Does a doctor need permission for both divorced parents to treat a child with medication?

My ex son in law doesn't want my grand daughter on risperidal and he has taken her off the med and filed court papers and sent them to her doctors saying the doc can not treat her with out his permission. Can her really do that? My daughter has custodial care of my granddaughter and has been taking her to the doctor for post traumatic stress disorder. What can be done?