In the United States, the schedule of a controlled substance indicates how tightly regulated a substance is based on accepted medical use and its potential for abuse or dependence, according to the Drug Enforcement Administration. Schedule I drugs are the most highly regulated, while Schedule V drugs are the least regulated.
Schedule I substances are those that have no accepted medical use and a high potential for abuse, reports the DEA. Heroin, marijuana, Ecstasy and LSD are considered Schedule I drugs. Drugs in Schedules II through Schedule V have an accepted medical use, but a high risk for dependence or abuse. Schedule II drugs have a high potential for physical or psychological dependence and include narcotic drugs, such as fentanyl, methadone and morphine, and non-narcotic drugs, like amphetamines or methylphenidate.
Schedule III drugs have a lower risk of physical dependence, but still have a high risk of psychological dependence, claims the DEA. Drugs with lower levels of narcotic medications such as acetaminophen with codeine and non-narcotic drugs like anabolic steroids fall into this category. Schedules IV and V drugs have a low risk of either physical or psychological dependence. Benzodiazepines and cough syrups containing small amounts of narcotic drugs fall into these categories.