Elamipretide Side Effects: What Studies Report

What the literature reports at a glance

Elamipretide, written in some papers as SS-31 or MTP-131, is a four-amino-acid peptide that a 2025 review described as concentrating in mitochondria and interacting with cardiolipin on the inner mitochondrial membrane (Elamipretide: A Review of Its Structure, Mechanism of Action, and Therapeutic Potential, IJMS 2025). The human tolerability record summarised below comes almost entirely from two rare-disease clinical programs in which the peptide was administered as a daily subcutaneous injection: a 24-week randomized trial in primary mitochondrial myopathy that did not meet its primary endpoints (MMPOWER-3, Neurology 2023) and a 168-week open-label extension in Barth syndrome that reported long-term tolerability in a small cohort (TAZPOWER open-label extension, Genetics in Medicine 2024). Across both of those reports, injection-site reactions were the adverse events described most consistently (PMID 37268435, PMID 38602181).

This page catalogues what published studies say about adverse events, tolerability and the boundaries of the evidence. It does not interpret those findings for any individual situation, and it makes no recommendation about use. The pharmacology, trial design and mitochondrial biology behind the molecule are covered separately in PeptideU's elamipretide course; this page stays on the safety-reporting question.

Where the human safety data come from

Two named trial programs supply the bulk of the published clinical experience. In primary mitochondrial myopathy, the randomized, double-blind, placebo-controlled MMPOWER-3 trial assigned adults to subcutaneous elamipretide 40 mg daily or placebo for 24 weeks and reported that the study did not meet its primary endpoints of change in six-minute walk test distance and total fatigue score (PMID 37268435). In Barth syndrome, an open-label extension of the TAZPOWER study followed a small group of participants receiving daily subcutaneous elamipretide 40 mg and reported efficacy and safety observations through 168 weeks (PMID 38602181).

A separate review in heart failure discussed elamipretide as a strategy for targeting mitochondrial dysfunction and summarised the clinical development work in cardiac and mitochondrial disease settings (Targeting mitochondrial dysfunction with elamipretide, Heart Failure Reviews 2022). Reviews of that kind aggregate earlier trial results rather than generating new adverse-event data, which matters when readers try to distinguish an independent safety observation from the same observation cited repeatedly.

Injection-Site Reactions: What Studies Report

The most repeatedly documented tolerability issue tracks with the route of administration rather than with any systemic organ effect. Because both clinical programs delivered the peptide by daily subcutaneous injection, local reactions dominated the reported adverse-event profile: researchers reported injection-site reactions in the 24-week randomized primary mitochondrial myopathy trial (PMID 37268435), and the 168-week Barth syndrome extension likewise reported injection-site reactions during prolonged daily dosing (PMID 38602181).

Published abstracts describe these reactions in categorical terms rather than by severity grade distribution, so the summaries available here do not support statements about how often a reaction led participants to stop treatment or about which local finding predominated. Where an abstract does not itemise that detail, the honest description is that the detail is not in the accessible summary, not that the reaction was mild.

Systemic and Other Adverse Events: What Studies Report

Beyond local injection-site findings, the verified sources summarised on this page do not itemise organ-specific toxicities, laboratory abnormalities or dose-limiting systemic events for elamipretide. The randomized trial in primary mitochondrial myopathy framed its headline result around unmet primary endpoints rather than around a new safety signal (PMID 37268435), and the Barth syndrome extension framed its headline result around long-term efficacy and safety in a small cohort followed for 168 weeks (PMID 38602181).

That is a description of what the literature covers, not a claim that nothing else occurs. Stated plainly: a detailed public tabulation of systemic adverse events by frequency and severity is not present in the sources cited here, and any page that presents such a table without a source has invented it.

Long-Term Exposure: What Studies Report

Duration is the axis on which most peptide safety literature is thinnest, which makes the Barth syndrome extension notable. Researchers followed participants for 168 weeks of open-label daily subcutaneous elamipretide and reported both efficacy measures and safety outcomes over that window (PMID 38602181). Two structural caveats belong alongside that finding. First, the cohort was small, as is typical for an ultra-rare disease program. Second, an open-label extension has no concurrent placebo group, so an event observed during the extension cannot be separated from the natural history of the underlying disease using the extension data alone.

Disease natural history in Barth syndrome includes cardiac involvement, illustrated by a case report describing cardiac pathology in a patient with a novel pathogenic TAFAZZIN variant (Cardiovascular Pathology, 2025), and by quality-of-life research documenting the burden patients and families described (Quality of life in Barth syndrome, Therapeutic Advances in Rare Disease, 2022). Those reports explain why attributing a clinical event to a drug rather than to the disease is difficult in this population.

Efficacy results are not safety results

A frequent misreading is to treat a failed efficacy trial as a safety verdict, in either direction. The 24-week randomized trial reported that elamipretide did not meet its primary endpoints in primary mitochondrial myopathy (PMID 37268435); that result speaks to measured functional outcomes, not to whether the compound was harmful. Conversely, the long-term extension's tolerability reporting in Barth syndrome does not transfer to other populations or indications (PMID 38602181).

Outcome measurement itself is contested in this field. A review of advances in primary mitochondrial myopathies discussed the heterogeneity of these disorders and the difficulty of selecting endpoints and trial designs capable of detecting change (Current Opinion in Neurology, 2019). When endpoints are insensitive, both benefit and harm become harder to quantify.

Animal and cell studies: what they can and cannot say about side effects

A substantial portion of the elamipretide literature is preclinical, and preclinical work characterises mechanism rather than human adverse events. Researchers reported neuroprotective effects of the mitochondrially targeted tetrapeptide in models of neurodegeneration (Frontiers in Integrative Neuroscience, 2021). A 2026 laboratory study reported that the mitochondrial-targeted SS-31 peptide attenuated radiation-induced cardiomyocyte senescence (Journal of Radiation Research, 2026). Another study used patient-derived induced pluripotent stem cell cardiomyocytes to examine mitochondria- and inflammasome-mediated mechanisms in clozapine-induced myocarditis (Molecular Psychiatry, 2025).

None of those designs generates human tolerability data. Cells and animals cannot report headache, fatigue or injection-site discomfort, doses are not interchangeable across species, and a favourable mechanistic result carries no information about what happens in a person over months of exposure. Reviews that summarise the mechanistic case describe cardiolipin interaction and mitochondrial membrane effects as the rationale for clinical testing rather than as evidence of clinical safety (PMID 39940712, PMID 35037146).

Populations with no published safety data

The clinical literature summarised here studied people with defined mitochondrial disorders, not healthy volunteers, athletes, or people seeking performance or anti-ageing outcomes. No trial in those groups appears among the verified sources, and that absence is a finding in itself. A 2026 review of approved and unapproved peptide therapies used for musculoskeletal injuries and athletic performance reported that safety and efficacy evidence for peptides used outside approved indications was limited (Sports Medicine, 2026).

Practical consequences of that gap, as the literature presents it:

• Adverse-event rates observed in a rare-disease cohort cannot be extrapolated to people without that disease (PMID 38602181).
• The only durations with published human follow-up in these sources are 24 weeks in a randomized setting (PMID 37268435) and 168 weeks open-label (PMID 38602181).
• Interaction data with other medications, pregnancy and lactation data, and paediatric data outside the studied programs are not addressed in the sources cited on this page.

How researchers describe unresolved questions

Reading the body of work together, several questions remain open in the published record. Whether elamipretide produces measurable functional benefit in primary mitochondrial myopathy was not resolved in favour of the peptide by the randomized 24-week trial (PMID 37268435). Whether long-term tolerability observed in a small Barth syndrome cohort generalises to larger or different populations was not established by the 168-week extension design (PMID 38602181). Whether the mechanistic effects reported in cell and animal models translate into clinically meaningful change remained a stated research question in the mechanistic review (PMID 39940712) and in the heart failure review discussing mitochondrial targeting (PMID 35037146).

Anyone evaluating a claim about elamipretide tolerability can ask four questions of the source: which population was studied, what route and duration were used, whether a comparator group existed, and whether the adverse event described appears in the cited paper at all.

Educational disclaimer

This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical question, symptom, medication or investigational therapy. It summarises what published studies reported and does not recommend, endorse or describe use of any compound.

References

• Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial (Neurology, 2023)
• Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER (Genetics in Medicine, 2024)
• Elamipretide: A Review of Its Structure, Mechanism of Action, and Therapeutic Potential (International Journal of Molecular Sciences, 2025)
• Targeting mitochondrial dysfunction with elamipretide (Heart Failure Reviews, 2022)
• Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance (Sports Medicine, 2026)
• Quality of life in Barth syndrome (Therapeutic Advances in Rare Disease, 2022)
• Cardiac pathology in a patient with a novel pathogenic variant c.703del (p.Ile235SerfsTer4) of the TAFAZZIN gene (Cardiovascular Pathology, 2025)
• Advances in primary mitochondrial myopathies (Current Opinion in Neurology, 2019)
• Neuroprotective Effects of a Small Mitochondrially-Targeted Tetrapeptide Elamipretide in Neurodegeneration (Frontiers in Integrative Neuroscience, 2021)
• Mitochondrial-targeted SS-31 peptide attenuates radiation-induced cardiomyocyte senescence (Journal of Radiation Research, 2026)
• Examination of mitochondria- and inflammasome-mediated mechanisms of clozapine-induced myocarditis using patient-derived iPSC cardiomyocytes (Molecular Psychiatry, 2025)