SS-31 benefits and uses

The approved use: Barth syndrome

Barth syndrome is a rare, serious disease of the mitochondria that mainly affects males.² It often begins with severe heart failure in infancy, and survivors tend to have fatigue and poor stamina.² FDA reviewers estimated about 130 affected people in the United States.³

The pivotal trial, TAZPOWER, enrolled 12 males aged 12 to 35 at one U.S. site.¹¹⁰ In its randomized crossover part, elamipretide was not better than placebo for walking distance or fatigue.¹ FDA reviewers concluded that this part failed its primary objective.³

Knee extensor strength (median 124 newtons at baseline) rose only later, in the open-label extension, where every patient knew they were on the drug:¹

Walking distance improved at every extension visit, by a cumulative 96.1 m at week 168, with no placebo group for comparison.¹⁷ Against 19 untreated patients from natural-history records, 8 treated patients walked 79.7 m farther at week 64 and 91.0 m farther at week 76.¹⁸ FDA reviewers warned that effort-based tests like walking are open to bias when patients know they are treated, including in comparisons of this kind.³

FDA approved Forzinity on the strength result, which it treats as reasonably likely to predict benefit such as standing more easily or walking farther.² A confirmatory trial must still show that benefit.²

Results in other conditions

Two follow-ups matter for myopathy. A post hoc look at MMPOWER-3 found a trend in patients with mitochondrial DNA maintenance (replisome) variants, mostly POLG and TWNK.¹¹ Their walking distance rose 25.2 m, against 2.0 m on placebo (p = 0.06).¹¹ A post hoc subgroup result like this can suggest a hypothesis but cannot confirm a benefit. NuPOWER, a 48-week phase 3 trial in 102 adults, finished on December 4, 2024, and had posted no results as of October 2026.²⁴ The company says its data support work in a POLG1 subgroup.²⁵ The ReCLAIM-2 retinal measure became the main endpoint of the phase 3 ReNEW trial, with results expected in late 2027.⁸²⁶²⁷

Aging, muscle, brain and skin: mostly animal data

• Muscle in old mice: an hour after one injection, 27-month-old mice matched young mice in muscle energy output.⁵ After 8 days, their endurance rose.⁵
• Muscle over 8 weeks: aged female mice had heavier, more fatigue-resistant calf muscle and ran longer on a treadmill than untreated aged mice.⁹
• Heart in aged mice and rats: SS-31 cut excess proton leak in heart mitochondria and largely reversed age-related diastolic dysfunction (impaired relaxation).¹²
• Brain in old mice: 24-month-old mice treated for 2 weeks had better brain blood-flow responses, spatial working memory, motor learning and gait coordination.²⁸
• Muscle in a heart failure model: in rats with preserved-ejection-fraction heart failure, 12 weeks of elamipretide improved leg muscle force and prevented fiber shrinkage.²⁹
• Skin cells: SS-31 loaded into milk-derived exosomes reduced ultraviolet damage in human skin fibroblasts more than SS-31 alone.³⁰ We found no human skin trial.
• Older adults: in 39 people aged 60 to 85, one 2-hour infusion raised peak muscle ATP production right after dosing (P = 0.045 for the percent change).¹³ All had poorly functioning muscle mitochondria at entry.¹³ Fatigue resistance did not improve, and no difference remained on day 7.¹³

How strong is the evidence

• FDA reviewers wrote in 2024 that some small early trials reported benefit, but later and larger trials did not confirm an effect on clinical outcomes.³
• The Barth syndrome gains came from 8 to 10 patients with no placebo group.¹ Developer employees co-wrote the extension report.¹⁷
• The inventor of SS-31 founded the developer, a conflict declared in one of the aging studies.¹²
• The human results come from elamipretide given in supervised clinical trials.³ Research-grade SS-31 is a different product, outside the approval.³¹

Related goal pages cover muscle growth, focus and memory, healing and recovery, blood sugar and skin and hair. Back to What is SS-31?, or read SS-31 side effects and SS-31 dosage.