SS-31

SS-31 is a four amino acid peptide that binds cardiolipin, a fat found only in the inner membrane of mitochondria. It is one of the few compounds designed to act on a specific structure inside the cell's power plants rather than on a receptor on its surface.

In September 2025 it became an approved medicine under the name Forzinity, which changes the conversation about it considerably.

Why people are talking about it#

The approval, and the elegance of the design. Cardiolipin exists nowhere in the cell except the inner mitochondrial membrane, so a molecule that binds it is inherently targeted: it goes where cardiolipin is and nowhere else.

The disease it was approved for makes that targeting look even better. Barth syndrome is a condition defined by broken cardiolipin handling, and this is a drug that binds cardiolipin. Drug and defect line up exactly.

What people take it for#

In medicine it has one licence, and that licence is narrow. Beyond it, the compound is sold for fatigue, exercise capacity and general mitochondrial health.

Barth syndrome#

The approved use is enhancing muscle strength in patients with Barth syndrome, an inherited disorder affecting roughly one in a million male births. The mechanism is stabilisation of cardiolipin, precisely the molecule the disease disrupts.

That match is why the approval happened, and it is also why the result is specific to it.

Fatigue and ageing#

The claim is more energy and better mitochondrial function in ordinary people, applying the same cardiolipin binding to mitochondria that are ageing rather than genetically broken.

Whether that helps depends on whether tiredness in a healthy adult is a cardiolipin problem. No trial has tested the compound for it.

What the evidence shows#

The approval is real and it is accelerated approval, which means continued approval may depend on confirmatory trials verifying clinical benefit.

The wider programme is more mixed. In primary mitochondrial myopathy, the MMPOWER-3 trial missed its primary endpoint. Trials in dry age-related macular degeneration and in heart failure produced results that have not led to approvals.

So the tally is one approval in an ultra-rare disease where the mechanism matches the defect exactly, several larger trials that did not meet their endpoints, and nothing yet in healthy people. Injection site reactions were the most common problem across the programme, sometimes marked enough to affect whether people continued.

How it is taken#

The licensed product is a daily subcutaneous injection, approved for patients weighing at least 30 kg. That daily schedule and the injection site reactions are the two practical facts about living with it.

How it compares#

Against MOTS-c and NAD+#

MOTS-c and NAD+ are also sold for mitochondrial function and are unrelated molecules. SS-31 is the only one of the three that has become an approved medicine, and its approval covers a disease neither of the others claims to treat.

Against its own wider trial programme#

The most informative comparison is internal. The same compound was taken into larger trials in more common conditions and did not meet its endpoints there, which is the best available guide to what it does outside Barth syndrome.

Common questions#

Is it approved?

Yes, in the US as Forzinity for Barth syndrome, under accelerated approval.

Does it help ordinary fatigue?

No trial has tested it for that, and the larger trials in related conditions missed their endpoints.

What is cardiolipin?

A fat found only in the inner mitochondrial membrane, which is what makes it a precise target.

Why is the approval called accelerated?

Because it was granted on the basis of an early measure, with continued approval potentially depending on confirmatory trials.