also: ジャンキ
noun
Refers specifically to a person addicted to drugs, matching the original English 'junkie'. Often used in contexts of substance abuse.
彼は若い頃、ジャンキーだったが、今は更生している。
He was a junkie when he was young, but now he's rehabilitated.
noun
Extended use for someone obsessed with a particular activity or thing, such as a 'fitness junkie' or 'news junkie'. Colloquial and often used in compound-like expressions.
彼女は完全なフィットネスジャンキーで、毎日ジムに通っている。
She's a total fitness junkie and goes to the gym every day.