There is no magic #!
Like most categories of medications, psych meds are available to treat a plethora of diseases, disorders, etc.
approved or used "off label", it's common to try different meds until you find the right one, or combo. I have seen patients on 2 meds at the same time, treating the same thing. If you have several issues, you may need several meds. There is no limit but interactions go up w/ each med.