source: [ゲーム中毒の女性｜無料GIF画像検索 GIFMAGAZINE 2904407]

a person who is addicted to a particular substance, typically an illegal drug:

(麻薬などの)中毒者, 常用者, 依存者

e.g. a former heroin addict.

with modifier informal an enthusiastic devotee of a specified thing or activity:

｟くだけた話｠ (趣味･娯楽などに対する)熱狂的愛好者, 病みつきな人 (!通例中毒, 愛好対象を示す〖名詞〗の後で)

e.g. a self-confessed chocolate addict

e.g. a must-buy book for the crossword-puzzle addict.

early 20th century: from the obsolete verb addict, which was a back-formation from addicted.