Shrooms are a poison and are not very good for the liver either. But they are better than most drugs. Psilocybin mushrooms don't do much physical harm to the body, but it is a toxin, a fungus that has to be filtered through the liver. Which is why some get stomach aches after consuming them. Would be a better alternative than alcohol that's for sure but again I would let your body rest for a while.
Also shrooms are not for everyone lots of people can't stomach them and don't enjoy the high. Someone with liver damage from alcohol would probably get bad stomach aches from them.
I think cannabis is the best drug for him but the OP doesn't like it. I don't think he has many options besides cannabis and letting his body rest.
I supose acid isn't very hard on the body but its got its own set of problems such as being extremely hard on the brain.