Most write-ups of SS-31 stop at mitochondria — cardiolipin binding, cristae structure, ATP. Almost none mention that the largest active trial of this peptide anywhere in the world is an eye trial. If you want to know what SS-31 research actually looks like in 2026, the honest answer is: a daily subcutaneous injection being tested in people losing central vision to dry age-related macular degeneration, on the back of a phase 2 that missed both of its primary endpoints.

That's not a gotcha. It's the most interesting regulatory story attached to this compound, and it explains something that trips up a lot of Australian readers asking "what is SS-31" and "is SS-31 legal in Australia": the peptide has one approved use here-and-now (in the US, for an ultra-rare genetic disease), and one much bigger bet still unresolved.

What is SS-31 (elamipretide), briefly

SS-31 is a four-amino-acid, cell-permeable peptide (D-Arg-dimethylTyr-Lys-Phe) that accumulates in the inner mitochondrial membrane. It was originally pitched as a mitochondria-targeted antioxidant, but the mechanistic literature has since moved on: current reviews describe its primary action as binding cardiolipin, the signature phospholipid of the inner membrane, and altering the lipid environment that electron-transport-chain complexes assemble in — rather than scavenging free radicals directly (Int J Mol Sci 2025 review; Pharmacol Res 2025). More on the compound basics on our SS-31 profile page.

Why the eye? The retinal pigment epithelium and photoreceptors are among the most metabolically demanding tissues in the body, and mitochondrial dysfunction in the RPE is a leading hypothesis for early AMD. That's the rationale — a hypothesis, not a demonstrated mechanism in human retina.

The phase 2 that missed: ReCLAIM-2

ReCLAIM-2 (NCT03891875) was a randomised, double-masked, placebo-controlled phase 2 in dry AMD with non-central geographic atrophy. Participants took 40 mg elamipretide by daily subcutaneous injection — note that: injected under the skin, not into the eye — for 48 weeks.

It had two co-primary endpoints: change in low-luminance best-corrected visual acuity, and change in square-root-transformed geographic atrophy area on OCT. It hit neither. The published report is explicit that statistical significance was not reached on either primary measure (Ophthalmology Science, 2024).

What did move were secondary imaging measures built around the ellipsoid zone — the OCT band that corresponds to photoreceptor inner-segment mitochondria. Treated eyes showed roughly a 43% reduction in progression of total EZ attenuation and about 47% for partial EZ attenuation versus placebo at week 48. A responder analysis also found more treated participants gained ≥10 letters of low-luminance BCVA (14.6% vs 2.1%).

Read that honestly: those are secondary findings in a trial that failed its primaries, in a single study, and they have not been replicated in a confirmatory trial. A 43% slowing of an imaging measure is not a 43% preservation of anyone's sight.

When the secondary endpoint becomes the primary

Here's the part worth understanding, because it's how modern ophthalmology drug development actually works. Rather than abandon the programme, the sponsor moved the EZ measure to the front.

The phase 3 ReNEW trial (NCT06373731) randomises roughly 360 participants 2:1 to daily subcutaneous elamipretide or placebo, with a 96-week treatment period, and its primary endpoint is the rate of change in the macular area of photoreceptor loss measured by SD-OCT ellipsoid zone mapping. A companion trial, ReGAIN, was announced alongside it. The sponsor reported reaching 50% of ReNEW's enrolment target in March 2025 (press release), and in its April 2026 commercial and pipeline update said ReNEW is fully enrolled, tracking to completion in late 2027, and that FDA guidance supports the potential for a single trial to serve as the basis for approval (Stealth BioTherapeutics). That last point is a company characterisation of regulator feedback, not a published FDA document — treat it as such.

EZ loss is genuinely gaining traction as an endpoint in retinal trials, with review-level discussion of its correlation to visual acuity and microperimetry. But "emerging imaging endpoint" and "validated predictor of what patients notice" are different standards, and elamipretide is now the highest-profile test of the gap between them.

Is SS-31 legal in Australia? The regulatory position

Nothing about the eye programme changes the Australian picture, so be precise about it:

  • No ARTG registration. Elamipretide is not an approved medicine in Australia in any indication. It has no TGA registration, no PBS listing, and no approved Australian Product Information.
  • The only approval anywhere is narrow. The FDA granted accelerated approval on 19 September 2025 for Forzinity (elamipretide) to improve muscle strength in Barth syndrome patients weighing at least 30 kg — after an earlier complete response letter. Accelerated approval means confirmatory evidence is still owed.
  • The mitochondrial myopathy phase 3 failed. Elamipretide's phase 3 in primary mitochondrial myopathy missed both of its endpoints. That's the most directly relevant precedent for anyone extrapolating from "mitochondrial peptide" to "muscle and energy benefits."
  • Access pathways are clinician-gated. An unapproved therapeutic good can only reach an Australian patient through pathways such as the Special Access Scheme, Authorised Prescriber or a registered clinical trial — all doctor-initiated, none something a consumer arranges themselves.

There is a real local contrast, though. Australia was the first country outside the US to approve a geographic atrophy therapy: the TGA registered Syfovre (pegcetacoplan) in January 2025, an intravitreal complement inhibitor, for a population estimated at over 75,000 Australians (Retina Australia). So GA is a live Australian therapeutic area with an approved option — and elamipretide, if ReNEW succeeds, would be a very different proposition: a daily injection you give yourself, aimed at earlier photoreceptor loss rather than established lesion growth. That comparison is worth watching, not assuming.

What this means if you follow SS-31

Three practical points. First, the human evidence base for SS-31 is concentrated in rare mitochondrial disease and retinal disease — not in the general performance, fatigue or anti-ageing claims that dominate online write-ups. Second, every dose in the eye programme is 40 mg once daily subcutaneously under trial supervision with 48- and 96-week follow-up; the sports-nutrition framing of "a mitochondrial peptide" bears no resemblance to that. Third, the single biggest readout for this compound lands in late 2027, and it will be judged on an imaging endpoint whose clinical meaning is itself still being argued.

More compound-by-compound breakdowns in our peptides library, and you can join the free updates list if you want the ReNEW readout summarised plainly when it arrives.

FAQ

What is SS-31 (elamipretide) used for?

Its only approval anywhere is the FDA's September 2025 accelerated approval as Forzinity, to improve muscle strength in Barth syndrome patients weighing at least 30 kg. Everything else — dry AMD, mitochondrial myopathy, ageing — remains investigational, and the phase 3 in primary mitochondrial myopathy missed both endpoints.

Does SS-31 work for macular degeneration?

Unproven. The phase 2 ReCLAIM-2 trial missed both primary endpoints (low-luminance visual acuity and geographic atrophy area), though secondary imaging measures of photoreceptor-layer loss favoured treatment. The phase 3 ReNEW trial is fully enrolled with completion expected in late 2027.

Is SS-31 legal in Australia?

Elamipretide is not registered on the ARTG and is not an approved medicine in Australia. Supply of an unapproved therapeutic good can only occur through clinician-initiated pathways such as the Special Access Scheme, Authorised Prescriber, or a clinical trial.

What is the ellipsoid zone endpoint in SS-31 research?

The ellipsoid zone is an OCT band reflecting photoreceptor inner-segment mitochondria. Its rate of loss is the primary endpoint in the phase 3 ReNEW trial — an emerging imaging endpoint whose relationship to patient-noticeable vision change is still being established.

Sources

Not medical advice. Elamipretide (SS-31) is not registered on the ARTG and is not an approved medicine in Australia; its only approval anywhere is the FDA's narrow accelerated approval for Barth syndrome. retatrutide.net.au is independent, is not affiliated with any manufacturer or supplier, and does not sell or source compounds.