Medicines and prescriptions
What Is a Controlled Substance? Why Labels Say 'CII'
Controlled substance · say it: kun-TROHLD SUB-stunssAlso written: controlled drug, scheduled drug, Schedule II, CD
Short answer
A controlled substance is a medicine or drug whose making, prescribing and supply are tightly regulated by law because it can be misused or cause dependence.
What it means
A controlled substance is a medicine or drug that the law regulates more strictly than usual, because it can be misused, lead to addiction or cause dependence. Examples include opioid painkillers, benzodiazepines, ADHD stimulants and some sleep medicines. In the US they are placed in 'schedules' (I to V); other countries use their own classes.
Labels and packs show this with a symbol or phrase such as 'CII' or 'Controlled Drug'. It explains the extra rules: prescriptions may need special forms, refills can be limited, and pharmacies keep extra records. Labels also warn about misuse, addiction and physical dependence, about keeping the medicine locked away, and about never sharing it, which is illegal.
Physical dependence is not the same as addiction. Dependence means the body has adjusted and withdrawal can happen if stopped suddenly; addiction is compulsive use despite harm.
Where you may see it
- The 'Drug abuse and dependence' section of prescribing information
- 'C-II' to 'C-V' symbols on US prescription packs and labels
- Pharmacy prescription records
📄 How it looks on a report
CII. Contains oxycodone, a Schedule II controlled substance with a high potential for abuse.
🙅 What it does not mean
- Being prescribed a controlled substance does not mean your doctor thinks you will misuse it.
- It does not mean the medicine is illegal to take when it is prescribed for you.
- A lower schedule does not mean it is free of risk.
🎯 Check yourself
Which of these is the right meaning of “Controlled substance”?
🗒️ Questions to ask your doctor
🧾 Reports where you will see “Controlled substance”
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💊 Medicines whose labels mention “Controlled substance”
Plain-English explanations of each medicine, from its official FDA label.
- Alprazolam
a benzodiazepine, a type of central nervous system medicine
- Clonazepam
a benzodiazepine, a type of medicine that slows activity in the central nervous system
- Diazepam
A benzodiazepine, a type of medicine that slows activity in the central nervous system (brain and spinal cord)
- Lorazepam
A benzodiazepine, a type of anxiety medicine
- Tramadol
an opioid pain medicine, also called an opioid analgesic
- Zolpidem Tartrate
a sleep medicine of the imidazopyridine class. The label describes it as a GABA A receptor positive modulator.
🔗 Read more from trusted sources
- “Controlled substance” on MedlinePlus ↗
US National Library of Medicine
- NCI Dictionary definition ↗
US National Cancer Institute: “controlled substance”
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