Poison Resistance/Poison Immunity and being drunk

[Spore]

So my character is an Alchemist (Investigator class) who is in over his head into continental politics, magical artifacts and dark magic. So naturally I would figure an substance (ab)user to be a drunkard of some degree. He is intelligent and keen in using chemicals to augment his combat and to heal his wounds so I figured drinking and using drugs is something he would do to dull his mental pain as well. Now we're 3 levels away from poison immunity.

If I roleplay substance abuse (with poison resistance +6 and a base save of +5 no less) it would take him a lot to get drunk but he would be drunk eventually (and I could imagine him drinking what is effectively rubbing alcohol anyhow). Now that works until 11th level where suddenly (even if you would play that levelup over a few weeks of downtime) alcohol does NOT for you. He could invent meth and take it and be immune to its effects.

How would you handle this? Increasing resistance to drugs is common among drug abusers but a sudden immunity rips yourself out of the suspension of disbelief instantly. I don't want him to become an overly emotional character subsituting the numbing of his mental pain by physical pain (because even if I am fine with a drug using character, I am not fine with a sadomasochistic one) what would be the logical reaction? Should I abandon this part of my fluff altogether? He could always go full workaholic here (I can craft magical items, making me an alchemy based artificer).

[Geddy2112]

I would say that after so long, he has reached a point where alcohol(and any other drug for that matter) just can't provide the benefits(physically, mentally) in that your character seeks an escape, but it never comes. You might feel some effect, but they will not be enough to be mechanically detrimental. Also, he might be psychosomatically dependent-ala the classic experiment of giving people beer with no alcohol and watching them get "drunk" even though they are not drunk at all...

[Spore]

Psychosomatic drunkenness is a tad exotic for a simple roleplaying game but I think I can work with the "drinking because it doesn't do anything" part.

[Itsjustsoup.com]

Upgrade Yo' game Playa.

When the low hits don't do it no more you gotta go big.

Switch from poisons to Diseases.

Crazy? Yeah. Extreme. Yes? Plausible, Maybe?

What if there was a disease/brew you could cultivate that accessed dementia? or you could get off by fighting of the effects of disease?

[Spore]

I feel even a permanent cursed item would be a more logical decision by then.

[Hamste]

Or you can ask the GM if you could just lower your poison resistance. If the alcohol you drink happens to be poisoned sucks to be you but at least you are drunk.

Also as an investigator you should have access to a formula called Polypurpose Panacea which can still intoxicate you or give you hallucinations as well as a few other possibilities.

[Spore]

Also as an investigator you should have access to a formula called Polypurpose Panacea which can still intoxicate you or give you hallucinations as well as a few other possibilities.

"What do you mean, you're out of 1st level extracts? We didn't fight all day!
"Well, I WAS drunk for the last 4 hours. That counts, right?"

[Willie the Duck]

Have you read William Gibson's Neuromancer? He could spend lots of effort on finding away around it. Perhaps looking for a new 'poison' (mind effecting magic, maybe?), or looking for a way to defeat the immunity.