SS-31
SS-31 targets the inner membrane of your mitochondria, where it binds a fat called cardiolipin to hold the energy machinery in alignment, reduce oxidative stress at its source, and preserve ATP output. It's the most clinically studied compound in the research-peptide space — and in 2025 it became the first mitochondria-targeted drug ever approved.
Overview
SS-31 is a four-amino-acid peptide (D-Arg-Dmt-Lys-Phe-NH₂) that concentrates inside mitochondria — specifically at the inner membrane, where energy production happens. It was discovered by Hazel Szeto's lab at Weill Cornell Medicine and developed as a drug under the name elamipretide.
Unlike almost everything else in this category, it has been through multiple Phase 2 and Phase 3 human trials. In September 2025 the FDA granted accelerated approval to elamipretide for Barth syndrome, a rare genetic mitochondrial disease — the first mitochondria-targeted therapeutic ever approved.
Key benefits
| Benefit | Description |
|---|---|
| Mitochondrial energy | Preserves electron-transport efficiency and ATP output, particularly when mitochondria are under stress. |
| Oxidative stress | Neutralizes superoxide and hydroxyl radicals at the inner membrane, where they're generated, rather than after they've dispersed. |
| Membrane integrity | Binds cardiolipin to maintain cristae structure — the folded architecture that holds the energy machinery in working order. |
| Cell survival | Reduces cytochrome-c release and caspase-3 activation in neuronal and cardiac cell models — the signaling that drives cells to die under stress. |
| Cardiac function | Studied for heart function and ischemia-reperfusion injury, where mitochondrial damage is a central driver. |
| Inflammation | Lowers pro-inflammatory markers including IL-1β and TNF-α in preclinical tissue models. |
Mechanisms of action
Mitochondria generate energy along a chain of protein complexes embedded in their inner membrane. That membrane is folded into structures called cristae, and a phospholipid called cardiolipin holds the folds in shape and keeps the complexes properly assembled next to each other.
When cardiolipin is damaged — by age, disease, or oxidative stress — the architecture loosens. Electrons leak out of the chain instead of passing cleanly down it. Output drops, and the escaped electrons form reactive oxygen species, which damage more cardiolipin. It's a feedback loop.
SS-31 carries a positive charge that draws it into mitochondria, where it binds cardiolipin directly.
What that produces
Cristae keep their shape and the transport complexes stay properly assembled.
A tighter chain means fewer escaped electrons, so fewer reactive species get made in the first place.
Energy output holds up better under metabolic or ischemic stress.
Less cytochrome-c escapes the membrane, which is the trigger for the cell's self-destruct pathway.
Think of a cell as a ship.
Down in the hull are the engine rooms — the mitochondria. Inside each one, the machinery is bolted to the walls in a very particular arrangement, and the whole thing is held together by gaskets.
Those gaskets are cardiolipin.
When they're new, everything sits tight. Power flows through the machinery cleanly, end to end, and comes out as usable energy.
But gaskets wear out. As they crack, the machinery shifts out of alignment and starts throwing sparks. You lose power — and worse, the sparks burn the gaskets around them. Which makes more sparks. Which burns more gaskets.
SS-31 is the repair crew for those gaskets. It goes straight down to the engine rooms, seals the leaks, and gets the machinery seated properly again. Power output steadies, and the sparks stop before they start.
Considerations
SS-31 has better human evidence than nearly anything else in this category — and a more complicated record. The FDA approval covers Barth syndrome, a genetic disease affecting roughly 150 people in the United States that damages cardiolipin directly. It came through the accelerated pathway, based on improved knee-extensor strength — a marker considered likely to predict benefit rather than proof of it.
Trials in broader populations have not produced approvals. A Phase 3 in mitochondrial myopathy missed both primary endpoints across 218 patients, though the prespecified subgroup with nuclear-DNA mutations did improve on walking distance. A follow-up trial built specifically around that subgroup completed in late 2024; results haven't been published. Trials in heart failure missed their endpoint, and work in dry macular degeneration is ongoing.
Every human trial used 40–60 mg daily. Community protocols typically run 1–5 mg — roughly ten times lower.
Every trial enrolled people with diagnosed mitochondrial disease. None tested healthy adults for energy or longevity.
Entirely renally excreted. The approved label halves the dose in severe renal impairment.
3–4 hours, with almost no accumulation between daily doses. Timing consistency matters more than with a long-acting compound.
Not an occasional issue — the dominant adverse event across the whole clinical program.
Stabilizing the machinery does nothing if the parts it runs on are missing. See what it needs to work.
What it needs to work
SS-31 protects the machinery. It doesn't supply what the machinery runs on. That's a different requirement from a compound that tells your body to build — this one is about operating supplies rather than construction materials.
Sealing the gaskets doesn't help if the fuel lines are empty or the parts are missing. Every item below is a physical component or cofactor of the electron transport chain that SS-31 is stabilizing.
The mobile electron carrier inside the chain SS-31 protects. If it's depleted, stabilizing the housing doesn't restore function — the carrier itself is what's missing. Absorbs better with fat.
The chain starts at Complex I, and NAD+ is what feeds it. No NAD+, no electrons entering the system. Poorly absorbed orally — NR or NMN are the usual route.
Converts to FAD, the cofactor for Complex II and the flavoproteins that hand electrons into the chain from fat metabolism.
Rarely mentioned, and it's the most direct one: cardiolipin — the exact molecule SS-31 binds — is built largely from linoleic acid. The target is made from dietary fat.
Iron-sulfur clusters do the actual electron handoffs through Complexes I, II, and III. Deficiency degrades the chain regardless of how stable the membrane is.
ATP functions in the body as Mg-ATP. Producing more ATP is only useful if there's magnesium to pair it with.
The research, in detail
- Cell assaysROS scavengingLocalizes to the inner mitochondrial membrane and neutralizes superoxide and hydroxyl radicals at the site of production.
- Isolated mitochondrial preparationsATP productionPreserves electron-transport efficiency and increases ATP yield under stress conditions.
- Ischemia–reperfusion modelsMembrane stabilizationInteracts with cardiolipin to maintain cristae structure and mitochondrial integrity.
- Neuronal & cardiomyocyte culturesAnti-apoptotic signalingReduces cytochrome-c release and caspase-3 activation.
- Preclinical tissue modelsInflammatory markersLowers IL-1β and TNF-α.
- Humans — Barth syndrome, approvedTAZPOWER12-week randomized crossover at 40 mg/day, then an open-label extension up to 192 weeks. FDA accelerated approval granted September 2025 on improved knee-extensor strength.
- Humans — Phase 3, missed endpointsMMPOWER-3218 patients, 40 mg/day, 24 weeks in mitochondrial myopathy. Missed both primary endpoints. The prespecified nuclear-DNA subgroup improved 25 meters on the six-minute walk versus placebo (P = .03), which prompted a follow-up trial at 60 mg.
- Humans — Phase 2, missed endpointPROGRESS-HF71 patients with reduced ejection fraction, 4 mg or 40 mg versus placebo over 28 days. No significant difference in cardiac volumes.
- Humans — Phase 3, ongoingReNEWDry age-related macular degeneration, 40 mg daily for 96 weeks. Active, not recruiting.
What it feels like
Reports skew toward steadier endurance and less of the flat, drained feeling that shows up under sustained physical or cognitive load. It isn't described as stimulating — there's no lift, no edge, nothing that arrives within an hour of injecting.
The most consistently reported sensation isn't an effect at all — it's the injection site. Warmth, redness, itching, occasionally a small firm bump that lingers. Expect that rather than being surprised by it.
Dosing
| Parameter | Reported |
|---|---|
| Clinical trial dose | 40 mg daily |
| Follow-up trial dose | 60 mg daily |
| Commonly reported dose | 1–5 mg |
| Frequency | Daily |
| Cycle length | Trials ran continuously |
| Half-life | 3–4 hours |
| Route | Subcutaneous |
Mixing & storage
Storage
Stable long-term. Keep sealed until you're ready to reconstitute.
Refrigerate at 2–8°C. More forgiving than MOTS-c, but not indefinite.
Repeated freeze-thaw cycles degrade it. Aliquot if you're freezing reconstituted product.
Solution should be clear. Particulates or persistent cloudiness mean don't use it.
Side effects
Injection site reactions dominate. Redness, warmth, itching, and small firm bumps that can persist. This is the most common adverse event in every trial of this compound, and it's common enough that it has been studied in its own right.
Why it happens — and what helps
Research found that elamipretide activates MRGPRX2, a receptor on mast cells. Triggering it releases histamine and drives local inflammation. That makes it a direct pharmacological effect rather than an allergy or a contamination problem.
In a Phase 1 crossover, topical mometasone applied before injecting significantly reduced reactions — without changing plasma levels of the drug.
Ice reduced pain, but also lowered peak concentration and total exposure. It costs you some of the dose.
Standard practice, and it matters more here given how persistent the bumps can be.
Rapid injection tends to provoke a stronger local response.
Beyond the injection site, tolerability was described as good across the clinical program, including long-term use past three years in the Barth extension study. Other reported effects are mild: headache, nausea, occasional dizziness.
Hives spread beyond the injection site, your face or throat swells, breathing changes, or you feel faint. That's systemic, not local — a different situation entirely.
Sourcing
SS-31 is unusual in that an approved pharmaceutical version exists. What's sold as a research compound is not that product, and is only as good as the supplier.
Lot number should match your vial. A generic PDF reused across the catalog isn't a COA.
The actual chart, not just a "99%" claim on a graphic. Standard spec is ≥99% purity.
Reported in EU/mg, typically under 0.1. Often missing — that absence is information.
Peptides degrade with heat. If it arrives warm after days in transit, that matters.
Common questions
Is SS-31 approved?
The pharmaceutical version, elamipretide, was approved in September 2025 for Barth syndrome — one rare genetic disease affecting about 150 people in the US. SS-31 sold as a research compound is a different thing and is not approved for human use.
Why is the trial dose so much higher than what people use?
Trials used 40–60 mg daily in people with genetic mitochondrial disease under clinical monitoring. Community protocols run roughly ten times lower. Nobody has published a study at the lower amounts, so the gap is unexplained rather than resolved.
Why does the injection site react so much?
SS-31 activates MRGPRX2 on mast cells, which releases histamine locally. It's a direct effect of the compound, not an allergy. Topical corticosteroid before injecting has been shown to help.
How long before I notice anything?
Protection is harder to feel than stimulation — you'd be noticing an absence of decline rather than a positive effect. Trials measured over weeks to months, not days.
Does it need cycling?
The clinical trials dosed continuously for 24 weeks and beyond, some out past three years. Community protocols commonly cycle 8 weeks on and off, but that convention doesn't come from trial data.
Can I take it with other peptides?
People do. There's no human data on any combination, so nobody can tell you how they interact.
