SS-31 (Elamipretide) Peptide: Status, Evidence and Sellers

SS-31 is the research name for elamipretide, a peptide of four amino acids designed to reach the inner membrane of mitochondria, the structures that make most of a cell's energy. There it binds cardiolipin, a fat that helps hold the energy-making machinery together [1]. Peptide sellers market it for energy, endurance and aging on the idea that it repairs tired mitochondria.

Unlike almost everything else on those menus, it is an FDA-approved drug. On September 19, 2025 FDA approved it as Forzinity, made by Stealth BioTherapeutics, under accelerated approval, to improve muscle strength in people with Barth syndrome who weigh at least 30 kg [2] [1]. Barth syndrome is a rare inherited disorder carried on the X chromosome, so it mainly affects boys and men; the label notes it is not likely to affect females [1].

That approval is narrow and conditional, and the trials that tested elamipretide in broader groups did not succeed [3]. It is not one of the six peptides in the October 28, 2026 HHS policy.

Cardiolipin sits in the inner mitochondrial membrane and supports the chain of proteins that turns food into usable energy. Forzinity's label describes elamipretide as a cardiolipin binder that localizes there and improves mitochondrial structure and function [1].

In healthy older adults with poorly working mitochondria, one two-hour infusion raised the muscle's peak energy output on a scanner compared with placebo, an effect that was gone a week later and did not make the muscle more resistant to fatigue [4].

The approval rests on a small, mixed record. In the randomized part of the Barth trial, 12 patients took Forzinity or placebo for 12 weeks each, and it was not better than placebo on either main goal, the six-minute walk or fatigue scores. Leg muscle strength did not improve during that phase either. It rose during the open-label extension that followed, with a median gain of 63 newtons at week 168 in the eight patients who stayed on it [1]. FDA accepted that strength gain as an intermediate endpoint, and the label says keeping the approval may hinge on a further trial that confirms a clinical benefit [1].

The largest trial, MMPOWER-3, randomized 218 adults with primary mitochondrial myopathy, a broader group of inherited mitochondrial muscle diseases, to 40 mg a day or placebo for 24 weeks. It missed both primary endpoints: the difference from placebo in six-minute walk distance was -3.2 meters (p = 0.69), and fatigue scores did not differ [3].

No trial has tested it in healthy people for energy, endurance or aging. Grade B: one narrow, accelerated approval and a set of human trials, with the larger trials negative and nothing behind the uses sellers promote. Our evidence review covers MMPOWER-3 in detail.

Per the FDA label, the dose for Barth syndrome is 40 mg injected under the skin once a day, at the same time each day, cut to 20 mg in adults with severe kidney impairment who are not on dialysis. It is not approved for intravenous use [1]. That is the only approved dose, for that disease only.

There is no approved or studied dose for general wellness. Research-chemical SS-31 sold online is not Forzinity and carries none of its manufacturing or labeling controls.

In the Barth trial, injection-site reactions were near universal: every patient on Forzinity had a local reaction and redness at the injection site, against 67% and 25% on placebo, with hardening, itching and pain also common. Eosinophils, a type of white blood cell, often rose in the first months of treatment and settled back over 6 to 12 months [1].

The label warns that the product contains benzyl alcohol and must not be used in newborns, in whom benzyl alcohol has caused fatal reactions [1]. In MMPOWER-3 elamipretide was well tolerated, with most adverse events mild to moderate [3].

Elamipretide is not named on the World Anti-Doping Agency's 2026 Prohibited List, and since September 2025 it has a US approval, so the list's S0 class for unapproved substances does not plainly reach it [5]. Athletes should still confirm with their anti-doping organization.