Before I read Robert Aitken's, "The Path of Zen," diving into ancient Sutras, and finally joining the Sangha, I was a very cynical and intellectually driven man. The human mind has always fascinated me (probably stemming from trying to understand myself initially) and psychology was the only study in college that called to me. I learned a lot from all the classes, but I always sensed that something critical was missing. Practicing Zen, I uncovered these missing pieces.
Psychology has gotten a bit more light-hearted over the years, with the introduction of Positive Psychology and other schools, but many perspectives still paint the individual as a victim who has no choice regarding who they are. Whether who we are is influenced by our genes, conditioning or other environmental aspects, we are subject to our rigid psyches. That... is... nonsense. Psychologists attempt to ease the suffering of others through therapy and medication, but they fail to see and express the root causes of suffering and dissatisfaction in general. Clients could really benefit from study, discourse and meditation instead. They convince people that there is something "wrong" with them, that the behavior and underlying thoughts must be "corrected." This presents some kind of future ideal of who a person will be, rather than working with the here and now.
Present moment awareness, the Four Noble Truths, the Three Marks of Existence, the Eightfold Path and the Twelve Links of Dependent Origination fit snug with psychology and if implemented in the mental health field they could benefit many. To sum it up, Dukkha is the root of determining mental health.