Precursor chemicals are used to make certain drugs, whether prescription, over-the-counter, or controlled substances. Illegal drugs like heroin and cocaine are made from precursor chemicals. The Drug Enforcement Agency (DEA) restricts the import and sale of the chemicals required to make illicit drugs in an effort to minimize the production of such drugs.

The United Nations (UN) also attempts to regulate the sale and control of these precursor chemicals. In 1988, the UN convened in an effort to control drug trafficking around the globe. Members of the UN agreed to impose restrictions on the import, export, production and possession of precursors. Most countries in the UN have their own requirements for licensing to handle these chemicals in a legal fashion—and criminal penalties for those who do so illegally.

The UN has listed several precursors as chemicals of concern, dividing them into two Tables. Table 1 contains precursor chemicals that are “most critical” to making drugs, while Table 2 includes precursors that are less critical and therefore less regulated. 

The DEA calls these chemicals List I and List II precursors. Precursors in List I include chemicals like ergotamine (which can be used to make LSD) and more tame chemicals like iodine. List II includes precursors such as acetone which is used to make ecstasy.