Thanks Vector. Yeah I wouldn't dare try a placebo, I'm sure it may convince him for a while that he's cured, but I'm pretty sure he has a real problem and it would come back regardless of whether he thought it was gone. The official name of it is schizophrenia paranoia, he takes medication to help him function (his condition was bad enough that if medication were not possible, we probably would have institutionalized him :/). He hears voices, feels things touching him that aren't there, has trouble with math beyond simple addition/subtraction/division/multiplication, is probably very forgetful (we often discuss the same things a few times a week, he acknowledges that we do that but insists the repetition helps), has trouble doing things on time and keeping a regular schedule, although he's teaching a class and working in a cafe now, so he's learning how to get around that.
He used to believe demons are reprogrammed his family to ignore him (he'd get weird enough that we had no idea how to talk to him), would break things, flip out for no apparent reason, or was easily provoked to anger. Now he's given up the demon thing (although he always asks me about it "just to make sure"), is relatively calm now but instead, he often starts crying out of nowhere, especially after he yawns. I never ask why he cries, but the few times my mom did, he said "it's getting dark outside" and at a different time, "I miss grandpa" (that grandpa has been gone for... 15 years now?)