heroin / heroine are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
heroin: (noun) a narcotic that is considered a hard drug; a highly addictive morphine derivative; intravenous injection provides the fastest and most intense rush.
heroine: (noun) the main good female character in a work of fiction. (noun) a woman possessing heroic qualities or a woman who has performed heroic deeds.
heroin: hh·EH·r·ow·ah·n
heroine: hh·EH·r·ow·ah·n
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)