any substance having psychological effects, such as a narcotic, stimulant, or hallucinogenic agent, especially habit-forming and addictive substances, sold or used illegally;
as, a drug habit; a drug treatment program; a teenager into drugs; a drug bust; addicted to drugs; high on drugs.
“They [smaller and poorer nations] have lined up to recount how drug trafficking and consumption have corrupted their struggling economies and societies and why they are hard pressed to stop it.”
— Christopher S. Wren (N Y. Times, June 10, 1998, p. A5)