I heard about people with ADHD being more resistant to stimulants, which is also something I experience as an ADHD patient. Caffeine and nicotine only make me feel focused, not buzzed, which I heard is a common trait we have; I quit smoking and vaping, to clarify. I'm not saying you intend for Mezz to have ADHD, it just reminded me of that.
Funny enough, depressants are the exact opposite for me, making me feel absolutely terrified. The only depressant I could handle was alcohol, although I quit that, too. Don't quote me on the pharmacological aspects relating to any of this, I'm not an expert. I also have autism, which may or may not affect how I react to some drugs, I really have no clue.
This talk of stimulants made me think of something interesting, though I'll share it privately, for whenever you have the time to read it.