Drugs such as cocaine, marijuana, heroin, and others are considered to be illicit drugs. Those being drugs that are illegal.
An illicit drug is an illegal drug.
drug (n.) A substance used in the diagnosis, treatment, or prevention of a disease or as a component of a medication. drug (n.) A chemical substance, such as a narcotic or hallucinogen, that affects...
Using drugs/medicine for purposes other than for health benefits and when they haven't been prescribed to you.