What it is
Follistatin is a glycoprotein the body makes — 288 or 315 amino acids in its circulating forms. It is not a short peptide, which matters for everything that follows. It was first identified in ovarian follicular fluid, and the name has stuck long past the point where it describes what the protein does.
Its established job is to bind and neutralise members of the TGF-beta family. One of them is myostatin.
Why that makes it interesting
Myostatin is the body's brake on muscle growth. Animals and, rarely, people with non-functioning myostatin build conspicuously more muscle. Follistatin binds myostatin and takes it out of circulation.
So the reasoning is short and each step is real: myostatin limits muscle; follistatin neutralises myostatin; therefore more follistatin should mean less limiting. This is one of the cleanest mechanistic stories in the whole peptide catalogue, and it is why the compound sells.
The step that does not follow is the last one — that injecting the protein into a person produces that result.
The number that looks like evidence and is not
PubMed indexes 3,232 follistatin records, 1,727 of them tagged human (E-utilities, 2026-09-08). That looks like a serious human evidence base.
Nearly all of it measures the body's own follistatin rather than giving any. Researchers track circulating follistatin as a marker: how it moves after exercise, in metabolic disease, in pregnancy, in various cancers. That is genuine human research about the protein. It says nothing about administering it, and the two get conflated constantly because the same word sits in both.
The one study that administers it
ClinicalTrials.gov returns 15 studies. Most are observational, or measure follistatin-like protein levels as an outcome inside a study of something else.
One administers follistatin: NCT07443826, recruiting as of 2026-09-08, 12 planned participants, sponsored by Unlimited Biotechnology LLC. Its intervention, as the registry describes it, is a one-time intramuscular administration of an adeno-associated virus, serotype 9, vector encoding human follistatin, combined with an intramuscular VEGF plasmid.
That is gene therapy. It is not an injection of follistatin.
| Gene therapy (what is being trialled) | Injecting the protein (what is sold) | |
|---|---|---|
| What is delivered | Instructions, in a viral vector | A quantity of protein |
| What happens next | The person's own cells produce the protein | The injected protein is cleared |
| Duration | Potentially long-lasting from one administration | Limited by clearance; repeated administration needed |
| Human evidence | One recruiting study, 12 participants, no results | None that has reported |
Evidence for the first is not evidence for the second. They differ in pharmacology, duration, risk profile and regulatory path.
About the vial
Vials in this market are usually labelled Follistatin-344 or Follistatin-315. Those numbers refer to precursor and circulating forms of the protein — a claim about molecular identity, not a dose and not an effect.
Two problems sit on top of each other. There is no human trial of injected follistatin to supply a reference for what any quantity would do. And a 300-plus-residue glycoprotein is a substantially harder thing to synthesise, fold correctly and verify than the short peptides most of this market handles, so the identity claim on the label is itself doing more work than usual.
Where it stands
The biology is real and well characterised. The human literature is large and is about measurement, not administration. The only registered study that gives anyone follistatin gives them a gene instead of the protein, has twelve planned participants, and has not reported. For the product actually sold — an injectable protein — the number of completed human trials is zero.
Related entries in this library: IGF-1 LR3 is the other muscle-growth compound sold on a mechanism that is real in principle, and it raises the same question about what a vial actually contains. The drugs actually being tested in people on this mechanism are antibodies: bimagrumab blocks the receptor myostatin signals through, and trevogrumab binds myostatin itself.
Last checked
2026-09-08. The ClinicalTrials.gov record for NCT07443826 was read through the registry API on that date; the PubMed counts were run the same day.