This stat is not one of the Stats on the main screen, its level can only be seen on the Character screen on the Characteristics tab.
It is measured in percent.
What affects my value Edit
It measures how your character is affected to toxins caused by what you consume. These include food and drink, and Drugs you take.
Some foods increase your Intoxication value and a few can reduce it.
Time will also reduce it so if you know you have taken some recently (in game time) or are going to take a lot due to injuries check your level to try to avoid dangerous levels.
Dangerous levels Edit
The only reason to be concerned on this is when the level reaches above 20% there is increased chance of getting the Disease Intoxication to which there is no cure but only lasts a few days.