ZBomber - I don't think this is about the drug itself, like Don_Diego said it's an autobiographical song. Stevie said that she wrote it when she was first getting really famous, and she was becoming thin and having a tough time in as many words. I think it's a reference that music is like Bella Donna, because at the time it was killing her but she was so addicted to making it.
This is the first song I ever heard by Stevie solo, and I adored it. The vocals in this song are so intensely passionate and the lyrics are really profound.