IMO, it really depends on the cause of the psychosis; if its secondary to a medical problem like a thyroid disorder which has been treated properly then the risk of subsequent psychotic episodes is not unduly high.
If the psychosis was related to other drugs, or arose de novo out of the blue, then I would suggest that you dont provide him/her with a chemical which could potentially disturb them in a big way.For their best interests and for the sake of your peace of mind.
Are they still on treatment for the psychosis, or do they have a family history of psychiatric disorders?
I am paranoid of my brain. It thinks all the time, even when I'm asleep. My thoughts assail me. Murderous lechers they are. Thought is the assassin of thought. Like a man stabbing himself with one hand while the other hand tries to stop the blade. Like an explosion that destroys the detonator. I am paranoid of my brain. It makes me unsettled and ill at ease. Makes me chase my tail, freezes my eyes and shuts me down. Watches me. Eats my head. It destroys me.