Unfair treatment from parents

I am un-happy living at home with the rules that have been implied. Even when I do nothing wrong, I still feel as if they blame me. I do everything in the home for chores helping my parents and errands. I have other siblings as well but the do not help. I am getting emotionally depressed and want to start doing drugs and staying out the house because once coming home I cry most the time. I feel as if my parents don't understand me yet. I try to make them time after time. I have started trying to tell them I am moving out and they react as if I am doing something horrible and hit and yell abuse at me. Everyday it's the same thing. I want to be gone but my family won't let me. Do I leave with out their permission? What do I do? Please help. I am only 20 years old. I do have a friend's house who is willing to let me stay with her as long as I can. I can't focus on my studies any more at all as well. Please help.