I thought this was interesting, and possibly useful. They measured pain in Fibromyalgia, but there seems to be crossover with topics discussed here. From 2012 Excerpts only. Study published in the AAPM 2012; Abstract 251.
Naltrexone May Lessen Chronic Pain - MedPage Today
Published: Feb 26, 2012
PALM SPRINGS, Calif. -- Low doses of the opioid antagonist naltrexone (ReVia) may relieve pain associated with fibromyalgia compared with placebo by targeting the immune pathway of pain.
In a small, randomized crossover trial, fibromyalgia patients reported significantly greater reductions in pain with naltrexone than with placebo.
"The key here is not in its opioid antagonistic effects, but in a separate action on microglia," Younger said.
Interest has been growing in the immune pathways involved in pain. At the heart of the research are the body's glial cells -- including microglia and astrocytes -- which disperse inflammatory cytokines when activated by certain biological triggers, such as opioids.
To hamper that inflammatory response, researchers have been targeting the toll-like-receptor-4 (TLR-4) on glial cells.
Indeed, Younger said naltrexone can stifle the immune response and, ultimately, symptoms of fibromyalgia by blocking TLR-4 on microglia.
Younger and colleagues found that patients reported an overall greater reduction in pain when they were on low-dose naltrexone than when they took placebo (48.5% versus 27.4%,P=0.006).
In addition to the half of patients who reported feeling very much or much improved when on low-dose naltrexone, an additional quarter felt minimally improved, Younger said.
Other drugs may have also improved pain via the immune pathway, including naloxone, fluorocitrate, minocycline, and dextromethorphan, Younger said. Generic versions of some of these drugs are available, which would make them significantly less expensive, he added.
"Immunologists have ignored pain, and pain people have ignored immunology," Watkins said. "That has to end. They are intertwined."