SS-31
Also known as: Elamipretide, MTP-131, Bendavia, Forzinity
FDA-approved (accelerated approval, September 2025) under the brand name Forzinity, specifically to improve muscle strength in adults and children with Barth syndrome who weigh at least 30 kg. All other uses discussed on this page remain investigational/research-only.
5 notable studies · 7 references
TLDR
SS-31 (elamipretide) is a cardiolipin-targeting mitochondrial peptide studied across mitochondrial, muscular, cardiovascular, and ocular disorders, with FDA accelerated approval as Forzinity to improve muscle strength in Barth syndrome patients weighing at least 30 kg.
Research Supports
- FDA-approved (Forzinity) for improving muscle strength in Barth syndrome, a specific genetic mitochondrial disorder
- Studied for interaction with cardiolipin in the inner mitochondrial membrane
- Investigated in controlled human trials for primary mitochondrial myopathy and Barth syndrome
- Research continuing into cardiovascular, ocular, and aging-related mitochondrial dysfunction outside the approved indication
Observations Reported in Research
- MMPOWER trial (2018): early dose-escalation study established elamipretide could be safely administered to adults with primary mitochondrial myopathy
- Barth syndrome Phase 2/3 trial (2021): randomized portion did not meet its primary endpoints, but the open-label extension reported improvements in six-minute walk distance, symptom scores, and knee-extensor strength
- Later mitochondrial-myopathy studies did not uniformly reproduce early functional findings
These are brief summaries of what the referenced research examined or reported — not conclusions about safety or effectiveness, and not medical advice. See Notable Studies and Sources & References below for the full context and citations.
At a Glance
Classification: Mitochondria-targeting aromatic-cationic tetrapeptide; mitochondrial cardiolipin-binding peptide
SS-31, better known clinically as elamipretide, is a mitochondria-targeting tetrapeptide studied for its ability to interact with cardiolipin in the inner mitochondrial membrane and influence mitochondrial structure, bioenergetics, and cellular stress. Unlike many compounds commonly discussed in research-peptide circles, elamipretide has reached clinical approval. In September 2025, the U.S. Food and Drug Administration granted accelerated approval to elamipretide under the brand name Forzinity to improve muscle strength in adults and children with Barth syndrome who weigh at least 30 kg. Research outside that specific approved indication continues across mitochondrial disease, skeletal muscle dysfunction, cardiovascular disease, ocular disease, aging-related mitochondrial dysfunction, and other conditions associated with impaired mitochondrial function.
What Is SS-31?
SS-31 is a small synthetic peptide composed of four amino acids. It was developed to selectively concentrate at the inner mitochondrial membrane, an important structure involved in cellular energy production. The compound is now generally referred to in clinical research as elamipretide. Its mitochondrial target is especially important because the inner mitochondrial membrane contains cardiolipin, a specialized phospholipid that helps organize membrane structure, respiratory-chain proteins, and the cristae where much of mitochondrial energy production occurs. Rather than simply functioning as a conventional antioxidant, current research suggests that elamipretide interacts with cardiolipin and alters the physical and functional environment of the inner mitochondrial membrane. This may help stabilize mitochondrial architecture and improve aspects of energy production under conditions of mitochondrial dysfunction. Elamipretide has been investigated in numerous preclinical models and human clinical trials. In September 2025, the FDA granted accelerated approval to Forzinity (elamipretide) for improving muscle strength in adults and pediatric patients with Barth syndrome weighing at least 30 kg. This approval applies to that specific indication and population.
What Are Researchers Studying?
Barth syndrome
Barth syndrome is a rare genetic mitochondrial disorder involving abnormal cardiolipin remodeling. Because elamipretide interacts with cardiolipin and the inner mitochondrial membrane, Barth syndrome became one of its most important clinical research areas. Clinical trials have examined physical function, fatigue, muscle strength, cardiac measures, and biomarkers in people with Barth syndrome. In 2025, elamipretide received FDA accelerated approval under the brand Forzinity to improve muscle strength in Barth syndrome patients weighing at least 30 kg. Continued confirmatory research is required as part of the accelerated approval.
Primary mitochondrial myopathy
Researchers have investigated elamipretide in people with primary mitochondrial myopathy, a group of genetic mitochondrial disorders that can produce muscle weakness, fatigue, and exercise intolerance. Early clinical studies examined exercise performance and safety, but results across the clinical development program have been mixed. This remains distinct from the approved Barth syndrome indication.
Mitochondrial structure and bioenergetics
A major focus of SS-31 research is how interactions with cardiolipin affect mitochondrial structure and energy production. Researchers have studied effects on mitochondrial cristae, membrane organization, respiratory-chain function, ATP production, oxidative stress, and the organization of cardiolipin-dependent proteins.
Skeletal muscle function
Elamipretide has been investigated for mitochondrial dysfunction associated with skeletal-muscle weakness and impaired exercise capacity. Research ranges from mechanistic animal experiments to clinical studies in mitochondrial diseases. Evidence varies considerably depending on the disease and outcome being studied.
Cardiovascular function
Because heart muscle has exceptionally high energy requirements, researchers have investigated elamipretide in several cardiovascular settings, including heart failure and ischemia-reperfusion injury. Preclinical findings have frequently been encouraging, but clinical translation has varied by condition and trial.
Ocular and age-related mitochondrial dysfunction
Elamipretide has also been studied in ocular disorders and experimental models involving age-associated mitochondrial decline.
How Does It Work?
Elamipretide selectively targets the inner mitochondrial membrane, where it interacts with cardiolipin. Cardiolipin is an unusual phospholipid found predominantly in this membrane. It contributes to mitochondrial membrane organization, cristae architecture, respiratory-chain function, and the organization of proteins involved in cellular energy production. Earlier explanations of SS-31 often emphasized antioxidant activity and direct scavenging of reactive oxygen species. More recent research has produced a more detailed picture. Current evidence suggests that elamipretide's interaction with cardiolipin can influence membrane electrostatic properties and the organization of cardiolipin-dependent proteins. These changes may help stabilize mitochondrial structure, improve respiratory-chain efficiency, support ATP production, and reduce excessive mitochondrial reactive oxygen species generation. In other words, researchers increasingly view SS-31 not simply as an antioxidant, but as a compound that modifies the physical and functional environment of the inner mitochondrial membrane. The exact consequences vary by tissue, disease state, and experimental model, and the complete mechanism remains an active area of research.
What Does the Research Show?
Human research
SS-31/elamipretide has considerably more human research than many experimental peptides. Clinical development has included studies in Barth syndrome, primary mitochondrial myopathy, heart disease, and ocular disorders, among other areas. The strongest regulatory evidence currently concerns Barth syndrome. The TAZPOWER program included a randomized, double-blind, placebo-controlled crossover study followed by long-term open-label treatment. The initial randomized portion did not meet its primary endpoints of improvement in six-minute walk distance and Barth Syndrome Symptom Assessment scores. During longer open-label treatment, investigators reported improvements in measures including walking distance, fatigue, muscle strength, and some cardiac parameters. Interpretation is limited by the very small number of patients and the absence of a concurrent placebo group during the long-term extension. The FDA subsequently evaluated a broader body of evidence and in September 2025 granted accelerated approval to Forzinity for improving muscle strength in Barth syndrome patients weighing at least 30 kg. The approval was based on improvement in knee-extensor muscle strength, which the FDA considered reasonably likely to predict clinical benefit. A post-approval randomized, double-blind, placebo-controlled confirmatory trial is required to determine whether the muscle-strength improvement translates into patient benefit.
Animal research
SS-31/elamipretide has considerably more human research than many experimental peptides. Clinical development has included studies in Barth syndrome, primary mitochondrial myopathy, heart disease, and ocular disorders, among other areas. The strongest regulatory evidence currently concerns Barth syndrome. The TAZPOWER program included a randomized, double-blind, placebo-controlled crossover study followed by long-term open-label treatment. The initial randomized portion did not meet its primary endpoints of improvement in six-minute walk distance and Barth Syndrome Symptom Assessment scores. During longer open-label treatment, investigators reported improvements in measures including walking distance, fatigue, muscle strength, and some cardiac parameters. Interpretation is limited by the very small number of patients and the absence of a concurrent placebo group during the long-term extension. The FDA subsequently evaluated a broader body of evidence and in September 2025 granted accelerated approval to Forzinity for improving muscle strength in Barth syndrome patients weighing at least 30 kg. The approval was based on improvement in knee-extensor muscle strength, which the FDA considered reasonably likely to predict clinical benefit. A post-approval randomized, double-blind, placebo-controlled confirmatory trial is required to determine whether the muscle-strength improvement translates into patient benefit.
In-vitro research
Cellular and biochemical experiments have been central to understanding SS-31. Research has examined its interaction with cardiolipin, mitochondrial membrane properties, respiratory-chain proteins, electron transport, ATP production, reactive oxygen species generation, and mitochondrial cristae organization.These studies helped shift the proposed mechanism away from a simple antioxidant explanation toward a model in which elamipretide modifies the cardiolipin-rich inner mitochondrial membrane and the organization and performance of proteins operating within it.
Notable Studies
Randomized Dose-Escalation Trial of Elamipretide in Adults With Primary Mitochondrial Myopathy
humanThe MMPOWER study evaluated intravenous elamipretide in 36 adults with genetically confirmed primary mitochondrial myopathy. Researchers investigated safety, tolerability, and effects on exercise performance. The study provided early controlled human evidence that elamipretide could be administered to patients with mitochondrial disease and explored whether mitochondrial targeting could translate into measurable functional changes. The trial helped establish the basis for larger clinical studies of elamipretide in primary mitochondrial myopathy.
Limitations: The trial was small, short in duration, and designed as an early dose-escalation study. Findings from a limited number of participants cannot establish long-term effectiveness or safety. Later clinical studies of primary mitochondrial myopathy have not uniformly reproduced promising early functional findings, emphasizing the difficulty of translating mitochondrial mechanisms into clinical outcomes.
View publication →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
humanResearchers evaluated daily elamipretide in patients with Barth syndrome, a mitochondrial disorder involving abnormal cardiolipin metabolism. Twelve participants entered the randomized crossover portion of the study. The randomized portion did not meet either primary endpoint: improvement in the six-minute walk test or the Barth Syndrome Symptom Assessment scale. Ten participants subsequently entered an open-label extension. After longer exposure, researchers reported improvements in six-minute walk distance, symptom scores, knee-extensor strength, patient-reported outcomes, and some cardiac measures. The study became an important component of the clinical evidence supporting continued development of elamipretide for Barth syndrome.
Limitations: Barth syndrome is extremely rare, resulting in a very small study population. Neither primary endpoint was met during the randomized placebo-controlled portion of the study. Improvements observed later occurred during an open-label extension without a concurrent placebo group, making causal interpretation more difficult. The findings therefore required consideration alongside additional longitudinal, natural-history, mechanistic, and regulatory evidence.
View publication →Long-Term Efficacy and Safety of Elamipretide in Patients With Barth Syndrome: 168-Week Open-Label Extension Results of TAZPOWER
humanResearchers followed participants from the TAZPOWER program during prolonged treatment with elamipretide. Ten patients entered the open-label extension and eight reached the 168-week assessment. Investigators reported sustained improvements from open-label-extension baseline in six-minute walk distance, with a cumulative improvement of approximately 96 meters at week 168. Fatigue scores remained below baseline, and investigators reported favorable trends in several cardiac measures. Injection-site reactions were the most common adverse events.
Limitations: The study involved an exceptionally small population and lacked a concurrent placebo group during the long-term extension. Open-label studies are vulnerable to expectancy effects, changes in supportive care, regression to the mean, survivor effects, and other sources of bias. The findings are important in the context of a rare disease but cannot be interpreted like results from a large randomized controlled trial.
View publication →Contemporary Insights Into Elamipretide's Mitochondrial Mechanism of Action and Therapeutic Effects
in-vitroThis review synthesized newer evidence regarding how elamipretide interacts with the inner mitochondrial membrane. The authors described evidence supporting cardiolipin binding and discussed how elamipretide may influence mitochondrial membrane electrostatic properties, cardiolipin-dependent protein organization, mitochondrial structure, and bioenergetics. The review also examined preclinical findings and clinical experience in Barth syndrome, primary mitochondrial myopathy, and age-related macular degeneration. It reflects the evolution of the proposed mechanism from a relatively simple antioxidant model toward direct modulation of mitochondrial membrane organization and function.
Limitations: This is a review rather than a new controlled experiment. Its conclusions synthesize studies of very different types, ranging from molecular experiments and animal models to small clinical trials. Mechanistic plausibility and preclinical efficacy should not be treated as equivalent to demonstrated clinical benefit.
View publication →FDA Evaluation Supporting Accelerated Approval of Forzinity (Elamipretide) for Barth Syndrome
in-vitroThe FDA reviewed clinical and supporting evidence for elamipretide in Barth syndrome. On September 19, 2025, the agency granted accelerated approval to Forzinity to improve muscle strength in adults and pediatric patients with Barth syndrome weighing at least 30 kg. The approval was based on improvement in knee-extensor muscle strength. The FDA determined that this measure was reasonably likely to predict clinical benefit, such as improved ability to stand or walk farther. Forzinity became the first FDA-approved treatment for Barth syndrome.
Limitations: Accelerated approval differs from traditional approval based directly on demonstrated clinical outcomes. The FDA is requiring a post-approval randomized, double-blind, placebo-controlled trial to confirm that improvements in muscle strength translate into patient benefit. The approved indication is specifically Barth syndrome in patients meeting the labeled weight criterion and does not establish effectiveness for other proposed applications of SS-31/elamipretide.
View publication →What We Still Don't Know
Despite extensive research and an FDA-approved indication, many questions surrounding elamipretide remain. Important areas of ongoing research include: Whether benefits observed in Barth syndrome extend to other mitochondrial diseases Which forms of mitochondrial dysfunction are most responsive to cardiolipin-targeted therapy Whether promising findings from animal models translate into meaningful clinical benefits in other diseases The long-term clinical impact of treatment beginning at different ages How changes in mitochondrial structure and bioenergetics translate into patient-relevant outcomes Whether elamipretide has clinically meaningful effects in age-related mitochondrial dysfunction Which biomarkers best predict treatment response Whether improvements in knee-extensor strength in Barth syndrome translate into broader functional benefits For its approved Barth syndrome indication, confirmatory clinical research remains required following accelerated approval.
Recent publications
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Sources & References
- Karaa A, Haas R, Goldstein A, et al. Randomized Dose-Escalation Trial of Elamipretide in Adults With Primary Mitochondrial Myopathy. Neurology. 2018;90(14). doi:10.1212/WNL.0000000000005255.
- Reid Thompson W, Hornby B, Manuel R, et al. 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. Genetics in Medicine. 2021.
- Reid Thompson W, et al. Long-Term Efficacy and Safety of Elamipretide in Patients With Barth Syndrome: 168-Week Open-Label Extension Results of TAZPOWER. Molecular Genetics and Metabolism. 2024.
- Sabbah HN, Alder NN, Sparagna GC, et al. Contemporary Insights Into Elamipretide's Mitochondrial Mechanism of Action and Therapeutic Effects. Biomedicine & Pharmacotherapy. 2025;187:118056. doi:10.1016/j.biopha.2025.118056.
- Elsharkawi I, et al. Elamipretide in the Management of Barth Syndrome: Current Evidence and a Case Report. 2025.
- U.S. Food and Drug Administration. FDA Grants Accelerated Approval to First Treatment for Barth Syndrome. September 19, 2025.
- U.S. Food and Drug Administration. Drug Trials Snapshots: Forzinity (elamipretide). 2025.
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