Have you ever watched the news? We have many highly publicized examples of rich people being addicted to drugs.

For fiction, I like the approach they took on the tv show House. Maybe not rich but certainly privileged enough to get away with an addiction that would have ruined anyone else’s life.

But maybe a good approach to your story is to imagine an unusual dealer:: a wealthy person is not visiting the neighborhood crack house. For example Michael Jackson’s addiction was fed by an actual doctor authorized to write prescriptions so his drugs were “legal”