illegal drug
Refers to substances prohibited by law, such as narcotics or controlled substances. Often used in legal or news contexts.
He was arrested for possession of illegal drugs.
Using illegal drugs harms your health.
違法薬物 is the precise legal/bureaucratic term for illegal substances, while ドラッグ is the more colloquial word used in casual speech and news headlines.
Compound of 違法 (illegal) and 薬物 (drug). The term is a straightforward modern coinage.