Longevity
SS-31 (Elamipretide)
aka Elamipretide · SS-31 · MTP-131 · Bendavia · Forzinity · elamipretide hydrochloride · ss31
Grade
A peptide that homes in on the power plants of your cells to help them work better. It is now a genuine, if narrowly approved, medicine for one rare disease, but unproven for the anti-ageing uses it is hyped for.
- Class
- Mitochondria-targeting (cardiolipin-binding) cell-penetrating tetrapeptide
- Evidence
- Grade B · Promising human evidence
- Sport / WADA
- Not specifically named on the WADA Prohibited List. As a metabolic/mitochondrial-function modifier it does not fall under the classic peptide-hormone or hormone-axis categories; athletes should nonetheless treat any unlicensed peptide with caution and seek anti-doping guidance, as status can change and S0 (non-approved substances) considerations may apply.
- Last reviewed
- 2026-06
Grade B · Promising human evidence
Why this grade
This is the rare peptide that genuinely earns more than a D. It has extensive human trial data and, in September 2025, received an FDA accelerated approval (as Forzinity, from Stealth BioTherapeutics) for the ultra-rare Barth syndrome, to improve muscle strength. That secures a real human-evidence floor in ONE narrow indication. The grade is B rather than A because: (1) it is an *accelerated* approval based on an intermediate surrogate endpoint (knee-extensor muscle strength), with confirmatory clinical-benefit trials still required and approval potentially revocable; (2) it covers a tiny rare-disease population, not the longevity/anti-ageing use it is sold for online; and (3) in the larger, common-disease indications it was actually developed for, it failed. The Phase 3 MMPOWER-3 trial in primary mitochondrial myopathy missed its co-primary endpoints, and programmes in heart failure (HFpEF) and dry AMD/geographic atrophy did not deliver. There is essentially NO human evidence for the healthy-ageing, anti-fatigue or general "mitochondrial rejuvenation" claims made by grey-market sellers; that part of the story is animal/in-vitro only. The grade applies to the molecule's evidence base overall, not to the unlicensed "research chemical" version, which has none of its own.
What is it?
Every cell has tiny batteries called mitochondria that make its energy. In some rare diseases these batteries are damaged and people get very weak and tired. SS-31 is a small lab-made protein that sticks to a specific fatty part of the battery and helps it hold its shape and run more cleanly. After many years of testing, a medical version (brand name Forzinity) was approved in the US in 2025 for one rare inherited disease called Barth syndrome, where it improved muscle strength. When it was tried in bigger, more common problems like a different muscle disease and heart failure, it did not really work. There is no good human proof it slows ageing or boosts energy in healthy people, even though that is how it is sold online.
Think of it as a specialist repair technician for the cell's power plants. Unlike most peptides on these sites, it graduated to being a licensed medicine, but only for fixing one rare type of factory. When the same technician was sent to fix the much more common breakdowns (heart failure, ordinary muscle disease), it kept failing the job. The 'helps everyone age better' sales pitch is like hiring that one rare-disease specialist to service every machine in your house on the strength of a single niche success.
How is it meant to work?
A synthetic tetrapeptide that penetrates cells and accumulates in the inner mitochondrial membrane, where it binds the phospholipid cardiolipin. Cardiolipin organises the respiratory-chain complexes and the folded cristae structure; by binding cardiolipin and shielding it from oxidative damage, elamipretide is thought to preserve cristae architecture, improve the coupling efficiency of ATP production, and reduce the leakage of reactive oxygen species from damaged mitochondria. In clinical trials it has been given by subcutaneous injection.
What's it studied for?
Research contexts. Not proven uses, and not recommendations.
Does the human evidence stack up?
Substantial by the standards of peptides sold online, but decidedly mixed. Multiple Phase 2/3 randomised controlled trials exist, and the branded form (Forzinity) received FDA accelerated approval in September 2025 to improve muscle strength in Barth syndrome, based largely on the TAZPOWER programme and its open-label extension. The results across the wider programme are uneven: the Phase 3 MMPOWER-3 trial in primary mitochondrial myopathy missed its co-primary endpoints (6-minute walk distance and fatigue scores), and programmes in heart failure (HFpEF) and dry AMD/geographic atrophy did not succeed. There is NO controlled human evidence for the general anti-ageing, anti-fatigue, exercise-recovery, or 'mitochondrial rejuvenation in healthy people' claims under which it is marketed in the grey market. That case rests entirely on rodent and cell-culture data. The drug has generally been well tolerated in trials, with injection-site reactions the most common issue, but safety data come from sick patient populations over limited durations.
What could go wrong?
- !Marketing mismatch: it is approved only for an ultra-rare disease (Barth syndrome), and only in the US, yet sold online for vague 'longevity', 'anti-ageing' and 'energy' purposes for which there is no human evidence.
- !Accelerated approval means the Barth-syndrome benefit rests on a surrogate endpoint (muscle strength); confirmatory clinical-outcome evidence is still required and the approval could be withdrawn if it is not delivered.
- !Repeated late-stage failures in larger indications (primary mitochondrial myopathy, heart failure, dry AMD) show the mechanism does not reliably translate into clinical benefit in common conditions.
- !Grey-market 'research chemical' SS-31 is unlicensed and unregulated, sold 'not for human consumption'. There is no guarantee of identity, purity, sterility or correct peptide sequence.
- !Injectable use carries infection and injection-site risks when self-administered outside medical supervision.
- !Long-term safety data in healthy people are absent; trial safety data come from sick patients over limited durations.
Is it legal in the UK?
As of mid-2026, elamipretide is NOT a licensed medicine in the UK. The September 2025 Forzinity approval is a US FDA accelerated approval only, with no MHRA marketing authorisation. In the UK it is an investigational/unlicensed drug, and any legitimate clinical use would be through a clinical trial or a 'specials'/named-patient route under specialist supervision. The 'SS-31' sold by online peptide vendors is an unlicensed research chemical, marketed 'not for human consumption' to sidestep medicines law. Supplying or selling it for human use without authorisation would breach the Human Medicines Regulations 2012 and fall foul of the MHRA. It is not an approved over-the-counter or prescription product for ageing, fatigue or performance in the UK.
Key trials
- NCT03098797· Phase 2/3· Completed; basis for FDA accelerated approval (Forzinity, 2025)
TAZPOWER: Elamipretide in Barth syndrome (Phase 2/3 randomised crossover plus open-label extension)
Missed primary endpoints in the crossover phase; the open-label extension reported sustained muscle-strength and cardiac improvements.
- NCT03323749· Phase 3· Completed, failed primary endpoints
MMPOWER-3: Elamipretide in Primary Mitochondrial Myopathy (Phase 3)
No significant benefit on 6-minute walk distance or fatigue; post-hoc nuclear-DNA-variant subgroup signal only.
Sources
- 01A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome, a genetic disorder of mitochondrial cardiolipin metabolism (TAZPOWER) — Reid Thompson W, et al., Genetics in Medicine (2021)
Key Barth syndrome trial: missed primary endpoints in the randomised crossover phase but the open-label extension showed durable functional/cardiac gains; underpinned the later approval.
- 02Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial — Karaa A, et al., Neurology (2023)
Phase 3 (n=218) that FAILED its co-primary endpoints (6MWT, PMMSA fatigue). It is an important counterweight to the hype; a post-hoc nuclear-DNA-variant subgroup signalled possible benefit.
- 03FDA Grants Accelerated Approval to First Treatment for Barth Syndrome (FORZINITY / elamipretide), U.S. Food and Drug Administration press announcement (2025)
Documents the September 2025 accelerated approval and its limited, surrogate-endpoint-based scope (improvement in muscle strength).
- 04Elamipretide: A Review of Its Structure, Mechanism of Action, and Therapeutic Potential, International Journal of Molecular Sciences (2025)
Recent mechanistic review covering cardiolipin binding, cristae stabilisation and the clinical landscape.
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