i have had a very similar experience to your friend myself (i have a long history of depression and anxiety, possibly some underlying bipolar)
the first time i dropped LSD, it was 10 hours of pure bliss and joy, i was living in each second and it was truly glorious. the second time, i had a abt 150 mcg of acid, and 18 hours later i was going to be the next buddha or jesus of the youth of today, i knew i could liberate everyone around me from their sorrow. then, i was in the most intense paranoia of my life. I was certain that pastelcircus was flying on a jet from california to kill me within 6 hours, i called the cops, telling them i feared for my life, then i realised the cops were a part of the conspiracy to kill me, so i walked to the botanical gardens in my city and went to the centre of it, and tried to meditate, so that i would be less vulnerable to psychic attacks (i believed that everyone with a weak mind could be used by a corporation [almost illuminati-esque] to observe me). i then saw an old woman who i felt was like a dream character, who i needed to talk to, she was really nice and understanding and walked me to the closest hospital.
after some time spent at the hospital thinking i could communicate telepathically, and kind of felt i had become a channel, i woke up in a closed mental health ward with the 10 most insane people in my state (there was a psycho coming down off a long meth bender and i was concerned for my life)
. against my will ofc. the reason i was put in a hardcore psychiatric ward was because i attacked my dad, because i was convinced he was a part of the organisation trying to kill me, i wasnt trying to hurt him though, i just pretended to atk him, i wanted him to be further away from me, because i was being disturbed by his energy.
at the closed ward i still had some very out there ideas, even on huge doses of olanzapine and a benzodiazepine, such as thinking that a girl in the ward could inhabit birds and watch me from any birds in the small yard, i still thought i had been michael the archangel in a past life, and that i had met my soulmate (another patient in the closed ward) who had been joan of arc in a past life, and that we were going to start a new kind of love era like the beatles in the 60's.
i got moved from the closed ward to an open ward after 2-3 weeks, then i was in the open ward (more relaxed but still seriously backwards in terms of treating mental illness) for 3-4 weeks, at that point i was still slightly delusional and wanted to move into a girls flat who i had just met (the one who could astral project and was joan of arc in a past life), and she was previously into occult and i wasnt really attracted to her. But i was mostly lucid.
anyway the story goes on etc, the psychiatric hospital was a bit soul crushing but i met some beautiful souls and had some amazing moments there
if you can visit him at the hospital and talk to him / maybe bring some very simple games to play, but he might have a very short attention span, just be very patient and try not to be judgemental at all. if he is on a mood stabiliser like olanzapine, maybe ask him if he has the munchies (i had weed munchies x20 for about 4 weeks) and bring him some mcdonalds or some other dope fast food lol, he will appreciate
. i was still quite disconnected from the world and unsure if i had broken myself for 1-2 months after my trip, but time healed me.
i was diagnosed bipolar after about 30 minutes of talking to the psychiatrist near the end of my stay at the open-ward (second psychiatric hospital i went to), it was apparent to me she was on some ego-trip and wanted to prescribe me a lot of strong mind altering drugs with a much stronger list of side-effects. i kindly said no thanks, i dont want to see you for any more appointments, and im still taking no drugs (it has been approx 7 months since the trip).
what will be beneficial for his recovery is abstinence from all drugs (i suppose if it truly triggered full on schizophrenia or bipolar then it would be harmful to himself and others for him to refuse medication) , i also see a dr regularly who is vigilant in being concerned that i will have another manic episode and end up in a psychiatric ward again, what i do to prevent this happening is making sure i do not go multiple nights without sleep, and i try to keep my mind in balance by practicing self-awareness and if i notice i am becoming un-grounded, a long hike in the hills is good, or some yoga or relaxation exercises. If i cant sleep for the second or third night in a row, i will smoke some indica (my preference, not really sure if thats a gd recommendation for others), or i will take 25mg of seroquel an hour before bed and that will knock me out. u dont want to be sleep deprived if you are very sensitive to mood imbalances which can go out of control! regular exercise and regular meditation
how long is he at the mental hospital for? try to see him as much as possible (if he has some base in reality yet), he probably misses his friends and wants a hug, send him my love