I saw this movie 3-4 years ago on NetFlix. A woman is standing on roof edge ready to jump, and a friend gives her drugs. Eventually she runs out of money, and pays a drug dealer with oral sex. One day, tiring of the oral sex, she pulls out a gun to steal the drugs, fights with the drug dealer, and kills him and his accomplice. When detectives later arrive at her apartment, they find that she has gone mad and decapitated her friend (who really never was that nice anyway). I think a dog was drinking the blood.
I cannot remember any names of the actors.