The study of the human psychism is not yet a science because ther is a lack in a "common" definition of an ordinary mental state and a lack in a "common" description of the ordinary transformations of these states. Psychiatry lists the different disorders (cf DSM 5) but is ther a descritpion of a normal case ?
Freud, Jung and many others decribed the psyschysm with their own model but there is no consensus about these models.
Neurology is best understood with the study of the neurones, the glial cells and their connections.
So it is always difficult to prescribe a medication (derived from the knowledge in neurology) and to apply it in psychiatry (without knowing the principles).
And it is much more dangerous for the multiple therapies based on uncertain models.