Fibromyalgia vs ME/CFS — Clinical Trial Comparison
Fibromyalgia
Widespread pain and central sensitisation
ME/CFS
Profound fatigue with post-exertional malaise
Fibromyalgia and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are frequently confused and often co-occur. Both involve central nervous system dysfunction, unrefreshing sleep, and cognitive difficulties. However, fibromyalgia is primarily a pain condition while ME/CFS is defined by debilitating fatigue worsened by exertion. Their trial landscapes are evolving rapidly, with Long COVID research driving new investment.
Key Differences at a Glance
| Feature | Fibromyalgia | ME/CFS |
|---|---|---|
| Primary symptom | Widespread musculoskeletal pain (widespread pain index ≥ 4) | Profound fatigue with post-exertional malaise (PEM) |
| UK prevalence | ~2–4% of adults (~1.2–2.5 million) | ~250,000 people (increasing post-COVID) |
| Hallmark feature | Widespread pain, tender points, hyperalgesia | Post-exertional malaise — symptoms worsen 12–72 hours after effort |
| Diagnostic criteria | 2016 ACR criteria (widespread pain index + symptom severity) | 2021 NICE guideline NG206 (essential: PEM, unrefreshing sleep, activity limitation) |
| Overlap with the other | ~30–50% also meet ME/CFS criteria | ~20–70% also meet fibromyalgia criteria |
| NICE treatment approach | Exercise, CBT, amitriptyline, duloxetine, pregabalin | Pacing, symptom management, CBT for coping (not cure), graded exercise NOT recommended |
Clinical Trial Availability
| Trial Aspect | Fibromyalgia | ME/CFS |
|---|---|---|
| UK trials actively recruiting | 15–25 studies | 10–20 studies (growing fast) |
| Most common trial phase | Phase 2–3 | Phase 1–2 (field is earlier-stage) |
| Top interventions tested | Low-dose naltrexone, cannabinoids, neuromodulation, novel analgesics, digital CBT | Antivirals, immunomodulators, mitochondrial support, autoantibody therapies, pacing apps |
| Drug trials | Moderate number (pain modulators, CNS agents) | Few (field historically neglected, now expanding) |
| Long COVID overlap | Some shared trials | Major overlap — many Long COVID trials include ME/CFS sub-studies |
| Non-drug trials | Many (exercise, acupuncture, CBT, TMS) | Moderate (pacing, diet, CBT for coping) |
Exciting Emerging Treatments
Fibromyalgia Trials
- Low-dose naltrexone (LDN) — modulating glial cell activation to reduce central sensitisation
- Medical cannabis and cannabinoids — UK trials testing CBD/THC formulations for pain
- Transcranial magnetic stimulation (TMS) — non-invasive brain stimulation for pain modulation
- Transcutaneous vagus nerve stimulation (tVNS) — targeting the vagus nerve for pain relief
- Nerve growth factor (NGF) inhibitors — novel pain pathway targeting
- Wearable-guided activity pacing — technology to optimise activity within pain thresholds
ME/CFS Trials
- BC007 (autoantibody removal) — German trial targeting functional autoantibodies in ME/CFS
- Low-dose naltrexone — shared with fibromyalgia, testing for fatigue and neuroinflammation
- Antiviral therapies — targeting persistent viral triggers (herpesviruses, enteroviruses)
- Mitochondrial support agents — coenzyme Q10, L-carnitine, oxaloacetate
- Immunoadsorption/plasmapheresis — removing autoantibodies in severe ME/CFS
- Digital health monitoring — wearable-based pacing guidance and activity tracking
💡 Long COVID has changed the research landscape
Long COVID shares many features with ME/CFS (fatigue, PEM, brain fog) and fibromyalgia (widespread pain). This has attracted significant new research funding to the UK. Many Long COVID trials now include ME/CFS and fibromyalgia sub-studies, and new drug trials targeting shared biology (neuroinflammation, autoimmunity, mitochondrial dysfunction) are expanding options for all three conditions.
Eligibility Differences
Fibromyalgia Trial Criteria
- Confirmed fibromyalgia diagnosis using ACR 2016 criteria
- Pain severity thresholds (typically visual analogue scale ≥ 4 or FIQR score requirements)
- Stable medication for specified period before enrolment (usually 4–8 weeks)
- Exclusion of other inflammatory rheumatic diseases (RA, lupus) that could explain symptoms
- Some trials exclude co-existing ME/CFS, others specifically target the overlap
ME/CFS Trial Criteria
- Diagnosis per NICE NG206 criteria (essential: PEM, activity limitation, unrefreshing sleep)
- Symptom duration typically ≥ 3–6 months
- Severity stratification (mild: mobile, moderate: reduced mobility, severe: housebound/bedbound)
- Exclusion of alternative diagnoses (thyroid disease, anaemia, depression as primary)
- Actigraphy or wearable monitoring increasingly used to objectively measure activity and PEM
⚡ Fibromyalgia Trials
Find actively recruiting fibromyalgia clinical trials across the UK
View Fibromyalgia Trials