How does one know if diabetes is caused by antipsychotic usage. does it raise blood sugar?

It can: It is thought that most antipsychotics promote Insulin resistance and it may be a function of the same biology that is associated with their therapeutic effect. In any case, there are some antipsychotics like ziprasidone, asenapine, iloperidone an lurasdone that may have less potential for metabolic derangement although it is most likely a matter of degree as opposed to an absolute distinction.

Most of the: Antipsychotic meds that have been associated with diabetes cause significant weight gain.