SS-31 and MOTS-c both act on mitochondria — the compartments inside your cells that turn food and oxygen into usable energy — and that is roughly where the resemblance ends. SS-31 sticks to a particular fat in the mitochondrial wall and helps the energy machinery hold its shape. MOTS-c is a tiny peptide your own mitochondria make, and it behaves more like a message: it flips the switch a cell uses when fuel runs low.
Different targets. Different amounts of evidence. Different reasons a doctor might reach for one rather than the other.
And on the question most people arrive with — no published clinical trial has ever given people both at the same time. Not one. Anything you have read describing a combined schedule is somebody's opinion typed up to look like a protocol.
What SS-31 and MOTS-c each actually do
SS-31, also called elamipretide, binds cardiolipin. Cardiolipin is a fat that lines the inner wall of the mitochondrion and holds the energy-producing machinery in position — think of the mortar between bricks. When that fat is damaged or built wrong, the machinery sits crooked and leaks. SS-31 attaches to it and helps the assemblies pack together properly. It is not adding fuel. It is tidying the shelf. Our guide to how SS-31 works goes deeper into the chemistry than this piece needs to.
MOTS-c is the stranger of the two. Almost every peptide in your body is built from instructions kept in the cell nucleus. MOTS-c is read out of mitochondrial DNA itself — sixteen amino acids, written in the mitochondrion's own small genome. Once released, it switches on AMPK, the cell's low-fuel alarm, the same sensor that exercise and going without food flip.
In mice fed a rich diet, MOTS-c blunted weight gain and insulin resistance (Lee et al., Cell Metabolism 2015). A later paper found that exercise raises MOTS-c in human muscle and blood, and that giving it to old mice improved how far and how well they moved (Reynolds et al., Nature Communications 2021).
One is structural. One is a signal. That distinction does most of the work in this comparison.
The human evidence, side by side
This is where the two part company sharply.
| SS-31 (elamipretide) | MOTS-c | |
|---|---|---|
| What it acts on | Cardiolipin, a fat in the mitochondrial membrane | AMPK, the cell's low-fuel switch |
| Largest completed human trial | 218 adults, 24 weeks | None reported |
| Approved product in the US | Yes, for one rare inherited disease | None, ever |
| Where the evidence is thinnest | Healthy people, long-term use | People, generally |
SS-31 has been through real trials, and the results have been mixed. In Barth syndrome — a rare inherited condition in which cardiolipin is made wrong — a twelve-person crossover study called TAZPOWER missed both of its main goals during the blinded stage; in the open-label continuation, walking distance improved by about 96 metres at 36 weeks (Thompson et al., Genetics in Medicine 2021). In a far larger trial of 218 adults with a different mitochondrial muscle disease, 24 weeks of daily SS-31 did not beat placebo on either main measure (Karaa et al., Neurology 2023).
Closest to what most people are actually curious about: 39 healthy adults aged 60 to 85 received a single infusion. Their muscles made measurably more energy than placebo that day, the effect was gone a week later, and they were no better at resisting fatigue (Roshanravan et al., PLOS ONE 2021).
MOTS-c's story is much shorter, because nearly all of it is still in animals and cells. The first randomised, placebo-controlled trial of MOTS-c itself began in February 2026 in 120 adults with prediabetes, and it has not reported. Our page on what MOTS-c research has actually tested walks through that record.
A 2026 review in Sports Medicine looked at the peptides now marketed straight to patients — MOTS-c and SS-31 among them — and landed on a blunt summary: the mechanisms are plausible and the animal work is real, but careful human safety data are scarce (Mendias and Awan, Sports Medicine 2026).
Where the regulatory line sits
On September 19, 2025 the FDA granted accelerated approval to elamipretide, sold as Forzinity, to improve muscle strength in adults and children with Barth syndrome who weigh at least 30 kg. Forzinity is FDA-approved; compounded SS-31 is not. That clearance rests on knee-extensor strength — a stand-in measurement rather than a survival or symptom result — and the label says continued clearance may depend on a confirmatory trial.
As of September 6, 2026, the day this article was written, that confirmatory trial is running. Stealth BioTherapeutics began enrolling a study called 4TAZPower on July 2, 2026: 72 weeks, randomised and placebo-controlled, 48 people with genetically confirmed Barth syndrome, built specifically to check whether the knee-extensor finding holds (NCT07531251).
MOTS-c has never had an approved product in the United States, and the compounded formulation offered here is not FDA-approved either.
None of that settles anything for one person. A licensed provider may still prescribe a compounded formulation of either compound — that decision is between you and your doctor.
Has anyone studied them together?
Nobody has, and it is worth being precise about what that absence means. A search of the public clinical-trials registry returns no interventional study listing both compounds. There is no combined dosing data, no combined safety data, and no published account of what happens to one when the other is present.
The two mechanisms do not obviously collide — one steadies a membrane, the other flips a metabolic switch. But "does not obviously collide" is reasoning, not a finding, and stacking is exactly the situation where two individually quiet compounds can turn out to be noisy together.
MOTS-c is also still being redefined. As of September 6, 2026, the day this article was written, the newest primary paper on it is not about energy at all. A study published on August 18, 2026 described MOTS-c as a host-defence peptide — a molecule with direct antibacterial activity that reprogrammes immune cells (Rice et al., eLife 2026). That is a very different job description from the metabolic one, and a fair sign that the full picture is not in yet.
How a provider chooses between them
In practice the choice is rarely "both".
What you are actually asking for. Recovery from a specific injury, a metabolic goal, and plain everyday tiredness are three different requests. They point at different compounds, or at something outside this category altogether.
Whether any evidence touches your situation. SS-31's strongest results sit inside a rare genetic disease. MOTS-c's sit in mice. Naming that gap honestly is part of the conversation, not a reason to skip it.
One change at a time. Starting two new injectables in the same week makes the outcome unreadable. If something improves, you cannot say which did it. If something goes wrong, you cannot say which caused it.
What rules it out. A provider reviews your history, your current medications, pregnancy, and anything that makes a mitochondria-targeted compound a poor idea for you specifically.
Both are prescription-only. A licensed provider reads every request and decides whether it is appropriate — not everyone qualifies, and a provider can decline. Neighbouring options sit on the energy and focus page, and the dosing questions each compound raises are covered on the SS-31 dosage page.