Hermans, Linda, Nijs, Jo, Calders, Patrick et al. · Pain practice : the official journal of World Institute of Pain · 2018 · DOI
This study tested whether morphine and naloxone (a drug that blocks opioid effects) change how pain is processed in people with ME/CFS, fibromyalgia, rheumatoid arthritis, and healthy controls. Researchers measured pain sensitivity and pain relief in response to these medications using pressure tests and ischemic pain. They found that morphine slightly reduced pain sensitivity in patient groups similarly to placebo, but neither morphine nor naloxone significantly changed how the body's natural pain-relief system worked.
Understanding why standard pain medications like morphine have limited effectiveness in ME/CFS and fibromyalgia is crucial for developing better treatments. This study provides mechanistic evidence that central sensitization in these conditions may not primarily involve opioid system dysfunction, redirecting research toward other pain-processing pathways. These findings may help explain why opioids are often ineffective or poorly tolerated in ME/CFS patients.
This study does not establish that opioids are never useful in ME/CFS or fibromyalgia—only that they do not work through the measured pain modulation mechanisms. The small sample sizes (10 and 11 patients per group) limit generalizability. A single acute dose of morphine may not reflect effects of chronic opioid therapy or long-term pain system changes.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Hermans, Linda, Nijs, Jo, Calders, Patrick, De Clerck, Luc, Moorkens, Greta, Hans, Guy, et al. (2018). Influence of Morphine and Naloxone on Pain Modulation in Rheumatoid Arthritis, Chronic Fatigue Syndrome/Fibromyalgia, and Controls: A Double-Blind, Randomized, Placebo-Controlled, Cross-Over Study.. Pain practice : the official journal of World Institute of Pain. https://doi.org/10.1111/papr.12613
BibTeX
@article{mecfsatlas-hermans-2018-influence-morphine,
author = {Hermans, Linda and Nijs, Jo and Calders, Patrick and De Clerck, Luc and Moorkens, Greta and Hans, Guy and Grosemans, Sofie and Roman De Mettelinge, Tine and Tuynman, Joanna and Meeus, Mira},
title = {Influence of Morphine and Naloxone on Pain Modulation in Rheumatoid Arthritis, Chronic Fatigue Syndrome/Fibromyalgia, and Controls: A Double-Blind, Randomized, Placebo-Controlled, Cross-Over Study.},
journal = {Pain practice : the official journal of World Institute of Pain},
year = {2018},
doi = {10.1111/papr.12613},
note = {PubMed: 28722815},
url = {https://www.mecfsatlas.com/evidence/hermans-2018-influence-morphine},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/hermans-2018-influence-morphine
Contribute
Private, reviewed by a human. Not a public comment thread.