Research guide

MOTS-c vs SS-31: two approaches to mitochondrial research

Evidence checked 17 October 2026

Mitochondria help cells process fuel and produce usable energy, but they also participate in signalling. (Lee et al., 2015) MOTS-c and SS-31 are interesting examples of two different research approaches to those functions. (Lee et al., 2015) (Mitchell et al., 2020)

MOTS-c is a 16-amino-acid peptide encoded within mitochondrial DNA, while SS-31, also called elamipretide, is a designed four-amino-acid peptide. (Lee et al., 2015) (Mitchell et al., 2020) They are different molecules, not two names for the same compound.

The short answer

MOTS-c: Research includes metabolic signalling, animal exercise performance and measurements of naturally produced MOTS-c during human exercise. (Lee et al., 2015) (Reynolds et al., 2021)
SS-31: Research focuses on mitochondrial membranes; the elamipretide medicine Forzinity has a specific US accelerated approval for Barth syndrome. (Mitchell et al., 2020) (FDA Forzinity trial snapshot)
The useful comparison: The papers here ask different questions in different models and populations, not which peptide produces better everyday energy in healthy people. (Reynolds et al., 2021) (MMPOWER-3, 2023) (FDA Forzinity trial snapshot)

At a glance

The molecule

MOTS-c: A 16-amino-acid, mitochondrial-encoded peptide. (Lee et al., 2015)
SS-31: Elamipretide, a designed tetrapeptide, meaning four amino acids. (Mitchell et al., 2020)

A major research thread

MOTS-c: Metabolic signalling, including AMPK, an energy-sensing enzyme. (Lee et al., 2015) (Gudiksen et al., 2026)
SS-31: Interactions with mitochondrial membranes and cardiolipin, a fat-like component of those membranes. (Mitchell et al., 2020) (Forzinity prescribing information)

Examples of human evidence

MOTS-c: Exercise-related measurements of natural MOTS-c levels, plus a registered metabolic-treatment study design. (Reynolds et al., 2021) (MOTS-MET trial registration)
SS-31: Interventional studies in specific mitochondrial diseases, with results that depend on the population and endpoint. (MMPOWER-3, 2023) (FDA Forzinity trial snapshot)

MOTS-c: why metabolism researchers are interested

The 2015 discovery paper linked MOTS-c with metabolic signalling and AMPK activation in laboratory experiments. (Lee et al., 2015) In mice, treatment helped prevent high-fat-diet-related obesity and insulin resistance, as well as age-related insulin resistance. (Lee et al., 2015)

Those findings helped establish a research question about how mitochondria communicate with the rest of the cell. (Lee et al., 2015) They were not a human weight-loss trial, so the mouse outcomes should not be presented as a measured human fat-loss effect.

Exercise research: mice and people answered different questions

A 2021 paper reported improved physical performance after MOTS-c treatment in young, middle-aged and older mice. (Reynolds et al., 2021) Its human component involved 10 young men exercising on stationary bicycles, with researchers measuring naturally produced MOTS-c in muscle and blood. (Reynolds et al., 2021)

That human experiment did not test whether administering MOTS-c improved performance. (Reynolds et al., 2021) A natural response to exercise and a benefit from an administered peptide are different questions.

A 2026 study added mechanistic detail, reporting improved mitochondrial efficiency in mouse muscle and investigating MOTS-c measurements around exercising human muscle. (Gudiksen et al., 2026) It did not turn those human measurements into a treatment trial. (Gudiksen et al., 2026)

Human MOTS-c treatment research: a registration is not a result

The MOTS-MET registry listing describes a randomised, placebo-controlled phase 2 study of MOTS-c in adults with prediabetes and overweight or obesity. (MOTS-MET trial registration) The listed question is whether treatment improves insulin sensitivity and related metabolic measures. (MOTS-MET trial registration)

That is a useful next-stage research question. A registered study design is not an efficacy finding, and it should not be quoted as proof that the treatment works.

SS-31: a membrane-focused approach

SS-31 research examines its interaction with mitochondrial membranes, including membranes containing cardiolipin. (Mitchell et al., 2020) A 2020 study used model membranes, mitochondrial membranes and computer-based analysis to examine changes in membrane properties. (Mitchell et al., 2020)

The Forzinity label identifies elamipretide as a mitochondrial cardiolipin binder that localises to the inner mitochondrial membrane. (Forzinity prescribing information) That gives it a different mechanistic focus from the metabolic-signalling work discussed for MOTS-c.

A clinical milestone with a specific population

On 19 September 2025, the FDA granted accelerated approval to Forzinity to improve muscle strength in adults and children with Barth syndrome weighing at least 30 kg. (FDA Forzinity trial snapshot) Barth syndrome is a rare inherited condition that can weaken the heart and muscles used for movement. (MedlinePlus: Barth syndrome) This is a specific US medicine indication, not approval for general fatigue, exercise enhancement or anti-ageing.

The supporting programme enrolled 12 patients in a randomised crossover study followed by an open-label extension, where participants and researchers knew the treatment being used. (FDA Forzinity trial snapshot) The initial randomised portion did not show superiority to placebo on the walking-distance and fatigue primary endpoints; knee-muscle-strength improvements were observed during the longer open-label period. (FDA Forzinity trial snapshot)

Accelerated approval was based on that muscle-strength finding, with confirmatory evidence required to verify clinical benefit. (Forzinity prescribing information) Keeping the approval and the study design together gives a more accurate picture of the milestone.

Why one mitochondrial condition is not every condition

MMPOWER-3, published in 2023, randomised 218 people with primary mitochondrial myopathy, a genetic mitochondrial muscle condition, to elamipretide or placebo for 24 weeks. (MMPOWER-3, 2023) It did not meet its primary walking-distance or fatigue endpoints, although most adverse events were described as mild to moderate. (MMPOWER-3, 2023)

That was a different patient group from the Barth syndrome programme. (MMPOWER-3, 2023) (FDA Forzinity trial snapshot) It shows why a result for a particular condition cannot be applied automatically to every mitochondrial disorder or to healthy adults.

What newer cell research adds

A 2026 MOTS-c study examined human fat-derived cells used in tissue-repair research outside the body, then tested their reparative effects in a mouse kidney model. (Xing et al., 2026) It found AMPK activation alongside reduced cell growth, increased markers linked with cellular ageing and inflammation, and no restoration of the expected repair function. (Xing et al., 2026)

This is a finding about a specific cell-and-animal model, not a clinical outcome in people. (Xing et al., 2026) The useful lesson is that activating a metabolic signal does not automatically improve every function of a cell.

The clear takeaway

MOTS-c offers a metabolic-signalling and exercise-research story; SS-31 offers a membrane-focused story with interventional human studies and a narrowly defined US medicine approval. (Reynolds et al., 2021) (Mitchell et al., 2020) (FDA Forzinity trial snapshot) The studies here do not establish a head-to-head winner for everyday energy or longevity.

Safety belongs alongside the findings: the Forzinity label includes serious allergic-reaction warnings and common injection-site reactions. (Forzinity prescribing information) That medicine's evidence also does not establish the quality or safety of a separately supplied SS-31 product.

The TGA says relevant human evidence must match the specific peptide, formulation, route and condition, and that unapproved peptide products have not been assessed for safety, quality or effectiveness. (TGA peptide-evidence guidance) This keeps the interesting science attached to what was actually tested, rather than turning two research approaches into a recommendation to use or combine them.

This guide explains published research, not recommendations for personal use. It provides no dosing, administration or combining instructions. Findings apply to the materials, formulations and settings studied; they do not establish the safety, quality or suitability of a separately supplied research-labelled product.