I was told by someone who should know (as they must manage post-operative pain) that opioids lower a person's pain threshold, period. I had never heard that before, and I was doubtful that the statement was correct.
As someone who studied the effects of opioids to become buprenorphine certified (when it was new), was the medical director of a drug and alcohol rehab facility (not a big deal) and ran a free inner city drug/alcohol/mental illness clinic (a big deal for me) as well as an ED doc (one major role of which is to manage pain), I thought I understood opioids pretty well, so was alarmed at this person's insistence that it was a known fact. I questioned whether perhaps they were referring to tachyphylaxis, the development of tolerance, the phenomenon of people on methadone maintenance having a decreased pain threshold, the occasional case of paradoxical decrease in pain threshold following perioperative fentanyl administration or opioid induced hyperalgesia (OIH), and several other circumstances in which opioids don't relieve pain as expected, to which they answered no.
It was pretty concerning to me that I wasn't aware of this. Granted, I haven't been keeping up on the literature about opioids specifically or pain in general. So I started searching the literature.
OIH has been described in the literature since the 1870-80s, and the most common conclusions seem to be that its mechanism is unknown, the incidence is unknown, it can be difficult to differentiate from tolerance, it occurs more often in certain populations (chronic users/addicts/people on methadone), etc.
The literature is (what a surprise) all over the place concerning the response of pain to opioids, but no where did I find a general opinion regarding opioids reducing a person's pain threshold in general, or even an opinion leaning towards that.
I'm hoping someone on this site with more knowledge on the subject can give me a more reliable response than the one I recently received. Do opioids in fact decrease a recipients' pain threshold without regard to special circumstances?
Edited to add: I should note that a number of review articles noted that healthy (non-using) volunteers given a single dose of an opioid had an ~2x increase in area of forearm skin sensitivity to a cold pressor test compared to controls, but that other modalities of pain production were mostly unaffected.
Edited to add: I forgot to include this very comprehensive review: A Comprehensive Review of Opioid-Induced Hyperalgesia