# Elamipretide (SS-31): The Phase 3 Trial That Missed Both Endpoints

By Nora Bissett, Pricing Editor (https://glpwatchdog.org/authors/nora-bissett) | Published: 2026-08-21 | Updated: 2026-10-30

Canonical page: https://glpwatchdog.org/research/elamipretide-a-phase-3-that-missed

> Elamipretide has what almost no research-use peptide has: a completed pivotal phase 3 trial in 218 people. It missed both primary endpoints, with a six-minute walk difference of -3.2 meters and a p value of 0.69.

## Key points

- MMPOWER-3: phase 3, randomized, double-blind, placebo-controlled, 218 participants, 24 weeks at 40 mg/day.
- Neither primary endpoint (six-minute walk distance or total fatigue) was met.
- Walk distance differed by -3.2 m (95% CI -18.7 to 12.3), p = 0.69: a result centered on nothing.
- The trial studied inherited mitochondrial myopathy, the population where the drug had its best chance, not weight loss or aging.

Elamipretide, also called SS-31, is sold to consumers as a mitochondrial peptide on the strength of laboratory findings, as is [MOTS-c](https://glpwatchdog.org/research/mots-c-what-the-evidence-shows). It has something almost no research-use peptide has: a completed pivotal phase 3 trial, randomized, double-blind and placebo-controlled, in 218 people. **It missed both of its primary endpoints.** The difference in six-minute walk distance was −3.2 meters, on the placebo side of zero, with a p value of 0.69.[1]

## What MMPOWER-3 tested

The trial enrolled people with genetically confirmed primary mitochondrial myopathy, a group of inherited disorders that impair mitochondrial energy production and reduce exercise capacity. Participants were randomized one-to-one to 24 weeks of subcutaneous elamipretide at 40 mg/day or placebo. 109 received the drug and 109 the placebo; mean age was 45.6, and 74% had mitochondrial DNA alterations.[1]

The two primary endpoints were distance walked on the six-minute walk test and total fatigue on a symptom assessment built for this condition. Both are the right kind of endpoint, because they measure what a person can do and how they feel, not a marker in blood.

*MMPOWER-3, baseline to week 24. Neither primary endpoint was met.[1]*

|   | Result |
| --- | --- |
| Randomized | 218 (109 elamipretide, 109 placebo) |
| Baseline six-minute walk | 336.7 ± 81.2 m |
| **Six-minute walk, drug vs placebo** | **−3.2 m** (95% CI −18.7 to 12.3), p = 0.69 |
| Total fatigue score | Primary endpoint not met |

> A confidence interval running from −18.7 to 12.3 meters is not a near miss or an underpowered hint. It is a result centered on nothing, in a trial large enough and long enough to have found a real effect on walking distance if one existed at this dose over 24 weeks.

## What the trial does and does not settle

A negative result can be over-read as readily as a positive one, so precision matters in both directions.

- **What it settles:** in genetically confirmed primary mitochondrial myopathy, 40 mg/day of elamipretide for 24 weeks did not improve walking distance or fatigue against placebo.
- **What it does not settle:** the trial says nothing directly about weight loss, aging, athletic recovery or general fatigue. It studied none of them, and the compound is marketed for all of them.
- That gap does not help the marketing. Primary mitochondrial myopathy is a population where mitochondrial function is measurably impaired and the drug was given its best chance, and that is where it failed.
- A mechanism that works in cells is a hypothesis, and MMPOWER-3 tested that hypothesis properly in people.

> In 218 people with primary mitochondrial myopathy, the six-minute walk result was −3.2 meters, on the placebo side of zero.

Elamipretide does have one FDA approval, and it is narrow. As Forzinity, it received accelerated approval in 2025 to improve muscle strength in adults and children with Barth syndrome (a rare inherited disorder) who weigh at least 30 kg. That approval rests on knee muscle strength, an intermediate endpoint, and continued approval may depend on a confirmatory trial.[2] It is not approved for weight loss, fatigue, aging or primary mitochondrial myopathy. The SS-31 sold to consumers for those uses is a research chemical, outside any manufacturing standard applying to prescription drugs, which is a separate problem from whether it works. Our page on [what FDA actually said about BPC-157](https://glpwatchdog.org/research/bpc-157-what-fda-actually-said) covers the regulatory position for research-use peptides generally, and our [SS-31 profile](https://glpwatchdog.org/peptides/ss-31) sets out the Forzinity label and the compounding record.

## Frequently asked questions

### Does elamipretide work?

In the one pivotal phase 3 trial, no. MMPOWER-3 randomized 218 people with genetically confirmed primary mitochondrial myopathy to elamipretide 40 mg/day or placebo for 24 weeks, and the trial did not meet either of its primary endpoints. Six-minute walk distance differed by −3.2 meters, favoring placebo, with a p value of 0.69.

### What is SS-31?

SS-31 is another name for elamipretide, a peptide that concentrates in the inner mitochondrial membrane. Its proposed mechanism concerns mitochondrial energy production, which is why it is marketed for fatigue and aging.

### Was it tested for weight loss or aging?

No. MMPOWER-3 studied primary mitochondrial myopathy, an inherited disorder. The trial says nothing directly about weight, aging or athletic recovery. It is notable, though, that the drug failed in a population where mitochondrial impairment is clearly established.

### Is elamipretide approved?

Only for one narrow use. Under the brand name Forzinity, elamipretide received FDA accelerated approval in 2025 to improve muscle strength in people with Barth syndrome (a rare inherited disorder) who weigh at least 30 kg. It is not approved for weight loss, aging, fatigue or primary mitochondrial myopathy. The SS-31 sold to consumers is a research chemical, which places it outside the manufacturing and labeling standards that apply to prescription drugs.

## References

1. Karaa A, Bertini E, Carelli V, et al. Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. Neurology. 2023. PMID: 37268435. https://pubmed.ncbi.nlm.nih.gov/37268435/
2. Stealth BioTherapeutics Inc. FORZINITY (elamipretide) injection — US Prescribing Information, Section 1 Indications and Usage (Initial U.S. Approval: 2025; accelerated approval for Barth syndrome; revised 12/2025). DailyMed (FDA-approved labeling). 2025. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=146bf34c-76f2-48db-ac07-fb29cce2cd75

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Cite as: GLP Watchdog, Nora Bissett, "Elamipretide (SS-31): The Phase 3 Trial That Missed Both Endpoints", published 2026-08-21, updated 2026-10-30. https://glpwatchdog.org/research/elamipretide-a-phase-3-that-missed

Canonical HTML page: https://glpwatchdog.org/research/elamipretide-a-phase-3-that-missed

Medical disclaimer: Nothing here is medical advice. We report on this subject; we do not treat anyone. Whether to begin a medication, supplement, or treatment, whether to adjust it, and whether to stop are questions for a clinician licensed to answer them, who knows your history.