My suggestion has nothing to do with magic-resist races. It's specifically around abusing self-poisoning. As I've thought a little more about it, I had this idea:
Consuming a poison does two new things: Starts a 24-hour toxicity timer (which is reset each time new poison is consumed), increases a toxicity variable
So random character A, let's just call her Cinera, drinks an herbal brew. His affects now show Poison 2hrs and Toxicity 24hrs. 3 ticks later he shows only Toxicity 21hrs (since poison has expired). The toxicity variable is equal to the initial value of timer = 24. Every tick, toxicity variable goes down. So after 3 ticks (in above scenario) both the timer and variable = 21. Now, if Cinera consumes another poison at this moment, the timer resets to 24, but the variable gets +24 ( for total = 45 ).
Everyone with me so far?
As this trend continues, basically a threshold needs to be established above which, Cinera goes toxic. So let's say that threshold is 60. If Cinera consumes another poison (+24 toxicity) within the next 8 hours, their toxicity > 60 and thus become toxic (or has an increasingly high chance to). Otherwise, once the timer hits 0, so does the toxicity variable regardless of how high it was. So in other words, if you're using poison every once in a while - you're fine. But if you're puttin' 'em back like a dwarf at a desert bar...it comes with a risk.
The penalty for becoming toxic can be up for discussion but this is what my OP was about. Now the key word here is "consumed" - cast/communed poison should not count toward this IMO.
