SS-31 (Elamipretide): From Research to FDA Approval

Cellular Energy & Mitochondrial Research

SS-31 — known in the clinic as elamipretide — is a mitochondria-targeted peptide that has reached large randomized trials. Its record is mixed, and reading it honestly means noting both the wins and the misses.

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Findings

• In late 2025, elamipretide received its first FDA approval — SS-31’s clinical form is now an approved medicine.
• SS-31 (called elamipretide in the clinic) targets the mitochondria, the cell’s power plants, and has been tested in large randomized trials.
• In Barth syndrome, patients on long-term elamipretide walked about 96 metres farther in the standard six-minute walking test.
• In a trial for dry age-related macular degeneration, it reduced a key measure of retinal-cell loss by 43%.
• The Barth syndrome approval is the first ever for a mitochondria-targeted therapeutic of this class.

From trial compound to approved medicine (2025)

In late 2025, elamipretide received its first FDA approval, for Barth syndrome — making it the first cardiolipin-targeted mitochondrial therapeutic ever approved (“Elamipretide: First Approval,” Drugs, 2026). For a compound that began as a research peptide, that is the full distance: laboratory, randomized trials, approval.

The approval rests on the trial record covered below, with the Barth syndrome walking-distance gains carrying the weight. It also changes how the rest of the program reads: elamipretide is no longer a candidate molecule. It is a medicine with an expanding evidence base.

Barth syndrome: the clearest positive (Genet Med, 2024)

The TAZPOWER trial’s 168-week open-label extension followed patients with Barth syndrome on daily elamipretide 40 mg. Eight of ten patients reached the week-168 visit. There were significant improvements on the six-minute walk test at every time point, totalling a cumulative 96.1 metres of improvement (P=0.003 at week 168), along with improved fatigue scores and measurable gains in left-ventricular function. It was well tolerated, with injection-site reactions the most common adverse event.

Macular degeneration: positive on secondary measures (Ophthalmol Sci, 2024)

The Phase II ReCLAIM-2 trial in dry age-related macular degeneration did not meet its primary endpoints, but elamipretide produced a 43% reduction in progression of ellipsoid-zone loss (a marker of photoreceptor damage, P=0.0034) and significantly more patients gained at least 10 letters of low-luminance visual acuity (14.6% vs 2.1%, P=0.04).

Where it fell short (Neurology, 2023)

The pivotal Phase 3 MMPOWER-3 trial in primary mitochondrial myopathy (218 patients) did not meet its primary endpoints on the six-minute walk test or fatigue score, though treatment was well tolerated. The compound’s human story is therefore condition-specific rather than uniform.

What SS-31 is

SS-31 (elamipretide) is a mitochondria-targeted tetrapeptide that accumulates in the inner mitochondrial membrane, binding cardiolipin and studied for its effect on cellular energy. Our SS-31 buying guide covers the compound and its handling.

Frequently asked questions

Has SS-31 shown positive results in humans?

Yes, in specific settings. In a 168-week open-label extension in Barth syndrome patients, elamipretide (SS-31) produced a cumulative 96.1-metre improvement on the six-minute walk test and improvements in cardiac function. A macular-degeneration trial slowed a marker of photoreceptor loss.

Did every SS-31 trial succeed?

No, and it’s worth being precise. The large MMPOWER-3 primary mitochondrial myopathy trial did not meet its primary endpoints. The positive signals came in the Barth syndrome extension and, on secondary measures, in the eye-disease trial.

What is SS-31?

SS-31 (elamipretide) is a mitochondria-targeted tetrapeptide that concentrates in the inner mitochondrial membrane, where it is studied for its effect on cellular energy production.

Sources: Thompson WR, et al. Long-term efficacy and safety of elamipretide in Barth syndrome (TAZPOWER 168-week OLE). Genet Med. 2024;26:101138. PMID 38602181. Ehlers JP, et al. ReCLAIM-2: Elamipretide in age-related macular degeneration. Ophthalmol Sci. 2024;5:100628. PMID 39605874. Karaa A, et al. Elamipretide in primary mitochondrial myopathy (MMPOWER-3). Neurology. 2023;101:e238-e252. PMID 37268435.