At a glance: SS-31 is a tiny four-amino-acid peptide that travels into mitochondria, the cell's energy factories, and stabilizes their inner membrane. Under the name elamipretide, it received FDA accelerated approval in September 2025 as Forzinity, the first treatment for Barth syndrome, a rare inherited mitochondrial disease. Results in other conditions have been mixed: a phase 3 trial in mitochondrial muscle disease missed its goals. The approved drug is a prescription for Barth syndrome only; SS-31 sold online for anti-aging or performance is unregulated.
What is SS-31?
SS-31 is a synthetic tetrapeptide (D-Arg-Dmt-Lys-Phe-NH2) from the "Szeto-Schiller" family of peptides, named after the researchers who designed them. Its drug name is elamipretide, developed by Stealth BioTherapeutics, and it has also been called Bendavia and MTP-131.
Its alternating positive charges and water-repelling groups let it slip through cell membranes and concentrate inside mitochondria without needing energy to get there.
How does SS-31 work?
- Binds cardiolipin: a fat found almost only in the inner mitochondrial membrane, where the energy-making machinery sits
- Stabilizes energy production: by protecting cardiolipin, it helps keep the electron transport chain organized and efficient
- Reduces oxidative stress: it lowers harmful reactive oxygen species made by damaged mitochondria
- Protects stressed mitochondria: in lab studies it prevented mitochondrial swelling and breakdown under stress, while leaving healthy mitochondria largely unaffected
What the research shows
| Study | Who was studied | Main finding |
|---|---|---|
| TAZPOWER (Barth syndrome) | 12 males with Barth syndrome; 12-week placebo-controlled phase, then open-label extension | No benefit in the 12-week phase; knee-muscle strength improved over years of treatment, the basis of 2025 FDA accelerated approval |
| MMPOWER-3 (phase 3, 2019) | Adults with primary mitochondrial myopathy | Missed its main goals: no improvement in 6-minute walk or fatigue vs placebo |
| EVOLVE (phase 2a, 2016) | 14 people having stents placed in narrowed kidney arteries; single dose | Kidney blood flow and function improved at 3 months in the treated group (company-reported) |
| MOTION (phase 2) | 40 adults aged 60 to 85 | Muscle energy production rose more than placebo, but not significantly, and the effect faded within a week |
| Animal and cell studies | Kidney, heart, brain, eye and aging models | Broad protection against injury and age-related decline; reviewed by Zhu et al., 2022 |
A 2022 review of SS-31 in kidney disease concluded that it is promising in animal models, but human evidence is scarce and its exact mechanism in kidney disease is still unclear.
Why it gets attention
- Mitochondria and aging: declining mitochondrial function is linked to aging, so SS-31 is popular in longevity circles
- A real approval: Forzinity's 2025 approval made it one of the few mitochondria-targeting drugs to reach the market
- Organ protection research: studied for kidney, heart and eye disease, including heart failure and dry age-related macular degeneration
- Gray-market availability: sold online as a "research peptide" for energy, endurance and recovery
How it is used
Forzinity is a prescription injection under the skin, given once daily, approved for people with Barth syndrome who weigh at least 30 kg. It is not approved for newborns because the formulation contains benzyl alcohol. Online SS-31 is a different, unregulated product with no established dose for any other use. This page does not provide dosing guidance.
What about side effects?
From the FDA approval and trial reports:
- Injection-site reactions: the most common side effect, including redness, hardening, itching and pain. In the Barth syndrome extension study, 2 of 10 participants stopped because of them.
- Allergic reactions: serious hypersensitivity reactions have been reported.
- Slow benefit: in Barth syndrome, measurable strength gains appeared only after long-term treatment.
- Unknowns: long-term safety in healthy people has not been studied, and unregulated products may be impure or mislabeled.
Regulatory status
- FDA accelerated approval (September 19, 2025) as Forzinity to improve muscle strength in patients with Barth syndrome weighing at least 30 kg. The approval was based on improved knee-muscle strength, and Stealth must run a confirmatory placebo-controlled trial to show real-world benefit.
- Not approved for mitochondrial myopathy, kidney disease, heart failure, eye disease, aging or performance.
- Products sold online as "SS-31" for research are not the approved drug and are not intended for human use.
The bottom line
SS-31 is a genuinely innovative drug that targets the energy machinery inside cells, and it has become an approved, if narrowly used, treatment for Barth syndrome. Beyond that, the story is mixed: strong animal data, but a failed phase 3 trial in mitochondrial muscle disease and only small human studies in other conditions. There is no good evidence that it slows aging or boosts performance in healthy people.
Frequently asked questions
What is SS-31?
A four-amino-acid peptide that targets the inner membrane of mitochondria, the parts of cells that make energy.
How is SS-31 taken?
Daily subcutaneous injection.
Is SS-31 FDA approved?
FDA accelerated approval (September 2025) for Barth syndrome, in patients weighing at least 30 kg.
What has research shown about SS-31?
- Barth syndrome, a rare mitochondrial disease, in clinical trials.
- Mitochondrial muscle diseases and heart failure in other trials.
What side effects have been reported?
- Injection site redness (100% in the controlled study)
- Injection site pain (75%)
- Injection site hardening (67%)
- Injection site itching (67%)
- Injection site bruising (25%)
Serious or less common risks are listed in the Side Effects section above.
What is still unknown about its safety?
Side effects that are rare, or that only appear after many years of use, are still being tracked through post-marketing surveillance. Talk to a prescriber about your own risk.
References
- Zhu Y, et al. SS-31, a mitochondria-targeting peptide, ameliorates kidney disease. Oxidative Medicine and Cellular Longevity. 2022. View source
- FDA: FDA grants accelerated approval to first treatment for Barth syndrome (September 2025). View source
- Clinician.com: Elamipretide injection (Forzinity), drug review including TAZPOWER results. View source
- BioSpace: Stealth Bio's elamipretide fails mitochondrial myopathy trial (MMPOWER-3, December 2019). View source
- Drug Development and Delivery: Stealth BioTherapeutics announces phase II findings in renal artery stenosis (EVOLVE, 2016). View source
- Lifespan.io: Stealth BioTherapeutics, Forzinity (elamipretide) development roadmap. View source