Safety and Regulation of Peptide Use in Sports

Where MOTS-c and SS-31 stand in sport

An earlier version of this page said both peptides were banned under WADA's S0 class. That's wrong for both of them. As of October 2026, WADA's 2026 Prohibited List names MOTS-c under S4.4.1, as an activator of AMPK (a cell's energy-sensing enzyme). It is prohibited both in and out of competition. S4.4 substances are non-Specified, and USADA notes that a first violation involving a non-Specified substance carries a default four-year ban.

SS-31 (elamipretide) is a different case. On September 19, 2025, the FDA approved it as Forzinity, a prescription medicine for Barth syndrome. S0 only covers substances with "no current approval by any governmental regulatory health authority for human therapeutic use," so the approval appears to take SS-31 out of S0. The list doesn't name it anywhere else, and as of October 2026 its exact status is unverified. Our page on MOTS-c and SS-31 in tested sport covers the list wording and testing in detail.

The rest of this page is about safety: what the human data show for each molecule, and what the gray-market supply adds on top.

SS-31: human safety data from the Forzinity program

SS-31 is the only mitochondrial peptide on this site whose human safety data a regulator has reviewed. The core of it is small. The Forzinity label describes 12 males with Barth syndrome, aged 12 to 35, who received 40 mg by subcutaneous injection once a day. They first took part in a 28-week placebo-controlled crossover trial, with 12 weeks on each arm and a washout in between. Ten continued into an open-label extension. Eight stayed on the drug for 168 weeks, and three of those reached 192 weeks.

Injection-site reactions were the main finding. The label and FDA's Drug Trials Snapshot give these figures for the controlled phase:

The label also warns about hypersensitivity. Serious allergic reactions needing emergency care have been reported. Symptoms included skin rashes and cough. They can start minutes to months after treatment begins. Eosinophils, a type of white blood cell, often rose in people treated for 30 days or more. Counts peaked around 90 days and weren't linked to symptoms. The label halves the dose in severe kidney impairment and warns that its benzyl alcohol preservative is dangerous for newborns.

A larger trial in another disease points the same way. In ReCLAIM-2, a 48-week Phase 2 trial of 40 mg daily in 176 older adults with dry macular degeneration, 86% of people on elamipretide reported an adverse event, against 71% on placebo. Most were injection-site reactions.

Two limits matter for athletes. None of these trials enrolled healthy, trained people. And the data describe a pharmaceutical product made under FDA oversight. A research-use vial labeled SS-31 doesn't inherit that record, because nobody has confirmed it holds the same thing at the same strength. For what the trials say about longer use, see our page on long-term health implications of mitochondrial peptides.

MOTS-c: no human safety data yet

MOTS-c has no comparable record. The 2015 Cell Metabolism paper that described it used cells and mice, as has most research since. As of October 2026, no peer-reviewed study has given native MOTS-c to people. USADA's athlete guidance says it is unknown under what conditions, if any, MOTS-c is safe to use, because no human trial has been completed.

The nearest human data come from CB4211, a modified analog developed by CohBar. After a one-week dose-ranging stage in 65 healthy adults, 20 adults with obesity and fatty liver received either 25 mg of CB4211 or placebo by daily subcutaneous injection for four weeks. CohBar reported no serious adverse events; the only ones in more than 10% of people on CB4211 were transient injection-site reactions. Its own risk disclosures still listed a possible "inability to mitigate the prevalence and/or persistence of the injection site reactions." By 2023 CohBar said the trial formulation wasn't suitable for further development, and its planned merger was expected to end the program. CB4211 isn't the same molecule as MOTS-c, either.

User reports fill the gap, with the usual caveats. USADA lists side effects described by people who say they bought MOTS-c online. Palpitations and insomnia are on that list. So are fever and immune reactions at the injection site or across the body. None of this has been compared with placebo or separated from whatever else was in the vial. The MOTS-c overview covers the mouse evidence behind the interest.

Product quality in the research-peptide market

For both peptides, the vial may carry more risk than the molecule. Research-use products aren't made under FDA drug manufacturing rules, and no regulator tests batches before they're sold.

The largest independent dataset so far comes from a preprint (not yet peer-reviewed) posted in April 2026 by Christopher Mendias and Tariq Awan, who analyzed 6,441 test reports from Finnrick Analytics, a public third-party testing platform, covering 14 peptides from 203 synthesis companies. Depending on how strict a standard they applied, 41.6% to 71.1% of samples failed basic purity or dose criteria. Wrong dosing was the most common failure. Of the 243 samples with endotoxin results, 15% had measurable endotoxin. Endotoxins are fragments of bacterial cell walls that can cause fever and inflammation when injected. High purity didn't predict low endotoxin: some samples above 99.5% purity still had concerning levels.

That dataset didn't include MOTS-c or SS-31, and it has selection bias, since vendors choose what to submit. The authors also note that purity tests miss other problems. Published analyses of seized products have found heavy metals and leftover synthesis reagents, as well as wrong sequences and vials with no active ingredient at all. Health Canada's April 2026 advisory, which lists both MOTS-c and SS-31 among seized peptides, warns that such products may hold the wrong amount of the active ingredient or none at all. They may also be contaminated with solvents or microbes. Our page on how MOTS-c and SS-31 are made and tested explains where impurities come from and what a certificate of analysis can show.

Contamination and inadvertent doping

For a tested athlete, a mislabeled vial is also an anti-doping problem. A positive test, in USADA's definition, is a lab report that a prohibited substance is present in the sample. What the label said doesn't change that finding.

The same risk has been documented in supplements for decades. In a study of 634 non-hormonal supplements bought in 13 countries in 2000 and 2001, 94 (14.8%) contained anabolic steroids that weren't on the label. Small amounts of the nandrolone precursors found in some products produced positive urine tests for several hours. USADA still warns that some supplements are spiked with performance-enhancing drugs or research compounds, and that batches of one product can differ in what they contain.

Research-use peptides carry the same uncertainty, with an injection in place of a capsule. With MOTS-c the question is moot, since the labeled substance is already prohibited at all times. USADA says a therapeutic use exemption for it is highly unlikely, because it has no approved medical use. With SS-31, the athlete is exposed to both an unsettled list status and whatever the vial actually contains.

What "research use only" means

The "for research use only, not for human consumption" label describes how a product is sold. It isn't a safety rating, and regulators don't treat it as a legal shield. In an August 24, 2026 warning letter to Tex Peptides that named SS-31 among other products, the FDA said the research-use statements didn't change its finding: these were unapproved new drugs intended for human use. Part of its evidence was that the seller also sold bacteriostatic water for reconstituting them. Health Canada's 2026 advisory says the same labeling "does not make these products legal or exempt from regulatory requirements."

For the buyer, research-use labeling means no regulator has checked what's in the vial or how much. A vial labeled SS-31 is not Forzinity. The prescription drug is made under FDA manufacturing controls and comes with an approved label; the research vial has neither. Problems can still be reported: Health Canada's advisory asks people who used these products to report side effects.

What we still don't know

• How WADA treats SS-31 now that it is approved. As of October 2026, this is unverified.
• How SS-31 behaves in healthy, trained people, or at the much lower doses users describe. No study has tested either.
• Whether native MOTS-c is safe in people at any dose. No completed human trial exists.
• How often MOTS-c and SS-31 vials fail quality tests. The large 2026 testing dataset didn't cover either peptide.