The answer so far
Elamipretide, also called SS-31, has been studied in several different groups. An early small study found encouraging fatigue signals, but a larger study in a mitochondrial muscle disease did not meet its main walking or fatigue outcomes. Its specific US approval for Barth syndrome does not establish that SS-31 improves everyday energy or ageing in healthy people.126
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What does “energy” mean in these studies?
It can mean several things: a cell’s capacity to make ATP, a molecule used to transfer energy; a person’s reported fatigue; or what someone can do, such as walking. These measures are related but not interchangeable. A change in a hand-muscle laboratory measurement does not automatically mean that someone feels less tired or can do more in daily life. For the peptide and its approved medicine, start with the elamipretide overview.4
What did the first fatigue study find?
MMPOWER-2 enrolled 30 adults with genetically confirmed primary mitochondrial myopathy, a group of inherited conditions that can affect muscles and energy use. In this crossover study, participants received elamipretide and placebo in separate four-week periods. The main walking-distance result was not statistically significant: the estimated difference was 19.8 metres, with uncertainty ranging from 2.8 metres less to 42.5 metres more. Several secondary fatigue scores favoured elamipretide. Those encouraging patient reports were a reason for further study, not proof that all causes of tiredness respond.1
What happened in the larger study?
MMPOWER-3 randomly assigned 218 adults with primary mitochondrial myopathy to elamipretide or placebo for 24 weeks. Neither of its two main outcomes—walking distance in six minutes and a fatigue questionnaire—showed a statistically significant benefit over placebo. The estimated average change in walking distance was 14.1 metres with elamipretide and 17.3 metres with placebo: a difference of −3.2 metres, with a 95% confidence interval from −18.7 to +12.3 metres. The range reflects uncertainty; the study did not establish a benefit on these outcomes for the overall group.2
- 30 adults: MMPOWER-2The main walking result was uncertain; several secondary fatigue scores favoured elamipretide.
- 218 adults: MMPOWER-3Neither main walking nor fatigue outcome showed a significant benefit over placebo.
- 39 older adultsA single-infusion study measured hand-muscle ATP capacity and fatigue resistance.
- Barth syndromeA separate rare-disease approval uses a muscle-strength measure; confirmation is required.
Could some genetic subgroups respond differently?
Possibly, but that requires more study. Researchers examined participants with different genetic causes and saw patterns worth investigating. Some later analyses were conducted after the main trial results were known; such subgroup analyses can suggest a better-designed follow-up but are less conclusive than a successful trial designed to answer that precise question. They do not establish that a particular person will benefit. Both MMPOWER studies were funded by the medicine’s developer.23
What did the older-adult experiment measure?
A separate 2021 study enrolled 39 adults aged 60–85 selected for low measured mitochondrial function in a hand muscle. After a single infusion, one immediate percentage measure of the muscle’s capacity to produce ATP differed from placebo; the absolute change did not meet the usual statistical threshold. The difference was not seen at day seven, and resistance to fatigue in that muscle did not improve significantly. This was not a demonstration of better everyday energy, fitness or longer life.4
How does the Barth-syndrome approval fit?
Barth syndrome is a different, rare inherited disorder. In a small controlled crossover study, the main walking and fatigue measures did not show superiority to placebo. In a longer extension without a concurrent placebo group, knee-extensor strength increased. In 2025 the US FDA granted accelerated approval to Forzinity for improving muscle strength in eligible people with Barth syndrome weighing at least 30 kg, considering that measure reasonably likely to predict patient benefit. A controlled confirmatory study is required and, when checked on 5 November 2026, was listed as ongoing with scheduled completion in 2030. This approval does not establish a treatment for general tiredness or healthy ageing.567
What can a reader do with this distinction?
If tiredness is persistent or affecting daily life, a qualified clinician can help investigate possible causes and discuss appropriate care. The approved US product, a trial preparation and an online vial labelled SS-31 are not automatically the same product or quality. For a different mitochondrial-associated peptide, compare MOTS-c and its research. To explore the question beyond peptides, visit energy and tiredness.64
Sources, kept close.
Selected supporting sources; this is not a complete literature review.
- A randomized crossover trial of elamipretide in adults with primary mitochondrial myopathy (MMPOWER-2)Journal of Cachexia, Sarcopenia and Muscle / PubMed Central · Sponsor-funded primary randomized crossover trial
- Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical TrialNeurology / PubMed Central · Sponsor-funded phase 3 randomized clinical trial, 2023
- Genotype-specific effects of elamipretide in patients with primary mitochondrial myopathy: a post hoc analysis of the MMPOWER-3 trialOrphanet Journal of Rare Diseases / PubMed · Secondary and post-hoc trial analyses
- In vivo mitochondrial ATP production is improved in older adult skeletal muscle after a single dose of elamipretide in a randomized trialPLOS ONE · Randomized clinical trial, 2021
- A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndromeGenetics in Medicine / PubMed Central · Sponsor-funded clinical study, 2020
- FDA Grants Accelerated Approval to First Treatment for Barth SyndromeU.S. Food and Drug Administration · US regulatory approval announcement, 2025
- Ongoing accelerated approvals and postmarketing requirementsU.S. Food and Drug Administration · US regulator status and postmarketing requirements