adult paperback (fiction) about a female addict

Hello, I am looking to find a paperback novel that I read in 1976. The novel was bought in Montreal and might have been a couple of years old at the time. It portrayed a young girl who delves into the world of drugs while living in the city. Eventually, she gets hooked on heroin. It was written for mature adults, relatively explicit if I remember correctly.
I remember that her last name was Fitzgerald, she was the main character. She started off by buying cough syrup at the pharmacy with a female friend of hers at the age of 14 or 15. Things progress from there until she gets hooked on heroin. I believe the story was told in the first person.
I would very much like to find this book and read it once again. It was among one of the first adult books that I remember reading and her story and her world left quite an impression on me. * by adult book, I mean a novel that was written for an adult audience... not one of those triple X trashy ones!

Not sure if the timing fits, but maybe The Autobiography of Christiane F ? Admittedly, she was in Berlin, so probably not named Fitzgerald, but thought it worth mentioning.

>2 Caramellunacy: Good try! I am familiar with Christiane F's story as well. Very similar indeed. Thanks for trying, hopefully something turns up...