SS-31

What it is

SS-31 is a four amino acid peptide that concentrates in the inner mitochondrial membrane, where it binds cardiolipin. Cardiolipin is a phospholipid unique to that membrane and essential to organising the electron transport chain. When cardiolipin is damaged or abnormal, respiration becomes inefficient and leaks reactive oxygen species.

SS-31 stabilises it. That is an unusually specific mechanism for something marketed under the longevity banner, and it is why the compound made it through real drug development.

What the approval actually covers

In September 2025 the FDA granted accelerated approval to elamipretide as Forzinity, to improve muscle strength in adults and children with Barth syndrome weighing at least 30 kg. Barth syndrome is an ultra-rare X-linked disorder in which the gene responsible for remodelling cardiolipin is defective, which makes it the single condition where SS-31's mechanism maps exactly onto the pathology.

It is the first FDA-approved mitochondria-targeted therapeutic, which is a genuine milestone.

The path there was not smooth. In October 2024 FDA staff stated the available evidence did not establish effectiveness. An advisory committee then voted 10 to 6 in favour, and the agency later agreed to consider knee extensor strength as an intermediate endpoint supporting accelerated approval, on the basis of its correlation with the six minute walk test.

Accelerated approval on an intermediate endpoint means confirmatory evidence of clinical benefit is still owed.

The trials that did not work are the relevant ones for everyone else

Most people interested in SS-31 do not have Barth syndrome. They have read that it repairs mitochondria.

The programme tested that broader premise repeatedly. Trials in primary mitochondrial myopathy, including MMPOWER-3, and studies in eye disease and heart failure largely missed their primary endpoints. The compound was safe in those trials and it did not demonstrate the benefit being sought.

So the honest summary is narrow and specific: SS-31 works well enough for a disease of cardiolipin remodelling to earn accelerated approval, and it has repeatedly failed to show benefit in conditions where mitochondrial dysfunction is present but not the primary defect. General age-related mitochondrial decline is further from Barth syndrome than any of the indications that failed.

Practical notes

• The mechanism is real and the generalisation is not. A drug that fixes a specific lipid defect is not a mitochondrial tune-up.
• Injection-site reactions dominated the safety profile. They are the most common reason people stop.
• Approved product and research vial are different things. Forzinity is a manufactured pharmaceutical with an accelerated approval and a confirmatory obligation. A lyophilised vial from a peptide supplier shares a sequence and nothing else.

Side effects and warning signs

Commonly reported

• Injection-site reactions, which are common and were the most frequent adverse event across trials
• Headache
• Nausea
• Dizziness

Stop and get medical help

• Severe or spreading injection-site reaction
• The approval is accelerated and based on an intermediate endpoint, so confirmatory evidence of clinical benefit is still outstanding

Sources

1. Elamipretide: a mitochondria-targeting drug for Barth syndrome, Trends in Pharmacological Sciences 2026review
2. Elamipretide drug development record, Friedreich's Ataxia Research Allianceregulatory

From the community

Discussion for this compound concentrates in r/longevity and r/Peptides.

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