SS-31

SS-31 (also known as elamipretide in some literature) is a mitochondria- targeted tetrapeptide studied for potential protective effects in conditions characterized by mitochondrial dysfunction.

SS-31 is designed to localize to the inner mitochondrial membrane and interact with cardiolipin, with the goal of stabilizing mitochondrial structure and improving bioenergetics under stress.

Clinical programs have explored SS-31 in cardiomyopathies, mitochondrial myopathies, and other disorders, but approved uses, if any, are product- and region-specific.

Outside formal trials and labeled indications, use should be considered experimental.

Reported adverse effects vary by study and indication; up-to-date product labeling and trial reports are the primary reference for detailed safety information.

SS-31 (Elamipretide) targets the mitochondrial membrane.

This information is derived from clinical trials for mitochondrial myopathy.

Two very different formulations share this molecule. The approved product, Forzinity, is a 280 mg/3.5 mL (80 mg/mL) sterile solution for subcutaneous injection, stored at 2–8 °C, discarded eight days after first opening, and containing benzyl alcohol as an excipient — the basis of its neonate contraindication (Forzinity prescribing information, DailyMed). Research-grade "SS-31" is typically a lyophilized powder with no verified potency, sterility, or excipient disclosure.

Research includes preclinical models and human trials evaluating functional endpoints and quality-of-life measures. Results are mixed and indication- specific.

For deeper dives on this peptide, see:

• SS-31 benefits and areas of interest
• SS-31 side effects and safety context
• SS-31 dosing concepts (educational)
• SS-31 research and evidence overview

Is SS-31 FDA-approved? Elamipretide is — narrowly. It holds FDA accelerated approval as Forzinity, indicated to improve muscle strength in adult and paediatric patients with Barth syndrome weighing at least 30 kg, granted on the basis of improved knee extensor muscle strength as an intermediate clinical endpoint (Forzinity prescribing information, DailyMed). Research-grade "SS-31" is not that product and is not approved for anything.

If it was approved, why do people say it failed? Because both are true. MMPOWER-3, the pivotal phase 3 in primary mitochondrial myopathy, randomized 218 participants to 40 mg/day subcutaneous elamipretide or placebo for 24 weeks and missed both co-primary endpoints — six-minute walk distance and total fatigue score — rated Class I evidence that it does not improve those outcomes (Karaa et al., Neurology, 2023). It was approved for a different, much rarer disease where the molecular target is precisely matched.

What evidence supported the approval? TAZPOWER's 168-week open-label extension: ten patients entered on 40 mg subcutaneous daily, eight reached week 168, with a cumulative 96.1 m six-minute-walk improvement (P=0.003) and fatigue scores below baseline throughout (Thompson et al., Genetics in Medicine, 2024). Eight patients with no placebo comparator is weak evidence by ordinary standards — which is the trade-off accelerated approval is designed to make in an ultra-rare disease.

Has it worked for heart failure or macular degeneration? No approval has followed from either. PROGRESS-HF randomized 71 patients with reduced ejection fraction to placebo, 4 mg, or 40 mg daily for 28 days and did not improve left ventricular end-systolic volume (PMID 32068002); the ReCLAIM studies in dry AMD were phase 1 with safety as the primary endpoint (PMID 36246187).

What are the known side effects? The label names benzyl alcohol toxicity (contraindicated in neonates), serious hypersensitivity reactions, and eosinophilia. Injection-site reactions occurred in 12 of 12 (100%) treated patients versus 8 of 12 (67%) on placebo in the pivotal trial, with erythema at 100% versus 25%.