Short answer: SS-31 is the research name for elamipretide, a small peptide that binds cardiolipin in the inner membrane of mitochondria. It is now an FDA-approved drug: Forzinity (initial US approval 2025) is indicated to improve muscle strength in people with Barth syndrome, a rare genetic disease, who weigh at least 30 kg. That approval is an accelerated approval based on knee muscle strength, and it needs confirmation. In the 12-week randomized part of the Barth trial, elamipretide did not beat placebo on its main goals, and a 218-patient phase 3 trial in primary mitochondrial myopathy also missed its main goals. There is no trial evidence for energy, longevity or fitness use in healthy people.
SS-31 is sold online as a "mitochondrial peptide" for energy and anti-aging. Unlike most research peptides, it has a real drug behind it, with a label and controlled trials. That makes it a useful case: we can see exactly what was proven, for whom, and what was not.
What SS-31 is
SS-31 and elamipretide are the same molecule. The Forzinity label calls it "a mitochondrial cardiolipin binder that localizes to the inner mitochondrial membrane and improves mitochondrial morphology and function." Mitochondria are the parts of cells that make energy, and cardiolipin is a lipid in their inner membrane. The label describes the drug substance as the hydrochloride salt of a four-amino-acid peptide (D-arginyl-2,6-dimethyl-L-tyrosyl-L-lysyl-L-phenylalaninamide).
The FDA approval: Forzinity for Barth syndrome
Barth syndrome is a rare X-linked disorder. A quality-of-life study in affected boys and men describes it as "characterized by cardiomyopathy, neutropenia, growth abnormalities, and skeletal myopathy" (Kim 2022). Key points from the Forzinity label:
- Initial US approval: 2025.
- Indication: "to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg."
- Approval type: accelerated approval "based on an improvement in knee extensor muscle strength, an intermediate clinical endpoint." Continued approval "may be contingent upon verification and description of clinical benefit in a confirmatory trial."
- How it is given: a daily subcutaneous injection in the abdomen or outer thigh, rotating sites. Vials are discarded 8 days after first opening. The label's dose is for that indication only; we are not giving dosing advice.
- Most common side effects: injection-site reactions, including redness, pain, hardness, itching, bruising and hives.
- Pharmacokinetics: peak levels 0.5 to 1 hour after a subcutaneous dose, with about 92% bioavailability.
What the Barth trial actually found
The label's clinical studies section is unusually frank. The evidence came from a randomized, double-blind, placebo-controlled crossover trial (TAZPOWER) and its long open-label extension:
- The randomized part enrolled 12 subjects aged 12 or older for 12 weeks of treatment.
- Its primary endpoints were the 6-minute walk distance and a total fatigue score. Elamipretide "was not superior to placebo on these primary endpoints."
- Knee extensor strength was a secondary endpoint. Increases "were not observed during the randomized trial but were observed during the extension period," in which 10 subjects continued and 8 took part through week 168.
So the approval rests on muscle strength gains seen over years of open-label treatment in a handful of patients with a rare disease that has few options. That is a reasonable basis for an accelerated approval in that setting. It is not evidence about anyone else.
The phase 3 trial that missed
Elamipretide was also tested in primary mitochondrial myopathy, a broader group of genetic muscle diseases. The MMPOWER-3 trial randomized 218 participants to elamipretide or placebo by daily subcutaneous injection for 24 weeks (Karaa 2023). It "did not meet its primary endpoints": the difference in 6-minute walk distance was -3.2 meters (95% CI -18.7 to 12.3; p = 0.69), and the fatigue score difference was also not significant.
The people in that trial were adults (mean age 45.6; 64% women), and most (74%) had mitochondrial DNA changes, the rest nuclear DNA defects. By contrast, the Barth syndrome trial population was 12 young males (mean age 19.5) whose symptoms ranged from mild to very severe (Gwaltney 2025). Neither group resembles a healthy adult looking for more energy.
From a rare-disease drug to a "wellness peptide"
The gap between the evidence and how SS-31 is marketed is wide:
- Different people. All trials above were in people with genetic mitochondrial disease. None tested healthy adults for energy, endurance, aging or recovery.
- Mixed results even there. Primary endpoints were missed in both the Barth randomized phase and MMPOWER-3.
- Different product. Forzinity is a sterile, preserved solution made under FDA manufacturing rules. A powder sold as "SS-31, research use only" is not Forzinity. In an August 2026 warning letter, FDA named an online seller's "SS-31 (Elamipretide)" among products it considered unapproved new drugs. See what "research use only" means and how to read a COA.
Other label details worth knowing
- The label reduces the dose for adults with severe kidney impairment, so kidney function matters.
- Forzinity contains benzyl alcohol as a preservative and is not approved for use in newborns because of the risk of serious reactions to benzyl alcohol in that age group.
- In drug-interaction studies, elamipretide did not change the effects of aspirin, clopidogrel or heparin.
Questions worth asking before using SS-31
- Is there a diagnosis that matches what the drug was tested for? If not, what is the expected benefit based on?
- Is the product the FDA-approved drug, a compounded product, or a research powder? Each has very different quality checks.
- How is your kidney function? The label adjusts the dose in severe kidney impairment.
- What will you measure to decide whether it is working, and when will you stop if it is not?
- Who will you report side effects to? The label lists injection-site reactions as the most common problem, so note any redness, hardness or itching by site and date.
If you use it
If you are prescribed Forzinity, follow your care team's instructions and the label. If you are using SS-31 outside that setting, know that no trial supports it, and keep careful records: product and lot, reconstitution or opening date, each injection and site, and any reactions. The Forzinity label's 8-day discard rule after opening applies to that product only; research powders have no tested shelf life once mixed (see how long reconstituted peptides last). Dose Track tracks each vial from the day you open or mix it and logs site rotation for daily injections.
Frequently asked questions
Is SS-31 the same as elamipretide?+
Yes. SS-31 is the research name for elamipretide, the active ingredient in Forzinity.
Is elamipretide FDA approved?+
Yes. Forzinity (elamipretide), initial US approval 2025, is indicated to improve muscle strength in adults and children with Barth syndrome weighing at least 30 kg. It is an accelerated approval based on knee extensor strength, and continued approval may depend on a confirmatory trial.
Did elamipretide work in trials?+
Partly. In the 12-week randomized Barth syndrome trial it did not beat placebo on walking distance or fatigue. Knee strength improved during the long open-label extension. In the 218-patient MMPOWER-3 trial in primary mitochondrial myopathy, it missed its primary endpoints.
Does SS-31 work for energy or anti-aging?+
There are no trials of SS-31 in healthy people for energy, endurance, aging or recovery. All the trials discussed here were in people with genetic mitochondrial diseases.
What are the side effects of elamipretide?+
The Forzinity label lists injection-site reactions as the most common: redness, pain, hardness, itching, bruising and hives.