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What it is
SS-31 is a synthetic four-amino-acid peptide designed to concentrate at the inner mitochondrial membrane. It later received the generic name elamipretide and has also been studied under the names MTP-131 and Bendavia.
In September 2025, the FDA granted accelerated approval to Forzinity, an elamipretide injection, to improve muscle strength in adults and children with Barth syndrome who weigh at least 30 kg. That approval applies to the regulated drug and that specific rare disease. It does not make research-market SS-31 vials approved products or validate general anti-aging use.
What people research it for
Improved muscle strength in Barth syndrome
Human studiesForzinity received accelerated FDA approval based on increases in knee-extensor strength during a small open-label extension. A confirmatory trial is required to verify patient benefit.
Possible longer-term functional gains in Barth syndrome
Early human dataEight participants followed through 168 weeks in the extension, with descriptive gains in muscle strength. The lack of a long-term placebo group makes the size of benefit uncertain.
No overall benefit in primary mitochondrial myopathy
Human studiesThe 218-person MMPOWER-3 trial found no improvement over placebo in six-minute walk distance or fatigue at 24 weeks. This important negative result limits broad claims.
Genotype-specific research signal
Early human dataPost hoc analyses suggested better walking outcomes in some nuclear-DNA mitochondrial maintenance disorders, especially a CPEO subgroup. These exploratory findings require prospective confirmation.
How it works
Elamipretide binds cardiolipin, a phospholipid concentrated in the inner mitochondrial membrane. Cardiolipin helps organize the folds called cristae and supports the protein complexes that generate cellular energy. Barth syndrome disrupts cardiolipin remodeling, which provides a direct biological reason to study this target in that disease.
Laboratory and clinical research suggests that the peptide can support mitochondrial structure and energy production under some forms of stress. The mechanism is more specific than acting as a general antioxidant, but a plausible mitochondrial mechanism does not mean it improves energy, exercise capacity, or aging in every population.
What the research actually shows
The pivotal Barth syndrome evidence came from SPIBA-201, a 12-person randomized crossover trial followed by an open-label extension. During the initial 12-week comparison, elamipretide was not superior to placebo on the six-minute walk test or fatigue score. Those negative randomized results matter because the later improvement was not observed under the same controlled conditions.
During the open-label extension, median knee-extensor strength increased from a baseline of 124 newtons, with a median change of 34 newtons at week 12 and 63 newtons among eight participants at week 168. The FDA treated muscle strength as an intermediate endpoint reasonably likely to predict benefit and required a post-approval randomized trial to confirm that it translates into better function.
The published SPIBA-201 report also described eight participants who reached 36 weeks. At that point, six-minute walk distance had increased by 95.9 meters and the Barth syndrome symptom score improved by 2.1 points. Because everyone knew they were receiving elamipretide during this extension, the result is supportive but less conclusive than a blinded placebo comparison.
The much larger MMPOWER-3 trial enrolled 218 adults with genetically confirmed primary mitochondrial myopathy. Participants received elamipretide or placebo for 24 weeks. The between-group difference in six-minute walk distance was -3.2 meters, with a 95 percent confidence interval from -18.7 to 12.3, and fatigue scores also did not differ. The study provided Class I evidence of no overall benefit on those endpoints.
A later post hoc analysis divided MMPOWER-3 participants by genetic cause. A subgroup with mitochondrial DNA maintenance disorders and chronic progressive external ophthalmoplegia showed a 37.3-meter mean improvement in walking distance versus an 8.0-meter decline with placebo. Because this was a subgroup analysis after the overall trial failed, it is a hypothesis for a new trial rather than proof of effectiveness.
The evidence therefore has two distinct messages. Elamipretide is an FDA-approved drug for a narrowly defined Barth syndrome population under accelerated approval, but broad claims about exercise, fatigue, wellness, or longevity are not established and include a major negative phase 3 trial.
Handling & storage
Storage at a glance
Published stability data- Lyophilized
- below -18°C for long-term storage
- about 3 weeks at room temperature according to the manufacturer technical sheet
- Store desiccated and separate from the approved liquid Forzinity product.
- Reconstituted
- 4°C
- Use within 2 to 7 days
- ProSpec technical-sheet guidance. A longer retail claim lacks a public compound-specific assay.
- Light
- Protect from light.
- Room temperature
- Dry lyophilized material is listed as stable for about 3 weeks at room temperature.
- Reconstitution
- manufacturer-specified sterile diluent
- For longer laboratory storage, use frozen single-use aliquots and avoid repeated freezing and thawing.
Basis: Published stability data. Sources: ProSpec elamipretide technical product page, Peptify SS-31 storage guidance, QSC SS-31 research-vial guidance
The approved Forzinity product is a regulated liquid drug with its own prescribing information and should not be confused with lyophilized research-market SS-31. The card below applies only to the checked research material, not to Forzinity or to patient care.
For lyophilized research SS-31, the manufacturer technical sheet calls for long-term storage below -18°C and says dry material is stable for about three weeks at room temperature. After reconstitution it gives a short 2 to 7 day window at 4°C. A retail source lists a longer 28-day refrigerated window, but that less conservative claim was not supported by a public compound-specific assay.
Safety & cautions
The FDA label and trial summary identify allergic reactions, including serious reactions requiring emergency care, and frequent injection-site reactions. In the 12-person controlled Barth syndrome trial, all elamipretide-treated participants had a local administration reaction, and redness, pain, itching, and induration were common.
Accelerated approval means the FDA accepted an intermediate endpoint considered reasonably likely to predict benefit. It does not mean every clinical outcome has been confirmed. The manufacturer must complete a randomized post-approval study.
Research-market SS-31 is not interchangeable with Forzinity. Unregulated vials can differ in identity, purity, concentration, sterility, and endotoxin burden, and their storage claims are not the approved drug's specifications.
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Frequently asked questions
Is SS-31 FDA approved?
Elamipretide is FDA approved under the brand Forzinity to improve muscle strength in adults and children with Barth syndrome who weigh at least 30 kg. Research-market SS-31 vials are not approved drugs.
What is accelerated approval?
It allows approval based on an intermediate measure considered reasonably likely to predict clinical benefit. Forzinity's approval relied on muscle-strength findings, and a confirmatory randomized trial is required.
Did the Barth syndrome trial meet its original endpoints?
No. The initial randomized portion did not show superiority on walking distance or fatigue. Muscle-strength gains appeared during the longer open-label extension.
Does SS-31 improve fatigue in mitochondrial disease?
Not across the broad population studied in MMPOWER-3. That 218-person phase 3 trial found no benefit over placebo on fatigue or six-minute walk distance at 24 weeks.
Is SS-31 proven for longevity?
No. Mitochondrial targeting provides a research rationale, but controlled trials have not shown that elamipretide slows normal aging or extends human lifespan.
What side effects are documented?
The approved drug can cause allergic reactions and injection-site reactions. Redness, pain, itching, and induration were common in the small Barth syndrome trial.
How should lyophilized research SS-31 be stored?
The checked technical sheet lists long-term dry storage below -18°C and 2 to 7 days at 4°C after reconstitution. This research-material guidance does not replace Forzinity's prescribing information.
Sources
- FDA accelerated approval announcement for Forzinity
- FDA Drug Trials Snapshot for Forzinity
- FDA Forzinity prescribing information
- Thompson et al., SPIBA-201 Barth syndrome trial
- Karaa et al., MMPOWER-3 randomized clinical trial
- MMPOWER-3 genotype-specific post hoc analysis
- ProSpec elamipretide technical product page
- Peptify SS-31 storage guidance
- QSC SS-31 research-vial guidance
Last reviewed September 17, 2026. This guide is educational and research-focused, not medical advice. SS-31 products referenced on PeptidePub are sold by third parties as materials for laboratory research use only, not for human or animal consumption.
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