The Controlled Substances Act was passed in 1970 and designed to regulate the importation, manufacture, distribution, and possession of substances that were designated as potential substances of abuse. The act basically assigned the duties of identifying controlled substances to the United States Drug Enforcement Administration (DEA) and the Food and Drug Administration (FDA).
Those substances classified in the Schedule I category are deemed to have no known medicinal purposes in the United States and can only be acquired with special permissions from the government. These substances are typically used in research or are well-known illicit drugs. The best-known opiate substance in the Schedule I category is heroin.
Schedules II through V can legally be prescribed by a physician and are subject to various levels of control by the government. A substance categorized higher up in the hierarchy (e.g., Schedule II) is considered to be potentially more dangerous and addictive than those categorized at the lower levels.
Despite some of the misinformation on the Internet, all opiate drugs (both those used medicinally and opiate drugs that are not used medicinally) are classified as controlled substances unless a specific formulation of an opiate substance is in development and has not yet been registered with the government, or it is manufactured illegally and has a different chemical makeup that distinguishes it as a completely different opiate from the recognized opiate drugs.
It should be noted that codeine is one of the opiates that can be found at several levels of classification of controlled substances, depending on its chemical form and the amount of codeine in the particular substance. For instance: