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

Elamipretide, also called SS‑31, is sold to consumers as a mitochondrial peptide on the strength of laboratory findings. 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 — they measure what a person can do and how they feel, not a marker in blood.

What the trial does and does not settle

It is worth being precise in both directions here, because the temptation is to over-read a negative result as readily as a positive one.

• 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 — none of which it studied, and all of which the compound is marketed for.
• That gap is not a defense of the marketing. It is the opposite: the one population where mitochondrial function is measurably impaired, and the drug was given its best chance, is where it failed.
• A mechanism that works in cells is a hypothesis. This is what happens when the hypothesis is tested properly in people.

If a compound cannot improve exercise capacity in people whose mitochondria are demonstrably broken, the case for taking it because you are tired is not a scientific one.

Elamipretide is not an approved medicine and is sold as a research chemical. That places it outside any manufacturing standard applying to prescription drugs — a separate problem from whether it works. Our page on what FDA actually said about BPC-157 covers the regulatory position for research-use peptides generally, and /peptides carries the profiles we do maintain.