One point is that the causal chain should largely be reversed when we look at the relation between biological phenomena and different psychological ailments. Treating the chemicals should be considered mostly treating symptoms. Unfortunately, many children today are over medicated because doctors think that if they've removed the symptom (i.e. ADD) they've fixed the problem.

Second, we should look at what the soul needs. For example, if the soul is a separate, higher substance it will not be satiated by a lower substance. As Jesus says, "man does not live by bread alone." The only thing at the level of a soul is another soul. So, souls need relationships with other souls. Theology also comes into the picture here, since theology claims the only thing higher than a human soul is God. So, ultimate satiation for our soul is found in God. The medieval church has extensive experience and spiritual disciplines aimed at connecting our souls to God. Thus, theology becomes an important aspect of psychology.