SS-31 vs MOTS-c: differences, evidence and safety

Answer first

SS-31 (elamipretide) is a laboratory-built peptide that binds a fat in the mitochondrial membrane. MOTS-c is a peptide the body makes from its own mitochondrial DNA. SS-31 is approved in the United States for one rare disease, while MOTS-c is approved nowhere. No study comparing the two could be found in the sources reviewed for this page.

At a glance

How they work

Both substances point at the mitochondria, the tiny power plants inside our cells. Beyond that shared target, the molecules and their origin differ ^[1].

SS-31 is the laboratory code for elamipretide, a chain of just four amino acid building blocks ^[2]. The approved American package insert says only that it gathers in the inner membrane of the mitochondria and improves their shape and function ^[3]. The more detailed picture comes from cells and animals:

• It binds cardiolipin, the fat that gives the inner membrane its folds and holds the cell's energy machinery in place ^[4].
• Once bound, it is reported to stop a chemical attack that would otherwise damage that fat and make the folds collapse ^[4].
• Its chemical make-up is said to let it cross membranes on its own, without a carrier ^[5].
• No receptor and no hormone system are involved. The proposed effect depends on where the molecule settles.

MOTS-c is a peptide of 16 building blocks ^[6]. Its blueprint sits inside a gene of the mitochondria, not in the DNA of the cell nucleus ^[7]. Everything below comes from cells or animals:

• It is said to block a chain of reactions built around folate. A substance called AICAR then builds up and may switch on the cell's fuel gauge, the enzyme AMP-activated protein kinase (AMPK) ^[7].
• When cultured cells were starved of sugar, the peptide moved into the nucleus and settled next to genes that defend against chemical stress ^[8].
• One group reported that it binds and switches on a second enzyme in muscle, casein kinase 2 ^[9].
• Two findings point the other way. Peptides of this family made worn-out cells release more inflammatory signals ^[10], and in human connective tissue cells MOTS-c weakened repair ^[11].

The core difference: SS-31 was designed to stick to a membrane fat, while MOTS-c is the body's own signal thought to act through enzymes. Neither mechanism is confirmed in people.

What the studies show

No study that compares SS-31 and MOTS-c directly could be found in the published record reviewed for this page. The two monographs mention each other only for contrast, not as part of a shared experiment.

What follows are separate studies of each substance. They involved different species, different illnesses, different measurements and different lengths of treatment. The numbers cannot be set against each other.

SS-31: Barth syndrome, the approved use

Phase 2/3 RCT TAZPOWER enrolled twelve male patients aged twelve and over with Barth syndrome, a rare inherited disease. Each patient received the drug and a dummy treatment in turn. Neither of its two main measures improved: not the distance walked in six minutes, and not the fatigue score ^[12].

The strength of the muscle that straightens the knee rose by a middle value (median) of 4 newtons on the drug. On the dummy treatment it fell by 5 newtons ^[3].

Open-label extension In the follow-on phase, everyone knew what was being given and there was no comparison group. Against the starting point, the median gain was 34 newtons at week 12 in ten patients. It reached 68 newtons at week 24 in nine, and 63 newtons at week 168 in eight ^[3], ^[13].

Walking distance rose by 95.9 metres at week 36 and by 96.1 metres at week 168 ^[13]. A phase like this cannot separate a drug effect from the natural course of the illness or from practice at the test. That is why the regulator made a confirmatory trial a condition of approval ^[14].

SS-31: mitochondrial muscle disease, the failed trials

Phase 3 RCT MMPOWER-3 followed 218 adults with a genetically confirmed muscle disease caused by faulty mitochondria for 24 weeks. Patients on the drug walked 3.2 metres less far than those on dummy treatment. The range compatible with the data ran from 18.7 metres worse to 12.3 metres better (p = 0.69) ^[15].

Fatigue did not differ either. The authors read the result as strong evidence that elamipretide does not help with these measures ^[15].

Phase 1/2 and phase 2 RCT Two earlier trials looked more hopeful but also missed the mark. In 36 adults, the highest dose group walked 64.5 metres further against 20.4 metres on dummy treatment (p = 0.053) ^[16]. In 30 adults who received both treatments in turn, the gain over dummy treatment was 19.8 metres (p = 0.0833) ^[17].

SS-31: heart and eye trials

Phase 2a RCT EMBRACE STEMI gave the drug through a drip to 300 patients who had just had a heart attack. The amount of heart muscle destroyed came out almost identical in the two groups. Imaging and how the patients fared showed no benefit either ^[18].

Phase 2 RCT PROGRESS-HF followed 71 patients with weak heart pumping over 28 days. The blood left in the main chamber after each beat barely changed. At the two doses tested, it differed from dummy treatment by less than 3 millilitres (−0.3 and 2.3 millilitres) ^[19].

Phase 2 RCT ReCLAIM-2 followed 176 patients aged 55 and over with dry age-related macular degeneration, an eye disease, for 48 weeks. Both main questions came out negative: sight in dim light and the growth of the damaged patch of retina ^[20].

SS-31: ageing muscle

Phase 2 RCT, single dose The trial enrolled 39 adults aged 60 to 85 with poorly working mitochondria. One drip raised the maximum amount of cellular fuel their muscles could produce (p = 0.045 for the percentage change). By day seven the difference had gone. Resistance to muscle fatigue did not change ^[21].

MOTS-c: metabolism in mice

Animal data The 2015 study that first described the peptide treated two strains of mice, 6 to 8 animals per group. They cleared sugar from the blood faster and responded better to insulin. On a fattening diet they neither grew obese nor became resistant to insulin ^[7].

In mice prone to autoimmune diabetes, treatment from week 7 delayed the disease, in groups of 6 to 10 animals ^[22]. No controlled study in people repeating either result could be found in the sources reviewed.

MOTS-c: running performance in mice

Animal data In mice aged 2, 12 and 22 months, in groups of 5 to 10, treadmill running improved at every age. Animals that started treatment at 23.5 months, roughly old age for a mouse, performed better and stayed healthy for longer ^[23].

Animal data In another study, wheel running raised the animals' own MOTS-c in muscle by about 1.5- to 5-fold. In untrained mice, a single dose lengthened running time by 12 per cent and distance by 15 per cent ^[24].

MOTS-c: measurements in people

Observational These studies measured the peptide the body makes itself. Nobody was given anything. In ten young men who did not exercise regularly, hard interval training raised MOTS-c in muscle and blood ^[23].

Observational In 10 lean people and 10 people with obesity, blood levels were much the same. They measured 0.48 ± 0.16 against 0.52 ± 0.15 nanograms per millilitre (p = 0.60). The level moved loosely with two measures of insulin response, the HOMA index (r = 0.53) and the Matsuda index (r = −0.46) ^[25].

Observational In 125 participants in China and 34 women in Europe, the 26 with metabolic syndrome had more MOTS-c, not less. Their level was 315 picograms per millilitre (315 ± 27) and rose with the fat in their livers ^[26]. The authors read this as the liver signalling distress rather than as a protective effect.

MOTS-c: the unverified trial entry and the analogue

Registry entry One entry in the American trial registry claims a study of MOTS-c in adults with prediabetes. Its sponsor filed further entries that call themselves mock, example or fictional records. The entry is therefore not counted as a trial here ^[27].

Phase 1 (press release only) CB4211 is a chemically altered relative of MOTS-c, not the peptide itself. Its early-stage trial ran in 88 participants between July 2018 and April 2021 ^[28]. Its third part treated 20 participants with obesity and fatty liver disease for four weeks.

Two liver enzymes fell by 21 and 28 per cent. On placebo, one rose by 4 per cent and one fell by 11 per cent. Blood sugar fell by 6 per cent against no change, and each difference counted as more than chance (p < 0.05) ^[29].

These figures come from a company press release that was not peer-reviewed, and the registry lists no posted results ^[28], ^[29]. The company later declared the preparation unsuitable for further development ^[30].

Safety

The two safety records differ mainly in how much is known. SS-31 has an official American package insert built on a small approval data set. For MOTS-c itself, no verified trial in people and therefore no list of side effects could be found. That difference in data is not a ranking of risk.

SS-31, from the package insert and the trials ^[3]:

• Reactions where the needle goes in affected all 12 treated patients in the approval data, against 8 of 12 on dummy treatment. Redness at the site affected 12 of 12, against 3 of 12.
• Pain at the site affected 9 of 12 against 5 of 12, and hardening and itching each 8 of 12 against 2 of 12.
• Eosinophils, white blood cells involved in allergy, rise from around day 30, peak near day 90 and settle again. The package insert describes no ill effects from this.
• The only absolute bar to use is a severe allergic reaction to any ingredient. The preserved form contains benzyl alcohol, which newborn babies cannot cope with.
• In a trial in mitochondrial muscle disease, injection site reactions affected 80% of participants, mostly mildly ^[17]. In the eye trial, side effects of any kind reached 86% against 71% on dummy treatment ^[20].

Whether elamipretide can cause cancer had not been established when it was approved. The regulator required two animal studies on that risk, one reporting in 2026 and one in 2030 ^[14]. The twelve approval patients were all male and aged 12 to 35, so rare risks and effects in women or young children remain open ^[3].

MOTS-c, from regulators and the analogue trial:

• The United States Anti-Doping Agency states that the American regulator has not approved MOTS-c for use in humans ^[31].
• People who said they had bought MOTS-c online reported a faster heartbeat, palpitations, sleeplessness, immune reactions and fever. No source that could be found checked whether the substance caused this or what the products contained ^[31].
• The American regulator flagged possible immune reactions, impurities in the material and a poorly characterised substance ^[32], ^[33].
• In the four-week part of the CB4211 trial, the only complaints affecting more than one in ten participants were brief injection site reactions. No serious side effects were reported among the 88 participants ^[28], ^[29].

For the natural peptide, no published data could be found on how the body absorbs and clears it. No data in pregnancy, in children or in liver or kidney damage could be found either.

Why this page lists no doses. Elamipretide is prescription-only in the one country that has approved it and experimental everywhere else. Amounts belong in the official product information or the trial documents, and in the hands of the doctor using them. This page therefore follows the stricter rule for both substances and reports results without the amounts given.

Legal status

Elamipretide received a fast-track American approval on 19 September 2025, for Barth syndrome only ^[14]. Europe has granted it rare disease status, which is not an approval ^[34], and other registers list no authorisation ^[35]. MOTS-c is approved nowhere. Since 2023 the American regulator has classed it as a safety risk for pharmacy compounding ^[33]. No final decision followed a July 2026 advisory vote ^[32], ^[36]. MOTS-c is banned in sport at all times under section S4.4.1. SS-31 is not named, but section S0 still covers material sold under the laboratory code ^[37]. More at peptides banned in sport. Both monographs were checked on 6 September 2026.

Used together?

The peptide directory under blends lists no combination of SS-31 and MOTS-c. MOTS-c appears in one blend, MitoPrime, together with 5-Amino-1MQ and NAD+. SS-31 appears in no blend in the directory.

No study of SS-31 and MOTS-c given together could be found in the SS-31 or MOTS-c monographs or in their sources.

Frequently asked questions

Which is better, SS-31 or MOTS-c?

The studies cannot answer that, because no trial comparing the two could be found in the sources reviewed for this page. In 218 adults with a mitochondrial muscle disease, SS-31 missed its main goal over 24 weeks. For MOTS-c, the results come from mice, and no verified trial giving the peptide itself to people could be found.

Is SS-31 or MOTS-c safer?

The data give no answer, because no study comparing their safety directly could be found in the sources reviewed here. In the approval data for SS-31, all twelve treated patients had a reaction where the needle went in, against eight of twelve on dummy treatment. For MOTS-c itself, no verified list of side effects in people could be found.

What is the difference between SS-31 and MOTS-c?

SS-31 is a chain of four building blocks made in a laboratory to stick to cardiolipin, a fat in the inner mitochondrial membrane. MOTS-c has 16 building blocks, and its blueprint sits in the DNA of the mitochondria themselves. SS-31 holds one American approval, while MOTS-c is approved nowhere and is banned in sport by name.

Can SS-31 and MOTS-c be taken together?

No study of the two given together could be found in the sources behind this page. The peptide directory lists no blend that contains both. MOTS-c appears in one blend, MitoPrime, alongside 5-Amino-1MQ and NAD+, and MOTS-c itself is approved nowhere.

Are SS-31 and MOTS-c approved medicines?

SS-31, under its official name elamipretide, received a fast-track approval in the United States on 19 September 2025, for Barth syndrome only. No other country had approved it when the registers were checked on 6 September 2026. For MOTS-c, the same checks found no approval in any of the seven markets.

Are SS-31 and MOTS-c banned in sport?

MOTS-c is banned at all times and named in section S4.4.1 of the 2026 Prohibited List. SS-31 is not named on the list. Material sold under the laboratory code is not an approved medicine, so the general ban in section S0 still covers it. Athletes should ask their national anti-doping body.

Is SS-31 the same substance as elamipretide?

Yes. SS-31 is the laboratory code, and elamipretide is the official international name. Older records also use MTP-131, RX-31 and SBT-131. Powder sold under the code is not the same thing as the approved medicine, whose content and purity are checked.

Have SS-31 and MOTS-c been tested in people?

SS-31 has, in several controlled trials in hundreds of patients, most of which missed their main goals. For MOTS-c, the human studies that could be found only measure the peptide the body makes itself. In the sources reviewed, the only close relative given to people was an altered molecule called CB4211, which its maker later dropped.