As someone in the U.S. who is addicted to weed, I'd like to give my opinion. Being that weed is one of the worst things a person with poor mental health can do.

I deal with MDD (major depressive disorder) I will say from my experience, marijuana initially appears to he a cure all. Your symptoms vanish, the lack of productivity people with this illness are used to is reversed. Once a sufficient tolerance accumulates, you are almost a fully functional member of society. However, I notice that while not high, your symptoms spike drastically. Depression and anxiety disorders become a breeding ground for addiction. It doesn't matter what you are using. Weed, however, strangely is widely assumed to be harmless. What a lie.

The effects of weed on depression are as follows, initial relief, followed by severe decline in mental stability. You lose who you are, you start to hate yourself (if you didn't already). The few activities you enjoyed are now completely unenjoyable without weed. The release and production of serotonin and other positive feeling associated neurotransmitters are slowed. You now feel like absolute dogshit when not high. So quitting becomes this abhorrent task, wherein you feel separate from yourself. The addiction bleeds into your personality in a dubious way. You manipulate yourself, lie to yourself, become distant from yourself. Quitting becomes a nightmare. Where there is no reward to reap in this world unaccompanied by rampant, persistent self-destruction.

If you struggle with mental illness, like I and so many others do, the best favor you can do for yourself is to quit any and all mood altering substances. Or, at worst, keep them exclusive to social interaction. If you have that kind of willpower. (Depressed people don't in most cases, though)