My hypothesis is that exercise-as-such helps with mood disorders, exercise outdoors (to regulate circadian rhythms) helps more, and exercise with someone else (to have pleasant social interaction and a reality check on one's thinking during conversation) helps still more. I wouldn't recommend NOT taking standard medications--I've seen a lot of people get a lot of help from lithium, but lithium leads to weight gain for many people, so then the exercise becomes all the more necessary.