Marijuana does not cause mental disorder, but if you have a pre-disposition for mental illness (or have a mental illness that hasn't shown itself yet such as Schizophrenia; which usually develops in the early to mid-20s of males) then yes, Marijuana like other psychedelics can cause this disorder to surface. If you have the disorder, it is almost certain that you will develop at some later point of great mental stress.

Also, Schizophrenia is in no way related to Dissociative Identity Disorder (the official name of "Mutliple Personalities" and/or "Split Personalities." It just so happens that many mental disorders have the same common themes/symptoms (DID, Schizophrenia, PTSD, etc) and can be confused with each other.