Holy shit >>2 that is the worst evaluation ever. You're on the right track identifying that weed has a placebo affect, but otherwise lol no. Good call there convincing this kid he'd be better off dead.
>>1
Marijuana doesn't make you high all the fucking time unless you find some way to smoke enough so that you are high every waking moment. If you are high every waking moment and feel that you are depressed and sullen about everything when you aren't high, you are addicted. Weed isn't a drug that physically causes or promotes addiction -- I know -- but you are addicted to the euphoria that it provides you, to the point that you believe you can't function without it. No hospital would prescribe marijuana for an addict. You need professional help. Seek it out through school if your parents won't listen.
....if you aren't high every single minute of every day, ignore all that up there! You're still dependent on that high to make life bearable -- this is unhealthy but understandable. This is what leads in to addiction, but not addiction outright. You still need help, but I think you're capable of providing it for yourself.
You say you have no friends, so that's certainly something to be depressed about. That also suggests that you don't have a lot of extracurriculars or activities or things to do. You can probably surf the internet, you can probably watch TV, you can probably play video games, but that isn't enough.
You are depressed because you are bored. Marijuana is an escape from boredom for you. Right now, your biggest activity in life sounds like getting high. You look forward to getting high. You enjoy doing so, maybe less now than before, but you still probably do. Maybe not even because of the affect anymore, but because of the escape it provides you. Well, guess what! Any activity will provide you with the same escape from boredom. Anything you do that preoccupies you will provide you, eventually, with the same feeling.
So, to cure yourself, find something you enjoy or didn't even know you enjoyed and go pursue it! Find something that makes you feel good. Join a school club, go running, watch anime (this is 4ch come on :P ), read, write, read about politics, draw, do something. You're right in saying that marijuana has no realistic place in your future, but a hobby does. Find something that gives you the satisfaction of knowing you've done something neat or productive. It can be something lots of people do, or it can be something no one does -- it just needs to be something.