes are published in the Federal Register and then appear in the schedules in 21 CFR part 1308. Section 812(a) also says the schedules are to be updated and republished on an annual basis.

Is alcohol a controlled substance?

No. The definition of controlled substance in 21 U.S.C. 802(6) says the term "does not include distilled spirits, wine, malt beverages, or tobacco," as those are defined in the Internal Revenue Code. Alcohol and tobacco are regulated under other laws and have no schedule number. The schedules page answers the question "what schedule is alcohol" in more detail.

Federal law and state law

The CSA is a federal statute, and states have their own controlled substances laws. Section 903 of the CSA says Congress did not intend to occupy the whole field to the exclusion of state law on the same subject, unless there is a "positive conflict" between the two. In practice a state can add a substance to its own lists, set its own penalties, or add rules for prescribing.

That is why a drug can be controlled in one state and not at the federal level. We have not opened any state statute for this page, so we do not list individual states. The authority for your state is its legislature and its board of pharmacy. If you need to know whether a drug has an extra state control, ask your pharmacist or check the board's website.

What is the UK equivalent?

The Misuse of Drugs Act 1971 is the British counterpart. Its Schedule 2 lists controlled drugs in three parts: Part I is Class A, Part II is Class B and Part III is Class C. The class sets the maximum criminal penalty. The Misuse of Drugs Regulations 2001 add five schedules that deal with lawful production, supply, prescribing and possession. A drug can therefore carry two labels at once, for example "Class C, Schedule 3" for tramadol.

The two countries do not use the same numbers for the same thing. A US Schedule IV drug is not the same as a UK Schedule 4 drug, and US Schedule II is not UK Class B. Penalty bands from gov.uk and the rest of the British system are on UK drug classes.

The 18 drugs on this site

The table gives the status of each drug we cover. US schedules and CSCN codes come from the DEA alphabetical list of August 27, 2026. UK classes and schedules come from the Home Office list of the most commonly encountered controlled drugs, updated April 1, 2025. That list is not exhaustive, so "not on the Home Office list" means only that the drug does not appear there. Each name links to a page with more detail.

Three entries need a comment. Amphetamine is Class B in the UK, but the Home Office list carries a note: it becomes Class A when it is in a preparation designed for administration by injection. Fentanyl is the only drug in the table that is Class A without that condition. The Home Office list spells lisdexamfetamine as "lisdexamphetamine" and shows it as Class B, Schedule 2.

What does controlled status mean for a patient?

For a person who takes a prescribed medicine, the main practical effect of a schedule is on the prescription. Federal rules prohibit refilling a Schedule II prescription, and Schedule III and IV prescriptions cannot be filled or refilled more than six months after issue, or refilled more than five times. The exact regulation numbers are on the schedules page. A controlled status says which legal rules apply to a drug. It does not say how a given person will respond to it.

This site gives legal and regulatory information taken from official texts. It is not medical or legal advice. If you have a question about your own medicine, ask your prescriber or pharmacist. See how we work for our sources and the legal notice.

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