How do Buddhists handle mental illness such as depression or bipolar disorder?

How is mental health dealt with by Bhuddists? Is it believed to be a tangible issue e.g. imbalances of chemicals in the brain? Or an issue of the spirit (not sure if spirit is the right word)? Is treatment with western medicine (i.e. antidepressants/mood stabilizers, talk therapy) condemned or accepted? Is there *stigma* surrounding these illnesses like in the western culture? Is depression thought of an extreme form of dukkha or similar? How are hypomania/major depressive episodes handled?
I hope this makes sense, thanks :)