In a post apocalyptic world, drugs would be a possibility when assessing survivors. I present the idea that on occasion, when searching the survivors bag, you encounter an empty or low medication bottle or baggie. This can clue you on that certain symptoms may be the result of drug use/misuse.
Red eyes? Conjunctivitis or pot usage..?
Slurred speech and cognitive issues? Signs of neurological damage via virus… or treatable with a days rest and some pickle juice..?
And if you think it to be too complex, just throw them in quarantine! A day’s rest should sober them up, and now you can properly assess the survivor like you would any other…. Just watch out for the aggressive remarks with the hungover survivor.