Most prisons do at least some sort of mental health evaluation when during the intake process. While incarcerated, he should have a counselor (classification officer maybe) who is in charge of overseeing his case. He should address this issue with the counselor. He can also request one through the prison medical staff. If this is of no avail, I ussgest you surf the net a little and find a prison watchdog group who is active in the state - they will be able to advise you what additional steps that can be taken to get the evaluation done. Once the evalutaion is completed, if it is determined he needs medication, the prison medical staff will dispense the medication as prescribed at no cost.
------------------
Please note that these comments do not constitute legal advice. It is always recommended that you consult with a local attorney, who can explore all the facts and issues of your specific situation and then advise you of any legal rights and remedies you may have under the current laws of your jurisdiction.