I like the Alison Lohman guess. She was the star of the movie. Macaulay Culkin born became famous overnight with the role of Kevin in Home Alone. I know she's married with a kid now, but she fits the description fairly well, no? I'm not that familiar with most of his films, so I don't know if he ever played a drug addict. Enty may not have meant that as a clue, but people will just subconsciously use language without realizing they're leaking.
Private School the movie with the sex scene.
Kourtney Kardashian shows off her naked ass - see picture here! Thought of Maggie Gyllenhaal because of her brother's name she won't have trouble being a B-lister again and she has talent but she is also steadily working. But maybe that's not the film in question. I loved her in that. Sometimes you get lucky - like the homeless guy skate John Economou.