SS-31 Peptide Dosage: What the Trials Used

Human studies of SS-31 peptide dosage have used multiple regimens, including weight-based intravenous infusions and, in PROGRESS-HF, 4 mg or 40 mg subcutaneously once daily; several later disease trials used 40 mg daily. Those figures are clinical-trial anchors rather than a dosing protocol — they were fixed inside clinical protocols, in named diseases, with monitoring, using a manufactured drug. Outside a protocol there is no established dose for compounded SS-31, and no chart on a seller's page supplies one.

SS-31 and elamipretide are two names for the same peptide; what the molecule is and how it binds cardiolipin is covered separately. This page is about the numbers.

Where the SS-31 peptide dosage figures come from

Human dosing of this peptide was set by a drug-development program that began with an intravenous dose-escalation and then moved to fixed daily injections at more than one dose.

MMPOWER, a controlled human study that followed the 40-person healthy-adult trial NCT01115920 begun in May 2010, gave elamipretide intravenously by body weight — 0.01, 0.1 and 0.25 mg/kg per hour over two hours, in an escalating sequence, to 36 adults with primary mitochondrial myopathy. Participants on the highest rate walked a mean 64.5 m further at day 5 against 20.4 m on placebo (p = 0.053), and distance walked rose with dose across the range (p = 0.014) (Karaa et al., Neurology 2018). Several later disease trials used 40 mg a day subcutaneously, while PROGRESS-HF tested both 4 mg and 40 mg.

Two things stand out. Human elamipretide studies have used multiple regimens, including weight-based intravenous infusions and, in PROGRESS-HF, 4 mg or 40 mg subcutaneously once daily; several later disease trials used 40 mg daily.

PROGRESS-HF is the only later trial that compared two subcutaneous doses head to head, randomizing 71 people with reduced ejection fraction to placebo, 4 mg or 40 mg daily for 28 days; the imaging primary endpoint was not met at either dose (Butler et al., J Card Fail 2020). Several of these trials missed their primary endpoints. MMPOWER-3 ran 218 people for 24 weeks at 40 mg a day and produced a six-minute-walk difference of −3.2 m against placebo (p = 0.69) (Karaa et al., Neurology 2023). A dose that has been studied is not the same thing as a dose that has been shown to work.

The one labeled elamipretide dose, and what it covers

In September 2025 the FDA granted accelerated approval to elamipretide, marketed as Forzinity by Stealth BioTherapeutics — the first disease-specific treatment for Barth syndrome (Shirley, Drugs 2026). That product carries a complete dosing scheme, which is worth reading precisely because of how narrow it is.

The label covers improving muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg, at 40 mg subcutaneously once daily. For adults with severe renal impairment — an eGFR below 30 mL/min who are not on dialysis — the label specifies a reduced 20 mg daily dose; mild or moderate impairment requires no adjustment, and the label has insufficient information to recommend a regimen for children with renal impairment or adults with severe renal impairment on dialysis. It is supplied as 280 mg in 3.5 mL, a concentration of 80 mg/mL, in single-patient vials; injections go into the abdomen or outer thigh with the site rotated daily, and a missed dose is skipped rather than doubled (FORZINITY prescribing information, DailyMed).

Notice what that scheme is bounded by: one manufactured product, one ultra-rare genetic disease, one weight band, one route. It is not a general-purpose dosing table for a peptide, and it was never written as one.

SS-31 is coming soon to Promise — add me to the list. It will be prepared as a compounded medication, which is different from an FDA-approved product: the compounded formulation Promise will offer is not FDA-approved. A licensed provider may still prescribe it where they judge it appropriate — that decision is between you and your doctor.

SS-31 and MOTS-c are not interchangeable numbers

SS-31 and MOTS-c are both peptides studied for their activity at the mitochondrion, which is why they are so often discussed in the same breath. Their dose figures come from entirely separate literatures, and neither transfers to the other — MOTS-c dosing is its own question with its own evidence.

Why a seller's dosing chart is not a protocol

Vials sold without a prescription usually arrive with a chart: a milligram range, a frequency, sometimes a cycle of so many weeks on and so many off. Those numbers look like the trial numbers and are not doing the same job.

• A dose without a denominator is not information. In a trial, 40 mg a day is attached to a named population, a fixed duration, a monitoring schedule and an endpoint that either moved or did not. Lift the figure out and all four disappear.
• The vial is not the dose. For compounded SS-31 preparations supplied as powder, reconstitution volume determines how many milligrams sit in each syringe unit; Forzinity is a ready-to-use solution. Two people following the same chart with different reconstitution volumes are taking different amounts — how reconstitution works covers that arithmetic.
• Nobody is adjusting it. The approved label halves the daily dose only in adults with severe renal impairment who are not on dialysis; it has insufficient information to recommend a regimen for children with renal impairment or adults with severe renal impairment on dialysis. A chart cannot know your kidney function, your other medicines, or that the injections stopped being tolerable in week three.

What a prescriber weighs

For a compounded peptide with no established dose, the decision is mostly about whether to prescribe at all, and then about keeping the exposure conservative and observable. What tends to come up:

• Whether there is a coherent clinical reason. The human evidence sits in specific diagnoses — mitochondrial myopathy, Barth syndrome, dry AMD, heart failure — mostly with disappointing primary results. A request that resembles none of them is a harder case to make.
• Kidney function, since that is the one variable the labeled dosing scheme adjusts for.
• Other medicines and conditions, plus pregnancy or breastfeeding, which rules out essentially everything in this category.
• Injection tolerability. Injection-site reactions were the dominant adverse event at 40 mg a day in every trial: 80% of the 30 participants in the MMPOWER-2 crossover, mostly mild (Karaa et al., J Cachexia Sarcopenia Muscle 2020), and 86% of people on elamipretide versus 71% on placebo for adverse events overall in the 176-person ReCLAIM-2 trial (Ehlers et al., Ophthalmol Sci 2025). In a 19-person phase 1 study, one participant withdrew because of an intolerable injection-site reaction (Mettu et al., Ophthalmol Sci 2022).
• How long, and what would count as an answer. Published durations ran from 5 days to 48 weeks; the Barth syndrome crossover used 12-week arms (Reid Thompson et al., Genet Med 2021). An open-ended prescription with no review date is not a plan.

What to settle before the first injection

The useful conversation is not "how many milligrams". It is which problem you are hoping to affect, what a daily injection actually commits you to, what would tell you it is not working, and when you will next be reviewed. Those questions have answers. A number lifted off a chart only looks like one.

SS-31 is coming soon to Promise and is prescription-only. A licensed provider reviews every request and prescribes only where it is appropriate; not everyone qualifies, and a provider may decline. If you have not been through that before, how peptides get prescribed walks through the steps.