What Is SS-31?
SS-31 is a synthetic four-amino-acid peptide developed specifically to target mitochondria.
It is also known as:
Elamipretide
Bendavia
MTP-131
Forzinity
What makes SS-31 unusual is that it does not simply enter cells and act somewhere in the cytoplasm.
It preferentially localizes to the inner mitochondrial membrane.
There, it interacts with a specialized phospholipid called cardiolipin.
That gives SS-31 a very different research profile from metabolic peptides such as GLP-1 agonists or growth-hormone secretagogues.
Its central target is mitochondrial function itself.
Why Are Researchers Interested in It?
Mitochondria do much more than produce energy.
They are involved in:
ATP production, oxidative stress, apoptosis, calcium handling, metabolic signaling, and cellular stress responses.
Mitochondrial dysfunction has been linked with:
rare genetic disease, heart failure, skeletal-muscle dysfunction, neurodegeneration, kidney disease, metabolic disease, and aspects of aging.
SS-31 attracted attention because it was designed to interact directly with mitochondrial membrane biology rather than simply treating downstream symptoms.
That makes it one of the most important examples of a true mitochondria-targeted peptide.
How Does SS-31 Work?
SS-31 binds to cardiolipin.
Cardiolipin is a unique phospholipid found primarily in the inner mitochondrial membrane.
It helps organize and stabilize many of the protein complexes responsible for oxidative phosphorylation.
These proteins include components of the electron transport chain.
When cardiolipin becomes damaged or improperly remodeled, mitochondrial energy production can become less efficient.
Elamipretide is believed to associate with cardiolipin and improve organization of the inner mitochondrial membrane, supporting more efficient electron transport and reducing excess production of reactive oxygen species.
What Is Cardiolipin?
Cardiolipin is one of the defining molecules of mitochondrial membranes.
It helps maintain the structure and function of mitochondrial respiratory-chain complexes.
These complexes are responsible for converting nutrients into usable cellular energy.
Cardiolipin also participates in:
mitochondrial membrane structure, respiratory-chain organization, apoptosis signaling, and mitochondrial protein interactions.
Because cardiolipin is so central to mitochondrial function, problems involving cardiolipin can have major consequences in tissues with high energy demand.
These include:
heart muscle, skeletal muscle, brain, kidneys, and other metabolically active tissues.
ATP & Cellular Energy
ATP is the primary energy currency used by cells.
Most ATP is generated through oxidative phosphorylation inside mitochondria.
The electron transport chain creates an electrochemical gradient.
ATP synthase then uses that gradient to produce ATP.
If mitochondrial membranes are damaged or the electron transport chain becomes inefficient, cells may struggle to meet their energy demands.
SS-31 research has therefore focused heavily on whether improving mitochondrial membrane function can improve ATP production and cellular performance.
Reactive Oxygen Species
Mitochondria naturally generate reactive oxygen species, or ROS.
Small amounts of ROS participate in normal signaling.
Excessive ROS, however, can damage:
lipids, proteins, DNA, and mitochondrial membranes.
Damaged mitochondria can then generate even more ROS.
This can create a self-reinforcing cycle of mitochondrial dysfunction.
Elamipretide has been studied for its ability to improve mitochondrial efficiency and reduce excessive oxidative stress rather than functioning simply as a traditional antioxidant.
That distinction matters.
The goal is not necessarily to neutralize every free radical.
The goal is to improve how the mitochondria generate energy in the first place.
Barth Syndrome
Barth syndrome is where SS-31 research ultimately reached FDA approval.
Barth syndrome is a rare X-linked mitochondrial disorder caused by mutations in the TAZ gene.
TAZ encodes tafazzin, an enzyme involved in cardiolipin remodeling.
When tafazzin does not function properly, mature cardiolipin levels and structure become abnormal.
This can severely impair mitochondrial function.
Barth syndrome commonly involves:
cardiomyopathy, skeletal-muscle weakness, exercise intolerance, fatigue, growth problems, and neutropenia.
Because the disorder directly involves cardiolipin biology, elamipretide was a particularly logical therapeutic candidate.
FDA Approval
On September 19, 2025, the FDA granted accelerated approval to Forzinity, the pharmaceutical form of elamipretide.
The approved indication is:
to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg.
This was the first FDA-approved treatment specifically for Barth syndrome.
Forzinity is administered by subcutaneous injection once daily.
The FDA-approved dose for patients weighing at least 30 kg is 40 mg daily.
Why Was Approval Accelerated?
Forzinity received accelerated approval based on improvement in knee-extensor muscle strength.
Accelerated approval allows the FDA to approve treatments for serious conditions based on an intermediate endpoint that is reasonably likely to predict clinical benefit.
Continued approval depends on confirmation of that benefit in additional research.
The FDA has required a randomized, double-blind, placebo-controlled confirmatory trial in patients five years and older with Barth syndrome.
This means Forzinity is genuinely FDA approved, but the approval remains tied to ongoing verification of clinical benefit.
Clinical Research in Barth Syndrome
The original randomized Phase 2/3 Barth syndrome study was small because Barth syndrome itself is extremely rare.
Twelve participants entered the randomized crossover study.
The initial blinded phase did not meet its primary endpoints for six-minute walking distance or symptom scores.
However, the open-label extension produced a different picture.
By 36 weeks, researchers reported improvements in walking distance, symptoms, muscle strength, and some cardiac measures.
This led researchers to investigate whether meaningful effects might require longer treatment.
Long-Term Results
Long-term follow-up became especially important for elamipretide.
In the extended Barth syndrome study, ten participants entered the open-label extension and eight remained through 168 weeks.
Researchers reported sustained improvements in:
six-minute walk performance, fatigue scores, muscle strength, several cardiac measurements, and cardiolipin-related biomarkers.
At week 168, the average improvement in six-minute walk distance compared with extension baseline was about 96 meters.
These longer-term findings helped support continued development of elamipretide.
Muscle Strength
Muscle weakness is a major problem in Barth syndrome.
Skeletal muscle requires enormous amounts of ATP.
When mitochondrial function is impaired, muscles can fatigue rapidly and struggle to generate normal force.
The FDA approval of Forzinity is specifically based around improvement in muscle strength.
This creates a direct link between mitochondrial function and a clinically measurable physical outcome.
Rather than simply improving a laboratory biomarker, the goal is to improve what mitochondria allow muscles to actually do.
Fatigue
Fatigue is one of the most obvious symptoms of impaired mitochondrial energy production.
Cells may have enough oxygen and nutrients but still struggle to convert them efficiently into usable energy.
Barth syndrome studies reported improvements in fatigue during longer-term elamipretide treatment.
Fatigue research has also contributed to interest in elamipretide beyond Barth syndrome.
However, the FDA approval does not extend to general fatigue.
Cardiovascular Research
The heart is one of the most mitochondria-rich organs in the body.
Cardiac muscle contracts continuously and therefore requires an enormous and constant supply of ATP.
Mitochondrial dysfunction can contribute to:
cardiomyopathy, impaired contractility, oxidative stress, and heart failure.
Barth syndrome frequently produces serious cardiomyopathy because defective cardiolipin disrupts mitochondrial energy production within cardiac muscle.
This is why elamipretide has been studied extensively in cardiovascular research.
Heart Failure Research
Before approval for Barth syndrome, elamipretide was investigated in broader heart-failure research.
The underlying hypothesis was straightforward:
if mitochondrial dysfunction contributes to heart failure, improving mitochondrial membrane function might improve cardiac energetics.
Animal studies were particularly encouraging.
Human trials produced more mixed results.
That does not invalidate the mitochondrial mechanism, but it shows that improving cellular energetics does not automatically translate into large clinical improvements across every type of heart disease.
Different diseases can involve mitochondrial dysfunction for very different reasons.
Skeletal Muscle Research
Skeletal muscle also contains large numbers of mitochondria.
Exercise requires rapid ATP production.
Researchers have therefore studied SS-31 in areas involving:
muscle endurance, mitochondrial myopathy, exercise intolerance, muscle aging, and recovery.
The Barth syndrome approval now provides strong proof that mitochondrial targeting can produce measurable muscle-strength effects in at least one specific mitochondrial disorder.
That makes broader skeletal-muscle research especially interesting.
Mitochondrial Disease
Barth syndrome is only one mitochondrial disease.
Researchers have investigated elamipretide in several other conditions involving mitochondrial dysfunction.
The broader scientific question is whether cardiolipin stabilization can help mitochondrial disorders even when cardiolipin itself is not the primary genetic defect.
That remains an active research area.
Forzinity’s approval provides an important proof of concept:
directly targeting mitochondrial membrane biology can produce a clinically useful therapy.
Aging & Mitochondria
Mitochondrial function tends to decline with age.
Age-related changes can include:
reduced respiratory efficiency, altered mitochondrial dynamics, increased oxidative stress, accumulated mitochondrial DNA damage, and impaired mitophagy.
These changes have led to interest in SS-31 as a potential tool for studying healthy aging.
Animal research has explored effects on:
muscle function, cardiovascular performance, kidney function, eye health, and other age-associated systems.
This is one of the main reasons SS-31 is widely discussed within longevity research.
Does SS-31 Reverse Mitochondrial Aging?
That would be too strong a conclusion.
Aging involves many interacting systems beyond mitochondrial dysfunction.
SS-31 has produced interesting results in experimental aging models, but Forzinity is not FDA approved as an anti-aging drug.
The stronger interpretation is:
SS-31 gives researchers a way to test what happens when age-associated mitochondrial dysfunction is directly targeted.
That is already scientifically valuable.
Kidney Research
The kidneys require substantial mitochondrial energy, particularly in tubular cells responsible for transporting electrolytes and nutrients.
Mitochondrial dysfunction can contribute to kidney injury.
Elamipretide has therefore been investigated in experimental and clinical renal research.
Areas of interest have included:
ischemic kidney injury, renal artery stenosis, chronic kidney dysfunction, and mitochondrial remodeling.
Results have varied depending on the condition.
This reinforces the idea that mitochondrial dysfunction is not a single disease process.
Eye & Retinal Research
Retinal cells also have extremely high energy requirements.
Mitochondrial dysfunction contributes to several retinal and optic-nerve disorders.
Elamipretide has therefore been investigated in ophthalmic research, including mitochondrial eye disease and age-related visual dysfunction.
This is another example of the peptide being studied most intensely in tissues that depend heavily on mitochondrial ATP production.
Neurological Research
The brain consumes a tremendous amount of energy.
Neurons are therefore particularly vulnerable to mitochondrial dysfunction.
Preclinical SS-31 research has explored:
neuroprotection, ischemic brain injury, neurodegeneration, oxidative stress, and mitochondrial dysfunction.
However, its strongest human clinical development has not been in neurological disease.
Neurological applications remain investigational.
SS-31 vs. MOTS-c
SS-31 and MOTS-c are both associated with mitochondria, but they are very different peptides.
SS-31 is a synthetic mitochondria-targeting peptide that binds cardiolipin.
MOTS-c is a naturally occurring mitochondrial-derived peptide that acts more like a signaling molecule involved in metabolic adaptation.
In simplified terms:
SS-31 targets mitochondrial structure and membrane function.
MOTS-c targets mitochondrial-to-cell signaling and metabolic regulation.
That makes them complementary research concepts rather than interchangeable compounds.
SS-31 vs. NAD+
NAD+ is a cellular coenzyme deeply involved in mitochondrial metabolism and redox reactions.
SS-31 is a peptide that physically targets the inner mitochondrial membrane.
Both are relevant to energy metabolism, but they act at very different levels.
NAD+ participates in biochemical reactions throughout the cell.
SS-31 focuses more directly on mitochondrial membrane organization and cardiolipin interactions.
Evidence Snapshot
Mechanistic evidence: Strong. Elamipretide’s cardiolipin-binding mechanism is well characterized.
Mitochondrial research: Extensive across cell, animal, and human research.
Barth syndrome human evidence: Meaningful, though based on a very small population because the disease is exceptionally rare.
Long-term Barth syndrome evidence: Encouraging sustained improvements in walking performance, fatigue, muscle strength, cardiac parameters, and biomarkers.
FDA regulatory evidence: Strong. Elamipretide is FDA approved as Forzinity for a specific Barth syndrome population.
General anti-aging, fatigue, cardiovascular, neurological, or performance uses: Investigational and not part of the FDA-approved indication.
What Do We Know?
We now know something especially important about SS-31:
mitochondria-targeted peptide therapy can work well enough clinically to receive FDA approval.
That is a major milestone.
Elamipretide binds cardiolipin in the inner mitochondrial membrane and influences mitochondrial energetics.
Long-term research in Barth syndrome demonstrated improvements in several functional outcomes.
And in 2025 the FDA concluded that the muscle-strength evidence was sufficient for accelerated approval in a defined Barth syndrome population.
This places elamipretide in a very different scientific category from purely experimental “mitochondrial peptides.”
What Are Researchers Still Trying to Determine?
Researchers still need to establish the full magnitude and durability of clinical benefit in Barth syndrome.
The FDA-required confirmatory trial is designed to address that question.
Beyond Barth syndrome, researchers are investigating whether mitochondrial cardiolipin targeting can meaningfully improve other conditions involving mitochondrial dysfunction.
Important areas include:
other mitochondrial diseases, heart disease, skeletal-muscle dysfunction, kidney disease, neurological disease, age-associated mitochondrial decline, fatigue, and metabolic dysfunction.
The larger question is fascinating:
How many diseases can be improved by repairing mitochondrial energetics rather than treating downstream symptoms?
Research & Regulatory Status
Elamipretide is FDA approved under the brand name Forzinity.
The approval applies specifically to improving muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg.
The approval was granted through the accelerated-approval pathway.
Continued approval may depend on confirmation of clinical benefit in the required post-marketing trial.
Uses involving:
anti-aging, general fatigue, exercise performance, heart failure, kidney disease, neurological conditions, or general mitochondrial optimization
remain investigational.
It is also important to distinguish FDA-approved Forzinity from products marketed online as “SS-31.”
An unapproved research vial is not automatically equivalent to the pharmaceutical product used in clinical development.
Your Pep Resource Takeaway
SS-31 is one of the most scientifically important peptides in the library.
Its target is not appetite, hormones, or a traditional cell-surface receptor.
Its target is one of the most fundamental pieces of cellular biology:
the mitochondrial membrane.
By binding cardiolipin, elamipretide is designed to improve the environment in which the electron transport chain produces cellular energy.
That idea progressed from laboratory research to human trials and ultimately to FDA accelerated approval.
Forzinity’s 2025 approval is especially significant because it represents the first disease-specific treatment for Barth syndrome and a major proof of concept for mitochondria-targeted medicine.
The broader claims surrounding SS-31—anti-aging, generalized energy improvement, cardiovascular optimization, and neurological protection—still require considerably more evidence.
But the core science is no longer theoretical.
Elamipretide became a real FDA-approved mitochondrial medicine.
For researchers interested in mitochondria, cellular energy, cardiolipin, ATP, oxidative stress, muscle function, mitochondrial disease, cardiovascular biology, fatigue, and healthy aging, SS-31 is one of the most consequential peptides currently in the field.
Research Areas / Search Keywords
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Educational Disclaimer
This profile is provided for educational and research-information purposes only. Elamipretide is FDA approved as Forzinity specifically to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. The approval was granted under the accelerated-approval pathway and continued approval may depend on confirmation of clinical benefit in ongoing research. Discussion of aging, fatigue, cardiovascular disease, neurological disease, kidney disease, athletic performance, or other mitochondrial applications refers to experimental research and does not represent FDA-approved uses. Products marketed as research-grade “SS-31” should not be assumed to be equivalent in identity, purity, formulation, or quality to FDA-approved Forzinity.