SS-31 Is an Approved Drug Now. Just Not for What It Is Sold For.

SS-31 has a following in longevity circles as a peptide that protects mitochondria, the parts of your cells that produce energy. It is sold online as a research chemical and discussed in forums as a way to slow cellular aging.

It is also, since September 19, 2025, an FDA approved medicine.

Both of those things are true at once, and this month they collided. The FDA issued warning letters to five online sellers whose websites listed products including elamipretide, the drug name for SS-31, alongside retatrutide, semaglutide, tirzepatide, and tesamorelin. All were cited for selling unapproved drugs.

So how can an approved drug be an unapproved drug?

What was actually approved

The FDA granted accelerated approval to elamipretide, sold as Forzinity, to improve muscle strength in people with Barth syndrome who weigh at least 30 kg.

Barth syndrome is an ultra-rare inherited disease, affecting roughly one in every 300,000 to 400,000 people, almost all of them male. It damages mitochondria and causes heart problems, muscle weakness, delayed growth, chronic fatigue, and low white blood cell counts. Before this approval there was no treatment for it at all.

Elamipretide works by binding cardiolipin, a fat molecule in the inner membrane of mitochondria that holds the energy-producing machinery in place. Forzinity was the first approved treatment for Barth syndrome and the first approved drug designed to act directly on mitochondria. That is a genuine scientific milestone.

What accelerated approval means

The word "accelerated" matters here, and it is easy to skip past.

Normal approval requires evidence that a drug improves how patients feel, function, or survive. Accelerated approval, used for serious diseases with no alternatives, allows approval based on an intermediate measure that is reasonably likely to predict that kind of benefit.

For elamipretide, that measure was knee extensor muscle strength, from a small randomized crossover trial in about a dozen patients. Stronger leg muscles are a reasonable signal in a disease defined by muscle weakness. But it is a signal, not proof that patients do better over time.

That is why the approval came with a condition. Continued approval may depend on a confirmatory trial verifying clinical benefit. That trial, called 4TAZPower, dosed its first patient on July 8, 2026. It is randomized, double blind, placebo controlled, and runs for 72 weeks. If it fails to confirm benefit, the approval can be withdrawn.

Why the online version is still illegal

An approval is not a blessing on a molecule. It covers a specific product: made by a specific manufacturer under controlled conditions, at a specific dose, for a specific group of patients, under a prescription.

A vial of research-grade SS-31 bought online is none of those things. It is not Forzinity, any more than the counterfeit retatrutide that testing found was almost never what its label said is the drug Lilly ran through Phase 3 trials. The name is shared. The manufacturing, quality control, and accountability are not.

The longevity gap

Here is the part that matters most for the people actually buying it.

The approval is evidence about one thing: muscle strength in a rare genetic disease where mitochondria are broken from birth. It says nothing about healthy people whose mitochondria work normally, who take SS-31 hoping to feel more energetic or age more slowly.

We have seen this pattern before with setmelanotide, an approved peptide that works dramatically in people with a specific broken appetite pathway and would do little for anyone else. A drug fixing a defect is not evidence that the same drug improves a system with no defect.

The longevity case for SS-31 still rests where it did before the approval: on animal studies and on sound but general reasoning about mitochondria and aging, much like the other mitochondrial peptides, MOTS-c and humanin.

A correction on our own page

In preparing this piece we found that our SS-31 page still described it as experimental and did not mention the 2025 approval. That was out of date, and we have updated it to reflect the approval, what it covers, and what it does not.

Sources: Stealth BioTherapeutics announcement of Forzinity accelerated approval, first patient dosed in the 4TAZPower confirmatory study, and Partnership for Safe Medicines on the September warning letters.