How bad are stimulants (ex.: Ritalin) for someone on the schizophrenic spectrum?

My attention deficit problems have continued to worsen with age, and medication like Ritalin have been recommended. But my doctors aren't so sure, because I've been diagnosed as on the schizophrenic spectrum since youth (one diagnosis says schizotypal, the other SAD, etc), and the effects stimulants can have on them can be questionable at best.