An illegal drug is

• A. A safe for medical use
• B. A chemical substance that cannot be lawfully manufactured, possessed, bought, or sold
• C. Used in hospitals
• D. Legal in some countries

Answer: (B)

Legality and regulation determine whether a substance is an illegal drug: it is a chemical substance that cannot be lawfully manufactured, possessed, bought, or sold. This definition emphasizes the legal status—without the proper authorization, licensing, or prescription, these actions are prohibited. Some drugs may have legitimate medical uses or be used in hospitals under supervision, and certain countries may allow or regulate them differently, but the core idea of an illegal drug is that the law forbids production, possession, purchase, or sale without special authorization. The other statements describe contexts where a drug might be used legally or safely, or that it’s used somewhere, but they don’t capture the essential concept of illegality.