As someone with serious depression and mood problems, I can say that cycling is helping. I am notoriously unfocused, although I have an obsessive personality. I have to strike a balance with it.
Hobbies I've been obsessed about:
4x4 Toyota's (lifelong on/off obsession)
R/C Gliders (lifelong on/off obsession)
Robotics (got started... built one small one but obsessed over it for a good week)
Music writing and guitar playing (now its more balanced)
And now... cycling
Does cycling help me mentally? Yes. Do I still need my medication? OH YEAH. There are some things that endorphines and a 'happy feeling' don't fix. Do I think I'll be able to go off my meds if I cycle constantly? No, but I do think I'll be able to decrease my dosage. I had to double it last year because of stress and noticing that I was lagging between doses. I hope to eliminate that part.
However at 315lbs, I can't lose enough weight. That is the reason I started cycling. My cycling buddy is getting over a divorce and trying to be less introverted and more outgoing. Its helping both of us!
In other words, you can't lose.