Research brief · 2026-09-09
What Does SS-31 Actually Do? What the Research Shows
SS-31, known clinically as elamipretide, is a synthetic peptide only four amino acids long. It was designed to concentrate inside the inner mitochondrial membrane and bind cardiolipin, a lipid mitochondria need to produce energy efficiently. It has never been approved as a medicine anywhere, despite more than a decade of development by Stealth BioTherapeutics.
Unlike most peptides sold online, SS-31 has a genuinely extensive and well-documented trial record: 21 registered trials, most completed with posted results or full publications. That is exactly what makes its repeated misses notable. In Barth syndrome, a rare genetic disease of heart and skeletal muscle, the randomized, blinded phase of the TAZPOWER trial did not meet either co-primary endpoint, a walking test and a fatigue score, in 12 participants, as Thompson and colleagues reported in Genetics in Medicine in 2020. The open-label extension published in 2024 did show sustained walking improvement to 168 weeks, but with no placebo comparison, that is weaker evidence.
In primary mitochondrial myopathy, the Phase 3 MMPOWER-3 trial, the largest test of this use, did not demonstrate a significant overall benefit according to its own investigators. A post hoc subgroup with nuclear-DNA-related disease showed a trend toward better walking distance, now being tested in a dedicated follow-up trial, per Karaa and colleagues in 2024.
In heart failure, Butler and colleagues in 2020 found no improvement in heart chamber volumes on MRI at either dose versus placebo. In dry age-related macular degeneration, the ReCLAIM-2 trial in 176 patients missed its vision and lesion-growth endpoints but significantly slowed a structural marker of photoreceptor loss, which is now the primary endpoint of an ongoing Phase 3.
The limit is the pattern itself: open-label extensions and small subgroups keep showing improvement that the core blinded comparisons do not. Whether that reflects real biology or the known optimism of unblinded data is unresolved. SS-31 is not approved for human use.
Sources
- Thompson WR et al., TAZPOWER: randomized trial of elamipretide in Barth syndrome, neither primary endpoint met in core phase
- Genetics in Medicine 2020
- Karaa A et al., Genotype-specific effects of elamipretide in primary mitochondrial myopathy, post hoc analysis of MMPOWER-3
- Orphanet Journal of Rare Diseases 2024
- Butler J et al., PROGRESS-HF Phase 2 trial of elamipretide in heart failure with reduced ejection fraction, n=71
- Journal of Cardiac Failure 2020
- Ehlers JP et al., ReCLAIM-2 randomized Phase 2 trial of elamipretide in dry age-related macular degeneration, n=176
- Ophthalmology Science 2024
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