SS-31 Peptide (Elamipretide): Cardiolipin Targeting, Mitochondrial Research, and Regulatory Status

The SS-31 peptide — also written SS31 and developed clinically as elamipretide — is a synthetic tetrapeptide designed to reach the inner mitochondrial membrane and bind cardiolipin, the phospholipid that holds the electron transport chain's protein complexes together. Most compounds discussed in longevity medicine act on a signaling pathway that eventually reaches the mitochondrion. SS-31 was engineered to go to the mitochondrion directly. That makes it one of the more mechanistically specific molecules in the category, and it is also one of the few that has been through a formal pharmaceutical development program. This page covers its structure, mechanism, clinical research, regulatory position, and what is and is not established about dosing.

What the SS-31 Peptide Is

The Szeto-Schiller Peptides

SS-31 belongs to a family of small aromatic-cationic peptides known as the Szeto-Schiller (SS) peptides, named for Hazel Szeto and Peter Schiller, whose laboratories described them. The family was built around an alternating pattern of aromatic and positively charged amino acids. That pattern lets the peptides cross cell membranes despite carrying a net positive charge, and it drives them toward the inner mitochondrial membrane, where they accumulate.

SS-31 is the member of the family that moved furthest into clinical development. It has appeared in the literature and in trial registries under several names — SS-31, MTP-131, Bendavia, and elamipretide — which is worth knowing when searching the research, because the same molecule is reported under different labels depending on the year and the sponsor.

Structure at a Glance

The D-arginine at the first position and the amidated C-terminus are design choices that make the peptide more resistant to enzymatic breakdown than a comparable all-L sequence would be.

How SS-31 Works: Cardiolipin and the Inner Membrane

Why Cardiolipin Matters

Cardiolipin is a phospholipid found almost exclusively in the inner mitochondrial membrane. It is not a passive structural lipid. It anchors and organizes the respiratory complexes, supports the tight folding of the membrane into cristae, and interacts with cytochrome c, the small protein that shuttles electrons between Complex III and Complex IV.

When cardiolipin is oxidized or remodeled abnormally, several things go wrong at once. Cristae architecture degrades, the respiratory complexes become less efficient, electron leak increases, and cytochrome c's behavior changes in ways associated with oxidative damage and, eventually, apoptotic signaling. Cardiolipin abnormality is a defining feature of Barth syndrome, and cardiolipin oxidation has been described in models of aging, ischemia, and heart failure.

What SS-31 Is Proposed to Do

SS-31 binds cardiolipin. Preclinical research suggests that binding:

• Stabilizes inner-membrane architecture, helping preserve cristae structure under stress.
• Supports electron transport efficiency, with less electron leak and reduced reactive oxygen species (ROS) generation at the source.
• Modulates cytochrome c's interaction with cardiolipin, limiting the peroxidase activity that drives cardiolipin oxidation.

The distinction from a conventional antioxidant is important. SS-31 is not primarily a free-radical scavenger that mops up ROS after they form. It is proposed to reduce ROS production by keeping the machinery that generates them working properly. That is a meaningful mechanistic claim, and it is supported by a substantial body of cell and animal work — but the size of the effect in humans, and in which conditions it is clinically relevant, is what the clinical program has been working out.

Research and Clinical Development

Preclinical Work

SS-31 has been studied across a wide range of animal and cell models: cardiac ischemia-reperfusion injury, heart failure, kidney injury, skeletal-muscle aging, and neurodegeneration among them. Aged-animal studies reporting improved mitochondrial function and exercise tolerance are a large part of why the peptide attracts interest in longevity medicine.

As with most peptides in this category, the preclinical literature is more consistently positive than the human data. Rodent aging studies measure mitochondrial endpoints that do not map directly onto outcomes a patient would feel or a clinician would measure.

Human Trials

Elamipretide has been evaluated in human trials across several indications. Two are especially relevant:

• Primary mitochondrial myopathy. A large phase 3 trial did not meet its primary endpoints. That result matters for anyone extrapolating from mechanism to benefit: a molecule with a well-characterized mitochondrial target still did not produce the primary functional improvement the trial was designed to detect in that population.
• Barth syndrome. A rare X-linked disorder of cardiolipin remodeling — the condition in which SS-31's mechanism is most directly relevant. In the Barth program's randomized trial (TAZPOWER), the double-blind phase did not meet its primary endpoint; the regulatory filing discussed below leaned on longer-term open-label extension data.

Smaller studies have also explored heart failure, kidney disease, and age-related eye disease. None of these has established a longevity or healthy-aging indication. There is no controlled human evidence that SS-31 slows aging in healthy adults.

Regulatory Status

In 2025, FDA granted accelerated approval to elamipretide, marketed as Forzinity, to improve muscle strength in patients with Barth syndrome weighing at least 30 kg. Accelerated approval is based on an endpoint judged reasonably likely to predict clinical benefit, and it typically carries a requirement to confirm that benefit in further study.

That approval is narrow, and it does not settle the questions most relevant to longevity practice:

• Off-label use of the approved product for other conditions is a prescriber decision made against a very limited evidence base outside the approved indication.
• Compounded SS-31 is a separate question. SS-31 does not appear on the site's FDA peptide status tracker, and we are not aware of a determination establishing it as eligible for 503A compounding from bulk. With an approved product now on the market, federal rules also restrict compounding a drug that is essentially a copy of it. 503A eligibility should be treated as not established; confirm with the compounding partner before any prescribing decision.

For how the 503A pathway works generally, see what a 503A compounding pharmacy is.

SS-31 Dosage: What Is and Is Not Established

Labeled dosing exists only for the approved product, in its approved indication. For Barth syndrome, prescribers should follow the Forzinity prescribing information.

Outside that indication, there is no established SS-31 dose. Clinical trials used defined regimens for specific populations and endpoints, but those regimens were not shown to produce benefit in healthy aging and are not validated for longevity use. Figures circulating online for "anti-aging" SS-31 protocols are not derived from controlled evidence, and they should not be treated as a dosing reference.

Any SS-31 use outside the approved indication is a prescriber-determined, off-label decision that needs a clear rationale, informed consent that reflects the thin evidence, and monitoring. If a patient is using SS-31 obtained outside a legitimate prescription channel, the first clinical concern is the unknown identity, purity, and sterility of the product.

For general reconstitution and injection technique, see how to reconstitute peptides and how to inject peptides.

Safety and Side Effects

In published trials, injection-site reactions — redness, itching, swelling, and discomfort at the injection site — were the most frequently reported adverse effects. They were generally described as mild to moderate, but they were common enough that they shaped tolerability in the longer studies.

What is not known matters as much:

• Long-term safety in healthy adults has not been studied.
• Interactions with other mitochondrially active compounds, such as methylene blue, have not been systematically characterized.
• Pregnancy and lactation lack adequate data.
• Compounded or research-grade material carries risks unrelated to the molecule itself: contamination, incorrect content, and non-sterile preparation.

SS-31 Compared With Other Mitochondrial Approaches

SS-31 is often grouped with other compounds used in mitochondrial and longevity protocols. They act at different points and carry very different evidence and regulatory profiles.

The table is a map, not a ranking. The mechanisms differ, and none of these compounds has controlled human evidence that it extends healthy lifespan. The broader picture is covered in our guide to anti-aging peptides.

Where SS-31 Fits

SS-31 is a well-characterized molecule with a precise mitochondrial target and a real clinical development history — including a failed phase 3 in one mitochondrial disease and an approval in another. That record argues for caution in both directions: the mechanism is credible, but mechanism alone has not reliably predicted clinical benefit.

For longevity practice, the honest framing is that SS-31 is investigational outside Barth syndrome, that its compounding status is unresolved, and that any use should be supervised and documented. Newtropin does not prescribe, compound, or dispense. We connect licensed providers with a licensed 503A compounding partner; prescribers can start at For Providers.

Frequently Asked Questions

What is the SS-31 peptide?

SS-31 is a synthetic aromatic-cationic tetrapeptide from the Szeto-Schiller family that concentrates in the inner mitochondrial membrane and binds cardiolipin. It has been developed clinically under the name elamipretide.

Is SS-31 the same as elamipretide?

Yes. SS-31, MTP-131, Bendavia, and elamipretide are names for the same molecule, used at different stages of research and development.

Is SS-31 FDA-approved?

Elamipretide received FDA accelerated approval in 2025 as Forzinity for Barth syndrome. That approval covers the specific product and indication. It does not establish other uses or make compounded SS-31 eligible for 503A compounding.

What is the SS-31 dosage?

Labeled dosing exists only for the approved product in Barth syndrome, per its prescribing information. There is no established dose for longevity or other off-label uses, and online protocols are not based on controlled evidence.

What are the side effects of SS-31?

Injection-site reactions were the most commonly reported adverse effects in clinical trials. Long-term safety in healthy adults has not been studied.

How is SS-31 different from MOTS-c?

SS-31 binds cardiolipin in the inner mitochondrial membrane and has been through phase 3 trials. MOTS-c is a mitochondrial-derived signaling peptide acting through AMPK, with no human effectiveness data; FDA proposed in July 2026 that it not be added to the 503A Bulks List.