SS-31 (Elamipretide)

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.

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.

Research contexts. Not proven uses, and not recommendations.

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.

• !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.

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.

• 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· Terminated: the double-blind part did not meet its 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.

1. 01
   A 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.

2. 02
   Efficacy 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.

3. 03
   FDA 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).

4. 04
   Elamipretide: 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.