Is it ok to take antipsychotics and pot?

My son has recently come out of psychosis and diagnosed Bipolar 1. He is taking medications though during this past week I have noticed he's started smoking pot again, he gave this up around 7 months ago. I have lectured him about it though he appears happier than he has been in months. I just want to know is it really bad for him to do this being bipolar and mixed with antipyschotics?does it help some people with bipolar? would he need it because he's going through something? or will it make him worse off? Thanks.