addict

(noun) someone who is so ardently devoted to something that it resembles an addiction. Synonyms: nut, freak, junkie, junky. Examples: "A golf addict." "A car nut." "A bodybuilding freak." "A news junkie."

(noun) someone who is physiologically dependent on a substance; abrupt deprivation of the substance produces withdrawal symptoms.

(verb) to cause (someone or oneself) to become dependent (on something, especially a narcotic drug). Synonyms: hook.