Doctor Explains: Does Low-Dose Naltrexone Help Fibromyalgia? What New Research Tells Us
Updated: Aug 30
Low-dose naltrexone (LDN) has attracted considerable interest among people living with fibromyalgia, ME/CFS and other chronic pain conditions. Some patients report improvements in pain, fatigue, sleep or brain fog, while others notice little or no benefit.
So what does the latest research actually tell us?
A new exploratory analysis of the FINAL randomised controlled trial, published in 2026, has looked specifically at whether individual symptoms of fibromyalgia respond to low-dose naltrexone. The findings are useful because they remind us how important it is to look beyond average results and understand that chronic illnesses can affect people differently.
As an ME/CFS specialist, I also think this research is relevant to people who have both fibromyalgia and ME/CFS, although it is important not to assume that a treatment shown—or not shown—to work in fibromyalgia will necessarily work for ME/CFS.
What is low-dose naltrexone?
Naltrexone is an established medicine that is normally used at standard doses in the treatment of opioid and alcohol dependence. Low-dose naltrexone uses substantially smaller doses, generally in the range of a few milligrams.
The reason LDN has attracted interest in fibromyalgia is that researchers have proposed several possible effects on pain-processing pathways and neuroimmune mechanisms. Earlier small studies suggested that LDN might reduce pain and some other fibromyalgia symptoms.
However, small early studies can sometimes produce encouraging results that are not confirmed when a larger, more rigorous trial is performed.
That is why the newer evidence is important.
Post-Exertional Malaise (PEM) and fibromyalgia: why the distinction matters
Fibromyalgia and ME/CFS can overlap, but they are not the same condition.
Fibromyalgia is primarily characterised by chronic widespread pain, altered pain processing and a range of associated symptoms. ME/CFS has a distinctive feature known as Post-Exertional Malaise (PEM)—a delayed worsening of symptoms following physical, cognitive or emotional exertion.
Post-Exertional Malaise (PEM) can involve a substantial increase in fatigue, cognitive problems, pain, sleep disturbance and other symptoms. It is particularly important when assessing someone who may have both conditions.
For this reason, an online ME/CFS doctor should not simply assume that a medication being considered for fibromyalgia is automatically appropriate for ME/CFS.
Post-Exertional Malaise (PEM) and the latest LDN research
The original FINAL trial involved 99 women with fibromyalgia, who were randomly assigned to receive either low-dose naltrexone or placebo for 12 weeks.
The main trial found that LDN did not significantly reduce pain more than placebo. The average reduction in pain was greater numerically with LDN, but the difference between the groups was not statistically significant.
This is an important result.
It does not mean that nobody responds to LDN. Rather, it means that the study did not demonstrate a clear overall pain-relieving effect across the whole group.
The 2026 exploratory analysis went a step further. Researchers looked at six additional fibromyalgia symptoms:
fatigue
sleep disturbance
memory problems
stiffness
tenderness
depression
They examined the proportion of patients achieving at least a 30% improvement in each symptom.
Interestingly, none of the differences between LDN and placebo reached statistical significance. Memory showed the largest apparent difference, but the confidence interval was wide and crossed the point of no difference.
This means that the study does not provide strong evidence that LDN improves fatigue, sleep, memory, stiffness, tenderness or depression in fibromyalgia.
Does this mean LDN does not work at all?
Not necessarily.
This is where interpreting medical research carefully becomes important.
Previous smaller trials have reported potential benefits from LDN in fibromyalgia. For example, an earlier randomised crossover study involving 31 women reported a greater reduction in pain with 4.5 mg LDN than placebo.
Other research has produced mixed findings. A separate randomised trial involving 58 patients did not find a clinically relevant analgesic benefit, while systematic reviews and meta-analyses have reached somewhat different conclusions depending on which trials and outcomes were included.
Therefore, the fairest interpretation is that LDN remains an area of interest, but the evidence is not sufficiently consistent to describe it as a proven treatment for fibromyalgia.
What about LDN for ME/CFS?
This is an especially important question for people searching for an ME/CFS therapy.
The fibromyalgia studies do not establish that LDN treats ME/CFS.
At present, there is no high-quality evidence from a large randomised controlled trial demonstrating that LDN improves the core features of ME/CFS, particularly Post-Exertional Malaise (PEM).
This distinction matters because ME/CFS management needs to address the characteristic pattern of activity intolerance and Post-Exertional Malaise (PEM), rather than treating fatigue as an isolated symptom.
People with ME/CFS may also have co-existing fibromyalgia. In that situation, a clinician may consider whether treatment aimed at pain could potentially be useful for an individual patient. However, that is a clinical decision based on the person's overall circumstances—not evidence that LDN is a specific treatment for ME/CFS.
What does this mean for patients?
If you have fibromyalgia, ME/CFS, Long COVID or post-viral fatigue, it can be tempting to search for a single medication that will improve everything.
Unfortunately, these conditions are more complicated than that.
An ME/CFS specialist will usually consider the whole symptom pattern, including Post-Exertional Malaise (PEM), sleep, pain, cognitive symptoms, autonomic symptoms and functional limitations. Appropriate ME/CFS testing may also be needed to exclude other causes of symptoms or identify co-existing conditions.
Similarly, someone looking for a fibromyalgia specialist online may benefit from an assessment that considers whether their symptoms fit fibromyalgia alone, ME/CFS, both conditions, or another diagnosis.
For people with persistent fatigue following an infection, a post viral fatigue doctor or specialist working in a Long COVID fatigue clinic can also help distinguish Long COVID from ME/CFS and other causes of persistent symptoms.
ME/CFS research is changing how we think about treatment
One positive aspect of the growing research into ME/CFS, Long COVID and fibromyalgia is that researchers are increasingly studying these conditions as complex biological disorders rather than simply viewing fatigue or pain in isolation.
ME/CFS research is examining immune function, metabolism, neurological mechanisms, vascular abnormalities and other biological pathways. Better ME/CFS testing and more targeted ME/CFS therapy will ultimately depend on understanding these mechanisms more clearly.
The LDN story is a good example of why rigorous research matters. Early findings can be encouraging, but larger and better-controlled studies are essential before a treatment can be considered established.
For now, LDN remains an interesting potential treatment for fibromyalgia, but the newest evidence does not demonstrate a significant improvement in the range of symptoms studied. It should not be presented as a proven treatment for fibromyalgia—and there is even less evidence for using it specifically to treat ME/CFS or Post-Exertional Malaise (PEM).
Find out more
If you would like a specialist assessment, you can book an online consultation with an ME/CFS specialist.
You can also learn more about Prof. Dmitry Pshezhetskiy and explore further information about ME/CFS, Long COVID, fibromyalgia, ME/CFS research, ME/CFS testing and ME/CFS therapy on the clinic blog.
Prof. Dmitry Pshezhetskiy, MBBS, PhD, MRCGP
GMC 7494518 — Registered Medical Practitioner (GP)
Medical Disclaimer: The information provided in this article is for general educational and informational purposes only and does not constitute personalized medical advice, formal diagnosis, or treatment planning. Reading this content or communicating via this website does not establish a doctor-patient relationship with Prof Dmitry Pshezhetskiy. ME/CFS affects every individual differently; strategies discussed may not be suitable or safe for your specific health situation. Always consult your GP, specialist healthcare team, or NHS 111 regarding your personal medical concerns. In a medical emergency, please dial 999 or visit your nearest Emergency Department immediately. For a full disclaimer, see Medical Disclaimer & Terms of Use in Terms and Conditions on the policies page.
Research referenced: Nielsen MJ, Vaegter HB, Bruun KD. Symptom Response to Low-Dose Naltrexone in Fibromyalgia: An Exploratory Analysis of the Randomized Placebo-Controlled FINAL Trial. Pain Management Nursing, 2026. PMID: 42586891.
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