For most of what it has been tested on, no. A trial in 218 adults with an inherited muscle disease found people walked 3.2 metres less far than on a dummy injection; trials in heart failure, in heart attack and in 176 people with an eye disease all missed what they set out to change. The one place it is approved is Barth syndrome, an ultra-rare genetic condition, and even there the randomised part of the trial showed nothing — the leg strength the approval is based on only rose afterwards, when everyone knew they were taking it and there was nobody left to compare against.

Is SS-31 FDA approved?

Yes, since 19 September 2025, under the brand name Forzinity and for one condition only: improving muscle strength in adults and children with Barth syndrome who weigh at least 30 kilograms. It was approved on the accelerated pathway, which means the regulator accepted a stand-in measurement — knee strength — rather than proof that people are better off, and required the company to run a proper controlled trial afterwards to check. That trial began recruiting in 2026 and is not due to finish until 2029. It is approved for nothing else, anywhere.

Is SS-31 approved in Europe?

No. There is no European marketing authorisation for elamipretide and no European public assessment report, which means no licensed product exists to prescribe or buy in the EU. What does exist is orphan status — a designation the European Medicines Agency granted for Barth syndrome on 20 May 2021 and for a mitochondrial DNA depletion disease on 16 May 2022. Orphan status is regulatory support for developing a medicine; the agency states plainly that it does not mean the medicine is available or authorised.

What are the side effects of SS-31?

The one everybody gets is a reaction where the needle goes in — redness, hardening, itching, pain, bruising or hives. All twelve people in the trial had one on the drug, against eight of twelve on a dummy injection. A type of white blood cell linked to allergy rises often in people treated for more than a month and settles again over six to twelve months. The serious one is a genuine allergic reaction, which can start minutes after a dose or months in, and which means never taking it again. Nobody has ever run a cancer study of it in animals or in people; the regulator ordered two in animals as a condition of approval, with the longer one not reporting until 2030.

SS-31 vs MOTS-c — what is the difference?

Both are short peptides sold online as mitochondrial or anti-ageing compounds, and their evidence could hardly be further apart. SS-31 has been through more than a dozen registered human trials including two of phase 3 size, and is an approved medicine in the United States for one ultra-rare disease — while failing its biggest trials. MOTS-c has no approval anywhere and is on the World Anti-Doping Agency's prohibited list by name, as a metabolic modulator. What they share is that neither has ever been shown to slow ageing or add strength in a healthy person.

In the United States, with a prescription, as Forzinity — and only if you have genetically confirmed Barth syndrome and weigh at least 30 kilograms. It has been on sale there since 4 December 2025 through a single specialty pharmacy. In the EU there is no licensed product at all. Vials sold online as SS-31 for research are outside every part of that: nobody has checked what is in them, and a 2026 review in Sports Medicine describes exactly this grey market operating without regulatory oversight. This register does not link sellers and does not tell anyone how to use anything.

Is SS-31 banned in sport?

Not by name, and as of the 2026 list not at all, as far as can be established from the list itself. Elamipretide appears nowhere in the World Anti-Doping Agency's 2026 Prohibited List. Until September 2025 it would have been caught by the list's catch-all for substances with no approval from any health regulator anywhere; the US approval removed it from that category three months before the 2026 list took effect. An athlete should still check with their own anti-doping body rather than rely on this reading.

Does SS-31 do anything for ageing?

One study has looked, and it is very thin. Thirty-nine healthy people aged 60 to 85 got a single two-hour drip; straight afterwards, one hand muscle was making energy 27 per cent faster than before, against 12 per cent in the group given salt water. A week later the difference had disappeared, and how long that muscle could keep contracting had not changed at all. The study was funded by the manufacturer. A 30-person open pilot in older adults with no comparison group was still running in 2026. Nothing has been measured about lifespan, frailty or strength in a healthy person.

Why was SS-31 approved if its big trial failed?

Because Barth syndrome is a different question from the diseases the big trials were run in, and because it affects about 130 people in the United States, so a large trial is not really possible. The FDA refused to even file the application in 2021, on the grounds that no adequate controlled trial supported it, and the company resubmitted without running the new trial the agency had asked for. An expert committee voted 10 to 6 that the drug was effective, with several of the yes votes saying openly that they were using regulatory flexibility and that the uncertainty was large. The FDA then declined once, in May 2025, before approving in September on the accelerated pathway with a confirmatory trial required.

Therapeutic

SS-31 (elamipretide)

Also known as Elamipretide · Elamipretide hydrochloride · Forzinity · MTP-131 · MTP131 · Bendavia · SS31 · SS 31 · SS-31 peptide · Szeto-Schiller peptide 31 · Szeto-Schiller 31 · D-Arg-Dmt-Lys-Phe-NH2 · D-Arg-2,6-dimethyltyrosine-Lys-Phe-NH2 · elamipretid · elampretide · elamiprotide · mitochondrial peptide SS-31 · cardiolipin-binding peptide SS-31

Approved medicine

21 of 51 peptides sit at this level

Category: Therapeutic
Doping status: Not banned in sport
Sources: 29

SS-31, better known to regulators as elamipretide, is a chain of four amino acids that sticks to a fat called cardiolipin inside the tiny power plants of your cells. Since 19 September 2025 it has been an approved prescription medicine in the United States, sold as Forzinity, for exactly one thing: improving muscle strength in people with Barth syndrome, an inherited disease that affects roughly 130 people in the whole country. That approval sits on top of a long run of failures — a 218-person trial in a different mitochondrial muscle disease found it no better than a dummy injection, and so did trials in heart failure, in heart attack and in 176 people with an eye disease. It is not approved anywhere in Europe, and everything sold online as SS-31 is outside all of that.

SS-31 (elamipretide)What it is

What it is
Sold and legal
In your body
What changed
What can go wrong
Amounts studied
What people say
Unknowns
Questions
Sources

What it is

A chain of only four amino acids, made in a laboratory, that has carried a different name at every stage of its life: SS-31 in the papers of the group that invented it, MTP-131 or Bendavia in the old heart trials, elamipretide as its official drug name, and Forzinity as the brand it is sold under in the United States. It carries a positive charge, is drawn into the tiny power plants inside cells, and sticks to a fat in their inner wall. Since 19 September 2025 it has been an approved American prescription medicine for one ultra-rare inherited disease, Barth syndrome, and for nothing else anywhere in the world. The sequence field is left empty on purpose, for the reason given in the evidence note.

How it is sold, and whether it is legal

Sold as: Injection under the skin of the belly or outer thigh, once a day. The approval covers only people weighing at least 30 kg. Earlier trials in heart attack and in older adults used a drip into a vein; the approved product is not for intravenous use.
Legal status in the EU: Not an approved medicine in the EU. There is no marketing authorisation and no European public assessment report for elamipretide. What exists is orphan designation, granted for Barth syndrome on 20 May 2021 (EU/3/21/2430) and for myopathic mitochondrial DNA depletion syndrome on 16 May 2022 (EU/3/22/2614), and the European Medicines Agency states plainly on both pages that designation does not mean a medicine is available or authorised. In the United States it has been an approved prescription medicine since 19 September 2025 under NDA 215244, sold as Forzinity, and commercially available since 4 December 2025 through a single specialty pharmacy. On doping: elamipretide is not named anywhere in the WADA 2026 Prohibited List. Until the September 2025 approval it was caught by section S0, which prohibits any substance with no current approval by any governmental regulatory health authority for human therapeutic use; the US approval took it out of that class three months before the 2026 list came into force. That is a reading of the list rather than an entry in it, and an athlete should confirm it with their own anti-doping body.

What it does in your body

9 parts of the body · 5 measured in people, 2 from one small study, 1 only seen in animals, 1 only seen in a dish

It concentrates in the inner wall of mitochondria — the compartments that turn food and oxygen into usable energy — and binds tightly to cardiolipin, the fat that holds that wall's deep folds in shape. In isolated mitochondria and in animal tissue this stops the folds collapsing when oxygen runs short and speeds up the return of energy production afterwards; in model membranes it works by changing the electrical charge at the membrane surface rather than by mopping up damaging molecules, which is how the earliest papers described it. The approved label puts it in one line: a mitochondrial cardiolipin binder that localises to the inner mitochondrial membrane and improves mitochondrial shape and function. Almost none of that chain has been demonstrated inside a living person. The one human measurement is a temporary rise in one hand muscle's rate of energy production after a single two-hour drip in 39 older adults, which had disappeared a week later.

How far people can walk: This is the measure the whole programme was built on, and it did not move. In the trial the approval came from, twelve people with Barth syndrome walked 443.1 metres after twelve weeks on elamipretide and 443.9 metres after twelve weeks on a dummy injection. In the much larger trial in adults with a different inherited muscle disease, 109 people on the drug and 109 on a dummy injection ended 3.2 metres apart, in the dummy injection's favour. Both people and their doctors improved on this test simply by being in a trial: in one of the two orders of the Barth crossover, the group on the dummy injection gained 60 metres.; Measured in a randomised crossover trial of 12 people with Barth syndrome over two 12-week periods, and in a randomised trial with a dummy-injection group in 218 adults with primary mitochondrial myopathy over 24 weeks.; Measured in people; Source [04]Source [06]Source [08]
The heart: Nothing measurable, in the two places it was properly tested. In 71 people with a weak heart pump, four weeks of either a small or a full daily injection left the volume of blood sitting in the heart after each beat no different from a dummy injection. In people having a heart attack, a drip of the compound during the procedure to reopen the artery did not shrink the damaged area of heart muscle. In Barth syndrome, some heart measurements did shift over the uncontrolled years of the extension, but the regulator's own review says those measurements have no known relationship to how patients actually fare and were not a fair basis for judging the drug.; Measured by heart scan in a randomised trial with a dummy-injection group in 71 adults with heart failure over 4 weeks, and by a blood marker of heart muscle damage in a randomised heart attack trial of 300 people, 152 on the drug and 148 on a dummy infusion.; Measured in people; Source [04]Source [10]
The back of the eye: In 176 people with the dry form of age-related macular degeneration, neither of the two things the trial set out to change actually changed: vision in dim light, and the size of the patch of dying tissue at the back of the eye. What did look better was a thin layer of the retina packed with power plants, which broke down about 43 per cent more slowly than on a dummy injection — but that was one of several extra measurements, and its statistical result carries no protection against chance. The regulator has since agreed to let that layer be the main measure in a 313-person trial now running, which will not report before September 2027.; Measured by eye scan and dim-light vision testing in a randomised trial with a dummy-injection group, 117 people on elamipretide and 59 on a dummy injection, over 48 weeks.; Measured in people; Source [09]Source [20]
The skin where the needle goes in: This is what taking it actually feels like. Every single one of the twelve people in the Barth trial got a reaction at the injection site while on elamipretide — redness in all twelve — against eight of twelve while on the dummy injection, with redness in three. Hardening, itching, pain, bruising and hives all turned up more often on the drug. It is a daily injection, indefinitely, which is why this matters more than a percentage suggests. It also made the trial partly guessable: the regulator's review notes that people could work out which arm they were on from whether their skin reacted, on a test that depends on how hard they try.; Counted in all 12 people in the randomised crossover trial, across both the elamipretide and the dummy-injection periods.; Measured in people; Source [01]Source [04]
A type of white blood cell: One blood count often goes up. In studies where the injections lasted 30 days or more, the label records that the number of eosinophils — the white cells that rise in allergy and in parasite infection — frequently increased, peaking around 90 days after the first dose and drifting back to normal after six to twelve months of continued treatment or after stopping. Nobody felt anything from it and no other blood test changed alongside it. The label reports it as a finding rather than as a problem.; Measured by blood test across the studies in which elamipretide was given for 30 days or longer, and reported in the approved US product information.; Measured in people; Source [01]
Leg strength, in Barth syndrome: This is the one thing the medicine is approved for, and the honest version of it has two halves. In the randomised half of the trial, the strength of the muscle that straightens the knee rose by 4.7 newtons on elamipretide and by 6.2 newtons on the dummy injection — no advantage, and if anything the dummy injection did slightly better. Strength only started rising in the years afterwards, when everyone knew they were on the drug and there was nobody left to compare them with: a median gain of 34 newtons at twelve weeks of that open phase in the ten who were left, and 63 newtons at week 168 in the eight still there. The approval was granted on the second half, labelled by the regulator as an intermediate measure rather than proof of benefit, with a proper controlled trial required afterwards to check whether it means anything.; Measured with a handheld strength meter in 12 people with genetically confirmed Barth syndrome during a randomised crossover trial, then in the 8 to 10 of them who continued into an open extension with no comparison group, for up to 192 weeks.; One small study; Source [01]Source [04]
Muscle energy in older people: One thing has been measured in ordinary older adults, and it is very small. Thirty-nine healthy people aged 60 to 85, picked because their muscle power plants were already working poorly, had a two-hour drip of elamipretide or of salt water. Straight afterwards, the maximum rate at which a small hand muscle could make energy had risen 27 per cent in the drug group against 12 per cent in the placebo group. Seven days later there was no difference left. How long the muscle could keep contracting before tiring — the thing a person would actually notice — did not change. The study was paid for by the manufacturer.; Measured by magnetic resonance and optical scanning of the first muscle between thumb and index finger, in 39 healthy adults aged 60 to 85, after a single two-hour infusion, with a salt-water comparison group.; One small study; Source [11]
The kidneys: Almost everything here is from pigs. In animals with a narrowed kidney artery, elamipretide restored blood flow and filtering and reduced scarring. The one human study was a pilot in 14 people having a blocked kidney artery opened up; the regulator's own summary of it records that the change in kidney filtering was reported as significant in the treated people, and that this change was never compared against the people who received a dummy infusion. That is not a result.; Measured in pigs with experimentally narrowed kidney arteries, and in a randomised pilot of 14 adults in which, by the regulator's account, the treated group was not compared with the comparison group.; Only seen in animals; Source [04]Source [21]
The power plants inside your cells: Every cell contains hundreds of tiny compartments that turn food and oxygen into usable energy. Their inner wall is folded into deep pleats, and those pleats are held in shape by a fat called cardiolipin. SS-31 carries a positive charge, gets pulled into that inner wall, and sticks to cardiolipin there. In isolated mitochondria and in animal tissue this keeps the pleats from collapsing during oxygen starvation and speeds up the return of energy production afterwards. The approved label describes it in one sentence: a mitochondrial cardiolipin binder that localises to the inner mitochondrial membrane and improves mitochondrial shape and function.; Binding measured with a fluorescent version of the compound in isolated mitochondria and in rat kidney; the physical effect on membranes measured in model bilayers and in mitochondria taken from animals. No part of this was measured in a living person.; Only seen in a dish, not in a body; Source [01]Source [12]Source [19]

What changed when it was measured

10 findings · 4 measured in people, 6 from one small study

Its largest trial failed. MMPOWER-3 randomised 218 adults with primary mitochondrial myopathy and found they walked 3.2 metres less far than people on a dummy injection (95 per cent confidence interval −18.7 to 12.3, p = 0.69), with no difference in fatigue either; the trial registry record is terminated, and the reason it gives is that the double-blind portion did not meet the primary endpoints. The rest went the same way: 176 people with dry macular degeneration missed both main measures, 71 people with a weak heart pump showed no change in heart volumes, and treatment during a heart attack did not shrink the damaged muscle. Despite all of that, this is an approved medicine — the US regulator granted Forzinity accelerated approval on 19 September 2025, to improve muscle strength in adults and children with Barth syndrome weighing at least 30 kg. The register's top rung is defined as approval after large randomised trials, and that clause does not describe this approval: the trial had 12 participants, both of its primary endpoints were missed, and knee extensor strength — the very measure the approval rests on — rose 4.7 newtons on elamipretide against 6.2 newtons on the dummy injection (p = 0.65) in the only randomised comparison. Strength rose only in the uncontrolled open-label extension that followed, in eight people, with the pre-dose visit of the failed trial as the baseline. The FDA refused even to file the application in 2021 for lack of an adequate controlled trial, the company resubmitted without running the new trial the agency recommended, an advisory committee split 10 to 6, and a first decision in May 2025 declined approval before the September 2025 accelerated approval. A randomised confirmatory trial is required as a condition and does not report until 2030. The sequence field is null because it cannot be written honestly: the chain is D-arginine, 2,6-dimethyltyrosine, lysine and phenylalanine with an amide cap, which contains a D-amino acid, a residue that has no letter in the standard one-letter code, and a capped end — so any standard code would name a different molecule.

The compound moves fast and leaves fast. Levels in the blood peak half an hour to an hour after an injection under the skin, about 92 per cent of what is injected reaches the bloodstream, and within 48 hours essentially all of it has come out in the urine as either the compound or two broken-down pieces that do nothing. In older adults given a single drip, the rise in muscle energy production was there immediately and gone by day 7. What that means for the effects people care about is unresolved: in Barth syndrome nothing separated from a dummy injection over 12 weeks, and the strength gains appear on a chart that only starts once the comparison group has been removed, running from week 12 to week 168 in eight people. The longest anyone has been followed with a comparison group is 48 weeks, in the eye trial and in the unreported nuclear-DNA trial; in Barth syndrome itself the comparison lasted 12 weeks.

How far people could walk, in mitochondrial myopathy: Nothing. After 24 weeks the difference between elamipretide and a dummy injection was −3.2 metres (95 per cent confidence interval −18.7 to 12.3, p = 0.69) — that is, the dummy injection side was very slightly ahead. Fatigue scores came back the same way, a difference of −0.07 (p = 0.37). The paper classes this as the strongest grade of evidence that the drug does not improve either measure.; 218 adults with genetically confirmed primary mitochondrial myopathy, average age 45.6, 64 per cent women; 109 received elamipretide and 109 a dummy injection, and neither they nor the staff knew which.; Measured in people; Source [06]Source [07]
The heart's pumping volume in heart failure: No difference. Over four weeks the amount of blood left in the heart after each beat changed by −0.3 millilitres on the low amount and +2.3 on the full amount, compared with a dummy injection — neither anywhere near a real difference (p = 0.90 and p = 0.28). The heart's pumping fraction did not separate either.; 71 adults with a weak heart pump, average age 65, average pumping fraction 31 per cent; split three ways between a dummy injection, a low amount and the full amount.; Measured in people; Source [10]
Damage to the heart muscle after a heart attack: No reduction. The blood marker of dead heart muscle, added up over the three days after the artery was reopened, came to 5,570 on the drug against 5,785 on a dummy infusion — a difference the paper reports as not significant. Nothing else the trial had planned to look at — heart scans, artery pictures, heart tracings or how patients fared — moved either.; 300 adults having their first heart attack of this type, 152 given the drug and 148 a dummy infusion, by the trial registry's own posted results.; Measured in people; Source [18]Source [22]
Vision and retinal damage in dry macular degeneration: Both main measures missed: dim-light vision and the size of the dying patch at the back of the eye were no better than on a dummy injection over 48 weeks. Among the extra measurements, the breakdown of a power-plant-rich retinal layer was 43 per cent slower than on the dummy injection, and 14.6 per cent of treated people gained ten letters or more of dim-light vision against 2.1 per cent — both carrying only unprotected p-values, which means chance has not been ruled out.; 176 people aged 55 and over with dry age-related macular degeneration and a non-central patch of atrophy; 117 on elamipretide, 59 on a dummy injection.; Measured in people; Source [09]
Leg strength, in the randomised half of the Barth trial: No advantage. The strength of the muscle that straightens the knee rose 4.7 newtons on elamipretide and 6.2 newtons on the dummy injection after 12 weeks (p = 0.65). None of the other secondary measures separated either — balance, sit-to-stand, patient and doctor impressions and a fatigue questionnaire all came back between p = 0.21 and p = 1.00.; 12 males aged 12 to 35 with genetically confirmed Barth syndrome, each of whom took both elamipretide and a dummy injection for 12 weeks in a random order, with a 4-week gap between.; One small study; Source [01]Source [04]
Leg strength, in the open years afterwards: This is the number the approval rests on, and it has no comparison group at all. Measured against where people stood before their very first dose, the median gain was 34 newtons at week 12 of the open phase, 68 at week 24, 41 at week 48 and 63 at week 168. Everyone knew they were taking the drug, everyone who was still there had chosen to stay, and eight people were left by the end. The regulator labelled this an intermediate measure and required a proper controlled trial to find out whether it corresponds to anything a patient would feel.; 10 of the original 12 continued into the open extension; 8 reached week 168 and 3 reached week 192. Two left because of side effects.; One small study; Source [01]Source [02]
How far people could walk, in Barth syndrome: 443.1 metres on elamipretide against 443.9 metres on a dummy injection after 12 weeks — a difference of −0.8 metres, p = 0.97. Both sides improved a lot from where they started, which is the point: in one of the two orders the trial was run in, the people on the dummy injection gained about 60 metres.; 12 males aged 12 to 35 with genetically confirmed Barth syndrome, each taking both treatments in a random order.; One small study; Source [04]Source [08]
Fatigue, in Barth syndrome: Fatigue scores fell 1.4 points on elamipretide and 1.2 points on the dummy injection over 12 weeks, a difference of 0.2 points, p = 0.70. With both of the trial's two main measures missed, the statistical budget was spent, and none of the secondary measures could be formally tested at all.; The same 12 people with Barth syndrome, scored on a symptom questionnaire built for the disease.; One small study; Source [04]
Energy production in an ageing hand muscle: Rose 27 per cent immediately after a single two-hour drip, against 12 per cent in people given salt water (p = 0.045 for the percentage change, p = 0.055 for the raw change). By day 7 the difference was gone. How long the muscle could keep contracting before tiring did not change.; 39 healthy adults aged 60 to 85 with already poorly functioning muscle power plants; 19 received elamipretide and 20 salt water. Funded by the manufacturer.; One small study; Source [11]
A genetic subgroup that might respond: In an analysis done after the big trial had already failed, the quarter of participants whose disease came from a fault in ordinary chromosomal DNA rather than in the power plants' own DNA walked 25.2 metres further against 0.3 metres on a dummy injection (p = 0.03). Within that group, the few with a particular eye-muscle problem walked 37.3 metres further against 8.0 metres worse (p = 0.0024). These are searches through a negative trial, run after it was known to have failed and protected by nothing; the authors present them as a reason to design the next trial, not as a result.; Subgroups of the 218 adults in the failed trial: 74 per cent had faults in the power plants' own DNA and the rest in chromosomal DNA. The chromosomal-DNA group numbered 59; the eye-muscle subgroup within it, 18 on the drug and 14 on a dummy injection.; One small study; Source [23]

What can go wrong

6 effects, 2 serious

Essentially everyone reacts where the needle goes in: all 12 people in the Barth trial had a reaction on elamipretide against 8 of 12 on the dummy injection, with redness in 12 against 3, and it is a daily injection meant to continue indefinitely. Serious allergic reactions have happened, starting anywhere from minutes to months after the first dose, and are the label's only outright ban — anyone who has had one must never be given it again. Eosinophils, a white blood cell linked to allergy, rise often in people treated for 30 days or more, peaking around day 90 and settling over the following 6 to 12 months. The vials contain benzyl alcohol, which has caused fatal illness in premature newborns given it into a vein; the product is not approved for newborns and not approved for intravenous use. No cancer study had ever been done in any species at the time of approval, and the regulator required two, reporting in 2026 and 2030. The longest anyone has taken it under study is 192 weeks, and that was three people. The amount is halved in severe kidney impairment, and for anyone on dialysis the label says there is not enough information to recommend one at all. There is no human data for pregnancy or breastfeeding, because Barth syndrome almost only affects males.

Serious allergic reactionsSerious: Rash, raised bumpy patches, eczema-like skin and coughing. The label says they can start within minutes of a dose or only after months of treatment, tells doctors to stop the drug and treat the reaction as an emergency, and says anyone who has had a serious one must never be given it again. A serious allergy to the drug or to anything in the vial is the only thing the label forbids outright.; No rate has been published. The label states these have happened, including reactions needing emergency treatment, and in the twelve-person Barth programme two people stopped the drug because of hives and a drug rash.; Source [01]Source [04]
Harm to a newborn from the preservativeSerious: Each millilitre of the liquid contains 20 milligrams of benzyl alcohol as a preservative. In very small or very premature babies given benzyl alcohol into a vein, that preservative has caused a fatal illness with acid build-up, brain damage and gasping breathing. The medicine is not approved for newborns and not approved to be given into a vein at all.; Not measured for this product, because it has never been given to newborns. The warning comes from what benzyl alcohol has done in other medicines.; Source [01]
Reactions where the needle goes in: Redness, hardening, itching, pain, bruising and hives at the injection site. It is the most common thing that happens on this medicine by a wide margin, and it happens with a daily injection that is meant to continue indefinitely. The label tells people to rotate the site around the belly or outer thigh and to keep away from scars and stretch marks, and says the reactions can be treated with antihistamines or a steroid cream.; All 12 of 12 people in the trial, against 8 of 12 on the dummy injection. Redness in all 12, against 3 on the dummy injection.; Source [01]
A rise in one type of white blood cell: Eosinophils are the white cells that go up in allergy. They drifted back to normal after six to twelve months of continued treatment, or after stopping. Nobody had symptoms from it and no other blood test moved with it.; Frequently, in studies lasting 30 days or more. Peaked around 90 days after the first dose, at an average rise of about 0.5 to 0.6 thousand cells per microlitre. No rate against a dummy injection has been published.; Source [01]
Anything to do with cancer: The regulator required two of them as a condition of approval — a 26-week study in mice with reports due in February 2026, and a two-year study in rats with reports due in January 2030. The drug did not damage DNA in the three standard laboratory tests. That is a different and much weaker thing than knowing what years of daily injections do.; Not measured. At the point of approval no cancer study of any length had been done in animals, and none has been done in people.; Source [01]Source [02]
Anything that only appears after a few years: Eight people reached week 168 of the open extension. Nobody died in it and the three serious events recorded were judged unrelated. That is the entire long-term safety record of the medicine, and it comes from a group small enough to fit around a table.; Not measured, in the sense that matters. The longest anyone has taken it under study is 192 weeks, and that was three people.; Source [01]Source [04]

Who it is known to be dangerous for

The label forbids it to one group only: anyone who has had a serious allergic reaction to elamipretide or to anything in the vial, and it says such a person must never be given it again. Beyond that outright ban, several groups are ruled out because nobody knows. It is not approved for newborns, because the preservative it contains has killed premature babies when given into a vein, and it is not approved to be given into a vein at all. It has not been established in children weighing under 30 kilograms. Nobody aged 65 or over was enrolled in the Barth trials. In severe kidney trouble the amount is halved, and in anyone on dialysis the label says there is simply not enough information to recommend an amount at all. There is no information on use in pregnancy or breastfeeding for a plain reason: Barth syndrome is passed on in a way that almost only affects males, so no woman has ever taken this drug for it. And the medicine blocks one transporter in the kidney, so the regulator has required a study of what happens when it is taken alongside metformin, a common diabetes tablet that uses that transporter — a study that had not been done when the drug was approved.

The amounts the studies used

6 amounts

These are the amounts the studies below gave their participants, and they are here as facts about those studies. They are not a recommendation, not a starting point and not a range to pick from. What a person should take, if anything, is a question for a doctor who knows them.

The approved product, Forzinity, for improving muscle strength in Barth syndrome in people weighing at least 30 kg: 40 mg injected under the skin of the belly or outer thigh, once a day at the same time each day. Halved to 20 mg in adults whose kidney filtering has fallen below 30 mL per minute and who are not on dialysis.; Indefinitely. The label sets no stopping point and the effects in the trial did not outlast treatment.; Source [01]
TAZPOWER — the Barth syndrome trial the approval came from, against a dummy injection, followed by an open extension: 40 mg injected under the skin once a day.; Two 12-week periods with a 4-week gap between, in a random order, followed by up to 192 weeks in which everyone knew they were on the drug.; Source [08]Source [24]
MMPOWER-3 — the 218-person trial in primary mitochondrial myopathy that missed both of its main measures: 40 mg injected under the skin once a day, against a dummy injection.; 24 weeks, followed by an open extension.; Source [06]
ReCLAIM-2 — dry age-related macular degeneration, against a dummy injection: 40 mg injected under the skin once a day.; 48 weeks, with 4 weeks of follow-up.; Source [09]
PROGRESS-HF — heart failure with a weak pump, against a dummy injection: 4 mg or 40 mg injected under the skin once a day, in separate groups.; 28 days.; Source [10]
Roshanravan and colleagues 2021 — a single dose in healthy older adults with poorly functioning muscle power plants, against salt water: 0.25 mg per kilogram of body weight per hour, given into a vein. This is the only published human study using a drip rather than an injection under the skin.; One two-hour infusion, with measurements straight afterwards and at day 7.; Source [11]

What people report

What follows is what people say online. It is not evidence, it is not graded, and it is not checked by anyone. People who had a bad time and people who are selling something both post more than people for whom nothing happened. It is here because you would go and read it anyway, and knowing who is talking is better than not.

Patients and families told the regulator it changed their lives, and the trial had not shown it

Fifteen people spoke at the public hearing before the FDA's advisory committee on 10 October 2024. One man who had been in the trial since 2017 described being unable to walk a quarter of a mile as a young adult and now exercising four times a week for 90 minutes, and said that during the wash-out period between the two halves of the trial he went completely back to being tired, weak and drained. A father of two sons the same age, both with the disease, described their heart scans staying stable through the growth spurt that usually makes them worse. The committee then split down the middle over what to do with this: members who voted yes explicitly named the anecdotal evidence from that hearing as a reason, and members who voted no wrote that one cannot reliably rely on anecdotal data.

Read in The FDA's own transcript and summary minutes of the Cardiovascular and Renal Drugs Advisory Committee meeting of 10 October 2024, both published in full. The vote was 10 in favour and 6 against.

What the published studies say

In the randomised half of the very trial those speakers were in, nothing separated: 443.1 metres walked against 443.9 on a dummy injection, and knee strength up 4.7 newtons against the dummy injection's 6.2.

It is bought online as an anti-ageing peptide by people who do not have Barth syndrome

SS-31 circulates in the direct-to-consumer peptide market as a mitochondrial or longevity compound, alongside things like MOTS-c and BPC-157. A 2026 review in Sports Medicine names it among the peptides sold this way and describes the parallel grey market they move through as operating largely outside regulatory oversight.

Read in Named in the 2026 Sports Medicine review of approved and unapproved peptides marketed direct to patients. No individual forum thread is cited here: Reddit refused every attempt to fetch it and no other venue could be opened and checked, so no post count or user figure is printed.

What the published studies say

The only thing ever measured in ordinary older adults is a rise in one muscle's energy production after a single drip, which was gone within a week and came with no change in how long that muscle could keep working.

Where to read it yourself

Barth Syndrome Foundation
Patient organisation
The patient organisation for Barth syndrome families. Its advocacy pages carry a dated public timeline of the whole regulatory fight, including the advisory committee vote and the FDA's refusal in May 2025 before the approval in September.
It campaigned openly and hard for this drug to be approved, which is its job and is not hidden. It paid the travel costs of several of the people who spoke at the FDA hearing, and each of them said so on the record. It publishes no industry funding disclosure on the pages read here.
United Mitochondrial Disease Foundation
Patient organisation
A patient organisation for mitochondrial diseases more broadly. Its page on the approved product covers who it is for, how it is taken and how to get hold of it, and records that it became commercially available on 4 December 2025 through a single specialty pharmacy.
It is an advocacy organisation for a group of diseases with almost no treatments, and it describes the drug in the language of an arrival rather than of a contested approval. Its account of the evidence is much shorter than the regulator's own, and it discloses no industry funding on this page.
FDA public docket FDA-2024-N-3969
Public comments sent to a regulator
The public comment file the FDA opened for the October 2024 advisory committee meeting on this exact application, alongside the full published meeting transcript. It is where members of the public sent written views on whether the drug should be approved.
Comment files fill up with people who have a stake — patients, families and the organisations that campaign for them — and almost nobody writes in to say a drug did nothing for them. The comment count could not be verified from here, because regulations.gov refused the request, so no number is printed. The meeting transcript, by contrast, opened without difficulty and is quoted above.
FDA Adverse Event Reporting System, via the openFDA query interface
Official side-effect reports
The US regulator's searchable file of side-effect reports sent in by patients, doctors and manufacturers. The link runs a live count of what has been reported alongside the brand name Forzinity.
Searched on 3 August 2026, it returned no matches at all — for the brand name or for elamipretide. That is not evidence of safety. It is what a medicine looks like when it has been on sale since December 2025 for a disease with roughly 130 people in the country. As reports accumulate the query will start returning results, and nothing in this file should be read as a statement about what they will show.
r/Peptides
Reddit community
The largest general community for people buying and injecting peptides outside a pharmacy, and one of the places SS-31 is discussed as a mitochondrial or longevity compound.
Sellers and resellers post there. Nothing is checked, nobody knows what is in the vials being discussed, and people for whom nothing happened rarely write about it. It is listed so a reader can go and weigh it directly. No claim on this page is drawn from it — every attempt to fetch it was refused, so nothing in it was actually read.

What nobody has measured

17 unknowns

Whether the leg strength the approval rests on corresponds to anything a patient can feel — the regulator called it an intermediate measure and required a controlled trial, due to report in 2030, to find out.
Whether it does anything at all in Barth syndrome that a dummy injection does not: the randomised comparison missed both of its main measures and every one of its secondary ones.
What happened in NuPOWER, the 102-person trial built on the one hopeful subgroup — it finished in December 2024 and no result has been posted or published.
Whether the subgroup findings from the failed 218-person trial are real: they were found by searching a negative trial, and the largest of them did not reach significance.
Whether it raises the risk of cancer — no cancer study had been done in any species at the time of approval, and the two the regulator ordered report in 2026 and 2030.
What it does over more than 192 weeks, and in more than the eight people who reached week 168.
What it does in children weighing under 30 kilograms — never established, which for an infantile-onset disease is a large gap.
What it does in anyone aged 65 or over: nobody that old was enrolled in the Barth trials.
What amount is right for anyone on dialysis — the label says there is not enough information to say.
What happens when it is taken alongside metformin, a common diabetes tablet that uses a kidney transporter this drug blocks; the study was ordered as a condition of approval and had not been done.
Whether it does anything for the eye: the 176-person trial missed both of its main measures, and the 313-person follow-up does not report before September 2027.
Whether it helps the kidney in a person: the only human study was a 14-person pilot in which, by the regulator's account, the treated group was never compared with the comparison group.
Whether it adds strength, muscle or endurance to anyone without a mitochondrial disease — never measured, at any amount.
Whether it slows ageing in any sense: the single-dose energy rise in older muscle vanished within a week and came with no change in fatigue.
What years of daily injections do to the immune system, given that a white cell linked to allergy rises often in people treated for more than a month.
What is in vials sold online as SS-31, which is an entirely different question from what is in the approved product.
What it does in women, in pregnancy or in breastfeeding — Barth syndrome almost only affects males, so no woman has taken it for the approved use and the label has no human data at all.

Questions people ask

10 questions

Does SS-31 work?: For most of what it has been tested on, no. A trial in 218 adults with an inherited muscle disease found people walked 3.2 metres less far than on a dummy injection; trials in heart failure, in heart attack and in 176 people with an eye disease all missed what they set out to change. The one place it is approved is Barth syndrome, an ultra-rare genetic condition, and even there the randomised part of the trial showed nothing — the leg strength the approval is based on only rose afterwards, when everyone knew they were taking it and there was nobody left to compare against.; Source [01]Source [04]Source [06]
Is SS-31 FDA approved?: Yes, since 19 September 2025, under the brand name Forzinity and for one condition only: improving muscle strength in adults and children with Barth syndrome who weigh at least 30 kilograms. It was approved on the accelerated pathway, which means the regulator accepted a stand-in measurement — knee strength — rather than proof that people are better off, and required the company to run a proper controlled trial afterwards to check. That trial began recruiting in 2026 and is not due to finish until 2029. It is approved for nothing else, anywhere.; Source [02]Source [03]Source [25]
Is SS-31 approved in Europe?: No. There is no European marketing authorisation for elamipretide and no European public assessment report, which means no licensed product exists to prescribe or buy in the EU. What does exist is orphan status — a designation the European Medicines Agency granted for Barth syndrome on 20 May 2021 and for a mitochondrial DNA depletion disease on 16 May 2022. Orphan status is regulatory support for developing a medicine; the agency states plainly that it does not mean the medicine is available or authorised.; Source [13]Source [14]
What are the side effects of SS-31?: The one everybody gets is a reaction where the needle goes in — redness, hardening, itching, pain, bruising or hives. All twelve people in the trial had one on the drug, against eight of twelve on a dummy injection. A type of white blood cell linked to allergy rises often in people treated for more than a month and settles again over six to twelve months. The serious one is a genuine allergic reaction, which can start minutes after a dose or months in, and which means never taking it again. Nobody has ever run a cancer study of it in animals or in people; the regulator ordered two in animals as a condition of approval, with the longer one not reporting until 2030.; Source [01]Source [02]
SS-31 vs MOTS-c — what is the difference?: Both are short peptides sold online as mitochondrial or anti-ageing compounds, and their evidence could hardly be further apart. SS-31 has been through more than a dozen registered human trials including two of phase 3 size, and is an approved medicine in the United States for one ultra-rare disease — while failing its biggest trials. MOTS-c has no approval anywhere and is on the World Anti-Doping Agency's prohibited list by name, as a metabolic modulator. What they share is that neither has ever been shown to slow ageing or add strength in a healthy person.; Source [01]Source [15]Source [26]
Is SS-31 the same as elamipretide?: Yes. SS-31 is the laboratory code from the group that invented it, elamipretide is the official drug name, and Forzinity is the brand it is sold under in the United States. It has also been called MTP-131 and Bendavia in older heart trials. All four names describe the same four-amino-acid molecule.; Source [01]Source [19]Source [27]
Can you buy SS-31?: In the United States, with a prescription, as Forzinity — and only if you have genetically confirmed Barth syndrome and weigh at least 30 kilograms. It has been on sale there since 4 December 2025 through a single specialty pharmacy. In the EU there is no licensed product at all. Vials sold online as SS-31 for research are outside every part of that: nobody has checked what is in them, and a 2026 review in Sports Medicine describes exactly this grey market operating without regulatory oversight. This register does not link sellers and does not tell anyone how to use anything.; Source [13]Source [26]Source [28]
Is SS-31 banned in sport?: Not by name, and as of the 2026 list not at all, as far as can be established from the list itself. Elamipretide appears nowhere in the World Anti-Doping Agency's 2026 Prohibited List. Until September 2025 it would have been caught by the list's catch-all for substances with no approval from any health regulator anywhere; the US approval removed it from that category three months before the 2026 list took effect. An athlete should still check with their own anti-doping body rather than rely on this reading.; Source [02]Source [15]
Does SS-31 do anything for ageing?: One study has looked, and it is very thin. Thirty-nine healthy people aged 60 to 85 got a single two-hour drip; straight afterwards, one hand muscle was making energy 27 per cent faster than before, against 12 per cent in the group given salt water. A week later the difference had disappeared, and how long that muscle could keep contracting had not changed at all. The study was funded by the manufacturer. A 30-person open pilot in older adults with no comparison group was still running in 2026. Nothing has been measured about lifespan, frailty or strength in a healthy person.; Source [11]Source [29]
Why was SS-31 approved if its big trial failed?: Because Barth syndrome is a different question from the diseases the big trials were run in, and because it affects about 130 people in the United States, so a large trial is not really possible. The FDA refused to even file the application in 2021, on the grounds that no adequate controlled trial supported it, and the company resubmitted without running the new trial the agency had asked for. An expert committee voted 10 to 6 that the drug was effective, with several of the yes votes saying openly that they were using regulatory flexibility and that the uncertainty was large. The FDA then declined once, in May 2025, before approving in September on the accelerated pathway with a confirmatory trial required.; Source [02]Source [04]Source [05]

Sources

29 sources

Growth & muscle · Ageing & lifespan

14 peptides · strongest evidence first