Marijuana can be good medicine, however I'm not sure how good it is for someone w m.i.
When my sz husband smoked pot, he was calm, slept well and was generally in a good mood. But when the pot ran out, all of his symptoms of anger, paranoia, etc., came back ten-fold. It was a horrible rebound effect when he no longer had pot. The agitation would last a few days, then he'd be back to his usual Sz state.
So, I think for his mental stability, pot is probably not recommended.
I strongly discourage using the synthetic marijuana that you could buy legally. It's potentially really dangerous for anyone, especially someone who has a m.i.