remove THC from the addict trait

[awfulworldkid]

It would be interesting if tolerance was a factor, and an addict that routinely exposes themselves to a chem would have to take increasingly larger amounts to both have an effect and satisfy their addiction.

The idea of someone addicted to sarin becoming so tolerant to it that it's like soda pop to them would be funny and lead to some Princess Bride gambits

That's brilliant actually. 
For the super toxic chems just start the addict out with a high enough tolerance to not be immediately killed by the toxin. 
For extra fun, have two thresholds for poisonous chems. A lower one which satisfies the craving, and one juuust above it which is where the poison actually surpasses your tolerance. So a nerd addict can do some math and safely spend the round sipping on phlogiston, but get distracted and oops, overdose now you're on fire.

You should be able to addict yourself to dangerous chems without already being addicted, simply by taking sub-1u amounts of it repetitively until you build up enough of a tolerance to take addiction-worthy amounts. Would be hilarious to see a hard drinker become immune to alcohol and destroy the entire bar in drinking contests.