MOTS-c, SS-31 and BPC-157 come up in chronic-fatigue discussions because of research on mitochondria, physical performance and tissue repair. The studies cover very different populations and outcomes. Understanding what each actually tested is essential before applying its findings to ME/CFS.
LDN also appears frequently in fatigue searches. It is not a peptide, although small studies in ME/CFS and long COVID make it relevant to the same conversation.
The first distinction is between persistent tiredness as a symptom and ME/CFS as a specific illness. The second is between measuring a biological pathway and showing that a treatment improves a patient’s life.
Chronic fatigue and ME/CFS are not interchangeable
ME/CFS involves substantial impairment and a characteristic combination of symptoms, including post-exertional malaise and unrefreshing sleep. Cognitive problems or orthostatic intolerance can also be part of the diagnostic picture. Diagnosis requires a clinical assessment and evaluation of other explanations. CDC diagnosis guidance.
Persistent fatigue can also accompany thyroid disease, anemia, sleep disorders and other conditions. NICE includes thyroid-function testing and blood tests such as a full blood count and ferritin in the assessment of suspected ME/CFS. The purpose is to investigate the person’s symptoms, rather than assume every exhausted patient has the same underlying problem. NICE NG206.
What the most discussed options have actually studied
| Compound | Relevant research | What it does not establish |
|---|---|---|
| MOTS-c | Mitochondrial gene-expression research in fatigue syndromes; exercise-related measurements in people; treatment experiments in mice | A demonstrated treatment benefit for people with ME/CFS |
| SS-31 / elamipretide | Randomized trials in primary mitochondrial myopathy; a specific FDA-approved product for Barth syndrome | Approval or proven efficacy for ME/CFS |
| BPC-157 | A brief safety pilot in two adults | Relief of chronic fatigue or prevention of post-exertional malaise |
| LDN | Three ME/CFS case reports and observational long-COVID studies | A reliable response rate from a randomized ME/CFS trial |
MOTS-c: an interesting signal, with a treatment question still open
A 2019 study investigated mitochondrial-derived peptide biology in people with chronic fatigue syndrome and Q fever fatigue syndrome. Researchers found differences in the expression of genes associated with MOTS-c and humanin. They did not find a corresponding between-group difference in measured MOTS-c production. This was not a trial in which patients were treated with MOTS-c. Raijmakers and colleagues.
A separate 2021 paper reported improved physical performance after MOTS-c treatment in mice. Its human experiment measured naturally occurring MOTS-c around exercise in 10 healthy young men; those participants were not receiving MOTS-c treatment. Reynolds and colleagues, Nature Communications.
Those are distinct findings: biological differences in fatigue syndromes, animal treatment results and an exercise-associated signal in healthy people. None demonstrates that giving MOTS-c to someone with ME/CFS improves fatigue or prevents a crash after activity.
SS-31: why the diagnosis and trial result matter
Elamipretide, also known as SS-31, targets mitochondrial biology. Its human research includes the MMPOWER-3 trial in 218 people with primary mitochondrial myopathy, a group of genetic mitochondrial disorders.
At 24 weeks, that randomized trial did not meet its main endpoints for walking distance or fatigue compared with placebo. That result belongs beside the earlier encouraging studies. MMPOWER-3.
There is also an important regulatory development: in September 2025, the FDA granted accelerated approval to Forzinity, an elamipretide product, for Barth syndrome in patients meeting its labeled criteria. That disease-specific approval does not establish an ME/CFS indication or make an independently sold “SS-31” product equivalent to the approved medicine. FDA approval announcement.
BPC-157: what a two-person pilot cannot answer
A 2025 human pilot described brief BPC-157 exposure in two adults and reported no measured adverse changes in the biomarkers tested. It did not investigate chronic-fatigue treatment. BPC-157 pilot.
The relevant questions for fatigue would include changes in symptoms and function, a suitable comparator, adverse effects over meaningful follow-up and effects on post-exertional symptoms. A short safety report cannot substitute for those outcomes.
LDN for fatigue: relevant, but not a peptide
A 2020 case series described three people with ME/CFS who reported varying improvements with LDN. Case reports can identify an idea worth testing, but cannot establish how often a treatment works. BMJ Case Reports.
In a retrospective study of 59 people with long COVID, LDN use was associated with improvements in fatigue and other symptoms. Without randomization and a placebo group, that association cannot isolate the medication’s effect. Bonilla and colleagues.
A published protocol for a randomized trial in post-COVID fatigue describes how researchers planned to test LDN. A protocol is a study plan, not a positive result. Trial protocol.
Rebody’s LDN care page describes consultation and capsule options. A prescription decision requires an individual assessment; these studies do not make LDN a proven treatment for every cause of fatigue.
How does post-exertional malaise change the conversation?
Post-exertional malaise is worsening after physical or mental activity that previously would have been tolerated. It is a central feature of ME/CFS. CDC guidance emphasizes avoiding symptom worsening when discussing activity. CDC clinical-care guidance.
That makes “more energy” an incomplete treatment claim. A meaningful study should assess what happens after activity, as well as how someone feels at a single appointment. Mouse endurance findings are not a reason to tell a person with ME/CFS to push through symptoms.
Where Category 2 peptides fit
FDA compounding status is compound- and policy-specific. Its current page distinguishes withdrawn nominations such as BPC-157 and MOTs-C from current Category 2 entries, including ipamorelin under 503B. None of these categories demonstrates a fatigue benefit. Check the current record rather than an undated peptide list. FDA safety page, checked October 17, 2026.
Do these studies show recovery from ME/CFS?
They do not. The MOTS-c fatigue study measured biological differences, rather than recovery after treatment. The SS-31 trial involved another diagnosis. LDN case reports and uncontrolled observations cannot establish a recovery rate. A report of one improved symptom should not be presented as evidence of disease reversal.
What should someone ask before considering treatment?
Ask whether the proposed treatment was studied in people with the same diagnosis, whether it improved symptoms or only a biomarker, and whether the study measured function and post-exertional worsening. Ask about adverse effects, interactions, product quality and the clinical plan for reassessment.
For a person whose fatigue has reduced work, family life or basic activity, those details are the substance of the decision. A mitochondrial mechanism is interesting; a measurable improvement in the right patient population is the outcome that matters.
Explore care with Rebody
Want to discuss LDN with a clinician?
Rebody offers low-dose naltrexone consultations and 30- or 90-capsule package options. LDN is not a peptide, and its availability does not establish a benefit for ME/CFS or unexplained fatigue.