SS-31 (elamipretide) is a four-amino-acid peptide that travels into mitochondria and binds cardiolipin, a fat that holds the cell’s energy machinery together.[1][6] In September 2025, the FDA granted it accelerated approval as Forzinity, the first treatment for Barth syndrome, a rare genetic disease.[3] Trials in other conditions, from heart attacks to macular degeneration, mostly missed their goals.[12][13][15]

This profile covers how SS-31 works, its FDA approval, what each trial found, its use in anti-aging, side effects and dosage.

What is SS-31?

SS-31 belongs to a family of “Szeto-Schiller” peptides designed by Hazel Szeto at Cornell and Peter Schiller in Montreal. Their alternating structure lets them pass into cells and concentrate about 1,000-fold in the inner mitochondrial membrane.[4] Its sequence is D-Arg-dimethyl-Tyr-Lys-Phe-NH2.[1] Stealth BioTherapeutics developed it as elamipretide, also called MTP-131 and Bendavia.[2]

How SS-31 works

Cardiolipin is a fat found almost only in the inner membrane of mitochondria, where it anchors the proteins that make ATP, the cell’s energy currency. SS-31 binds cardiolipin with high affinity.[5] That stops cardiolipin from turning cytochrome c into a damaging enzyme while letting it keep carrying electrons, which helps mitochondria keep producing energy under stress.[6] The FDA label describes it as improving mitochondrial structure and function.[1]

FDA approval for Barth syndrome

Barth syndrome is a rare inherited disorder of cardiolipin that causes heart muscle disease, muscle weakness and fatigue, affecting an estimated 1 in 300,000 to 400,000 people worldwide.[26]

  • Approved use: to improve muscle strength in adults and children with Barth syndrome weighing at least 30 kg.[1]
  • Accelerated approval: based on improved knee muscle strength, which FDA considers reasonably likely to predict real benefits like walking farther.[3]
  • Confirmatory trial required: a randomized, placebo-controlled trial in patients 5 and older, due to finish in 2029.[2][31]
  • A long road: FDA refused to review the first application in 2021 and declined to approve it in May 2025 before approving a resubmission in September 2025.[25][2]

SS-31 benefits: what the research shows

Barth syndrome

In the 12-patient TAZPOWER trial, the randomized, placebo-controlled part missed both primary goals.[7] In the open-label extension, 6-minute walk distance improved by about 96 meters by week 36, and the gain held to week 168 in the 8 patients who continued.[7][8] Compared with untreated patients from a natural history study, treated patients walked about 80 to 91 meters farther.[9]

Other conditions

ConditionResult
Primary mitochondrial myopathyPhase 3 trial in 218 adults missed its primary goals[12]; earlier smaller trials showed only trends[10][11]
Heart attackNo reduction in heart damage[13]
Heart failureNo significant change in heart function after 28 days[14]
Dry macular degenerationMissed primary goals; a phase 3 trial is under way[15][32]
Leber hereditary optic neuropathy (eye drops)No improvement in vision[16]

SS-31 for aging and energy

SS-31’s popularity in anti-aging circles comes from mouse studies:

  • Aged muscle: one dose restored mitochondrial energy production in 27-month-old mice within an hour, and eight days improved endurance.[18] Eight weeks reversed age-related declines and improved treadmill performance.[19]
  • Aged heart: eight weeks substantially reversed heart stiffening in old mice.[20]

In people, a single infusion in 39 adults aged 60 to 85 produced only a borderline improvement in muscle ATP production and no change in fatigue.[17] No trial has tested SS-31 for aging in humans over the long term.

SS-31 research around the world

  • Italy: in mice with a Barth syndrome-like defect, SS-31 improved the heart’s mitochondrial function.[21]
  • France: a 5-year-old with Barth syndrome treated under compassionate use saw heart pumping improve from 20% to 50% over six months and returned to school.[24]
  • China: a 2026 study found elamipretide improved egg quality and fertility in aged mice.[22]
  • Russia: a 2024 case report of an adult with Barth syndrome described elamipretide as an investigational option; the patient did not receive it.[33] Russian scientists also developed SkQ1, a different (non-peptide) mitochondria-targeted antioxidant that also protects cardiolipin, which was tested as eye drops for dry eye.[23][34]

SS-31 vs MOTS-c

Both are marketed as “mitochondrial peptides”, but they are very different. SS-31 is a lab-designed drug with many human trials and an FDA approval. MOTS-c is a natural signal made by mitochondria with no published human trials. SS-31 binds cardiolipin inside mitochondria; MOTS-c acts mainly on the cell’s energy-sensing pathways.

SS-31 side effects

From the Barth syndrome trial (12 patients each on drug and placebo):[1]

Injection-site reactionElamipretidePlacebo
Redness100%25%
Pain75%42%
Hardening67%17%
Itching67%17%
Hives25%0%
  • Allergic reactions: the label warns of serious allergic reactions, including rash and dermatitis, that can appear within minutes to months.[1]
  • Eosinophilia: a rise in eosinophils (a type of white blood cell) was common after 30 days, peaking around day 90 and returning to baseline within 6 to 12 months.[1]
  • Not for newborns: the vials contain benzyl alcohol.[1]
  • In other trials, injection-site reactions affected about 80% of participants.[11]

SS-31 dosage

SettingDose
Forzinity label (Barth syndrome, 30 kg or more)40 mg under the skin once daily; 20 mg with severe kidney impairment[1]
Most trials40 mg under the skin once daily[12][15]
IV studiesInfusions such as 0.05 mg per kg per hour[13]

The label requires a prescription and has no dosing for other uses. Gray-market “SS-31” is not the approved product, and its purity is unknown. For converting milligrams to syringe units, see our peptide calculator.

What users report

  • Prescription drug: elamipretide is FDA-approved as Forzinity for Barth syndrome only.[2]
  • Compounding: elamipretide does not appear on any of FDA’s compounding category lists.[27]
  • Sport: it is not named on WADA’s 2026 Prohibited List, which was finalized before its approval.[28]

This is general information, not legal advice.