Controlled Substances 101: What Those Drug Classifications Mean

A plain-language guide to the five “schedules” used by doctors, pharmacists, and law enforcement.

We’ve all seen it—those headlines saying someone was arrested for possession of a C-II drug, or that a warrant was issued for trafficking in a C-I substance. But what exactly do those letters and Roman numerals mean?

Under the federal Controlled Substances Act, drugs and medications are grouped into five categories—called "schedules"—based on two key factors: their potential for abuse and whether they have any accepted medical use. Here's a quick breakdown:

Schedule I (C-I): No Accepted Medical Use
These drugs are considered to have a high potential for abuse and no accepted medical use in the U.S. They are illegal—doctors can't prescribe them, and pharmacies don’t carry them.
Examples: Heroin, LSD, mescaline, peyote.

Schedule II (C-II): Medical Use, Strict Rules
These drugs are legal and do have medical uses, but they also come with a high risk of abuse and dependence. Because of that, they’re tightly regulated—no refills allowed, and every new prescription requires a visit to the doctor.
Examples: Fentanyl (Duragesic), oxycodone (Oxaydo), hydrocodone, methadone (Methadose), hydromorphone (Exalgo ER), morphine, methylphenidate (Daytrana), amphetamines (used for ADHD).

Schedule III (C-III): Moderate Risk
These substances are considered to have a lower risk of abuse than Schedules I or II, but abuse can still lead to dependence—especially psychological.
Examples: Ketamine, Tylenol with codeine, anabolic steroids like testosterone.

Schedule IV (C-IV): Lower Abuse Potential
C-IV drugs are widely used in medicine and are seen as having a relatively low risk of abuse or dependence.
Examples: Lorazepam (Ativan), zolpidem (Ambien), eszopiclone (Lunesta), tramadol (Ultram), phenobarbital (Luminal).

Schedule V (C-V): Lowest Risk
These medications are typically prescribed for mild symptoms like cough or diarrhea and are considered to have the lowest risk of abuse.
Examples: Diphenoxylate with atropine (Lomotil), guaifenesin with codeine (Guaiatussin AC), pregabalin (Lyrica), promethazine with codeine.

So next time you spot “C-II” in a police report or on a prescription label, you’ll know what it means—and why it matters. A drug’s schedule influences how it’s prescribed, dispensed, and enforced, and can make all the difference in a courtroom or a clinic.