SS-31 (Elamipretide)

What is SS-31 (elamipretide)?

SS-31 (elamipretide) is a synthetic four amino acid peptide (a tetrapeptide) that targets the inner mitochondrial membrane and binds cardiolipin (Birk et al., 2013).

Earlier research also referenced the same molecule as MTP-131 or Bendavia. Its structure is unusual for a peptide: it carries an alternating charge pattern that lets it reach the inner mitochondrial membrane on its own, without needing a receptor to carry it there. Once in place, research describes it binding cardiolipin with high affinity, a lipid found almost only in that inner membrane (Birk et al., 2013). That single feature, a small peptide that homes to the inner membrane and sticks to cardiolipin, is the reason SS-31 gets discussed as a mitochondrial compound rather than a broad metabolic one.

How does SS-31 work inside the mitochondria?

SS-31 is proposed to settle in the inner mitochondrial membrane and bind cardiolipin, the signature lipid that helps hold cristae in shape and keep the electron transport chain organized (Szeto, 2014; Birk et al., 2013).

Mitochondria make most of a cell's energy. Inside them, the inner membrane folds into structures called cristae, and those folds hold the protein complexes of the electron transport chain (ETC), the machinery that produces ATP. Cardiolipin plays a structural role in cristae formation and in organizing the respiratory complexes into supercomplexes for oxidative phosphorylation (Szeto, 2014). When cardiolipin is peroxidized or depleted, cristae curvature can be lost, respiratory supercomplexes are disrupted, and more reactive oxygen species (unstable molecules that stress the cell) leak out (Szeto, 2014).

The idea behind SS-31's development is that a peptide which binds and protects cardiolipin could help preserve cristae shape and ETC function in cells where that scaffolding is failing. In a rat ischemia model, pretreatment with SS-31 protected cristae membranes and prevented mitochondrial swelling, and the SS-31/cardiolipin complex reduced the cytochrome c peroxidase activity that drives cardiolipin peroxidation (Birk et al., 2013). Barth syndrome, the disorder elamipretide is approved to address, is exactly this kind of problem: it involves faulty cardiolipin remodeling. A cardiolipin-binding peptide aimed at a cardiolipin disorder is the through line that connects the mechanism to that program. It is worth noting that much of this mechanistic detail comes from preclinical and animal work, so it describes the proposed model rather than proven clinical outcomes (Birk et al., 2013; Szeto, 2014).

Is SS-31 (elamipretide) FDA-approved?

Yes, for one narrow use. On September 19, 2025, the FDA granted accelerated approval to elamipretide as Forzinity, marking the first approved drug for Barth syndrome, with an indication to improve muscle strength in adult and pediatric patients weighing at least 30 kg (FDA, 2025; Stealth BioTherapeutics, 2025).

Barth syndrome is a rare, inherited disorder tied to defective cardiolipin, affecting the heart and skeletal muscle. It had historically had no drug cleared specifically for it, which is why a dedicated approval is notable for the condition (Stealth BioTherapeutics, 2025). The approval was based on the TAZPOWER trial and rests on an intermediate endpoint (improved knee extensor muscle strength); as an accelerated approval, continued approval may depend on a confirmatory trial (FDA, 2025; Stealth BioTherapeutics, 2025). Elamipretide has been investigated in several other conditions over the years, but those uses are not approved, and human results outside Barth syndrome are limited. For anything beyond the approved indication, SS-31 should be treated as investigational.

What doses of SS-31 has research reported?

There is no PL dose to give here: elamipretide's personal dosing would be set by the approved product information and a prescribing clinician, not by a storefront.

The clinical program used a subcutaneous injection, delivered under the skin rather than swallowed (FDA, 2025). The specific amount, timing, and schedule for the approved Barth syndrome use are described in the product information and directed by the clinician who prescribes it. PL does not publish a milligram figure or a schedule, and nothing on this page is dosing guidance. Outside the approved indication, there is no established human dose for SS-31, so anyone weighing it should route the question to a qualified clinician.

One distinction worth stating plainly: prescription elamipretide is a medicine handled through a clinician, while research-grade SS-31 is a laboratory compound intended for research and not a product for personal use.

What is the half-life of SS-31?

We do not state a single half-life number for elamipretide, because our verified sources do not give one we can stand behind here, and its pharmacokinetics are described in the approved product information (FDA, 2025).

What we can say clearly: elamipretide is used as an injection given under the skin in its clinical program rather than as a long-acting depot, and a clinician can explain what its clearance means for a given regimen (FDA, 2025). For exact pharmacokinetic values, the product information and a clinician are the right sources. If you find a precise half-life quoted elsewhere without a citation, treat it with caution.

What side effects has SS-31 research reported?

In the Barth syndrome program, the most common adverse reactions reported for subcutaneous elamipretide were injection site reactions, such as redness, itching, or swelling, which the label notes can be managed with oral antihistamines or topical corticosteroids (FDA, 2025; Stealth BioTherapeutics, 2025).

Because SS-31 is given under the skin, local skin reactions are the effects that show up most in its clinical program (Stealth BioTherapeutics, 2025). Safety in uses beyond Barth syndrome, and in healthy people using it for other reasons, is not established, so the effects seen in a single rare-disease program should not be read as a full picture for everyone. Anyone considering elamipretide should review the approved product information and speak with a clinician, who can weigh personal risks and any interactions.

How does SS-31 compare with MOTS-c and other mitochondrial peptides?

SS-31 and MOTS-c both act on mitochondria, but through different routes: SS-31 binds cardiolipin in the inner membrane, while MOTS-c is a mitochondrial-derived peptide that switches on AMPK, a master sensor of cellular energy (Birk et al., 2013; Lee et al., 2015).

The short version: SS-31 works at the structural level of the inner membrane, aiming to keep the ETC well organized, while MOTS-c works at the signaling level, adjusting the cell's energy-management pathways (Szeto, 2014; Lee et al., 2015). They are studied for different reasons and sit at very different stages of evidence. You can read more in our MOTS-c overview, and because mitochondrial energy output is tied to how tissues repair, SS-31 also comes up in broader discussions of peptides studied for recovery. For background on peptide basics, see what are peptides.