I don’t have any mental illnesses of which I’m aware, but it depends on how bad the illness was if I did. Is it debilitating? Am I regularly having suicide ideation? Am I miserable all the time because of my depression? Is it running my marriage, my friendships? Yeah, I’d take it. 20% is pretty high odds, but if I’m so I’ll I’m considering suicide already, 70% of being cured sounds good. Wouldn’t you?
Is my illness such that I have sad days a couple of times a month? But 20% chance of getting a permanent psychosis? Probably not worth the risk.
If the perceived goodness value * % chance good outcome is greater than the perceived badness value * % chance of a bad outcome, then “Yes.” That’s the basis of Pascal’s Wager, and it’s a good a decision process as any I know.
Oh, heck… if I’m honest, I’d probably take MDMA recreationally at least once just to see what it’s like, if it were legal and available.