And there are drug reps telling you this medication is not addictive and that you're being negligent in leaving pain "untreated".
So, you ask everyone if they're in pain. A load of them say "yes", and you can't afford to give them physical therapy and psychological support but you can give them opioids which are dirt cheap and you've been told they're not addictive if used to treat pain. You end up flooding communities with opioid meds. You have a bunch of people still in pain, and with an opioid addiction. And then you have their friends and relatives who aren't in pain but who want to try these meds recreationally getting hooked.
It's a public health disaster.
To answer your question: ask people about pain, but set expectations first. Opioids are a poor choice for most people with long term pain.
Not a doctor, but I would think that cortisol ("stress hormone") levels would correlate pretty well with what we think of as pain, since it does stress you out and would persist over long-term pain. And vice versa for dopamine.
