Most of the studies linking marijuana to higher rates of schizophrenia can be explained by the opposite relationship. That is, individuals with schizophrenia may be more likely to use cannabis because it helps them in some way or another.
Likewise, there is evidence that supports marijuana as a treatment for schizophrenia. For example, studies have linked marijuana use to better cognitive performance among schizophrenics.
Also, a clinical trial involving 39 schizophrenia patients compared cannabidiol (CBD), a compound found in marijuana, with a commonly prescribed antipsychotic, amisulpride, and found treatment with cannabidiol resulted in superior outcomes.