Growth hormone axis
Follistatin-344
FS-344 · Myostatin inhibitor · myostatin · inhibitor
A myostatin-blocking peptide with dramatic effects in animal studies — essentially untested in humans, with real theoretical safety questions.
Reference status
Editorial research · independent review pending · 3 claims graded
What it is
Follistatin-344 blocks myostatin, a protein that normally limits muscle growth. Animal studies (including in mice and primates) have shown striking increases in muscle mass when myostatin signalling is blocked — this is genuinely dramatic biology.
The honest caveat is that myostatin exists for a reason, and blocking it long-term in humans has not been studied in controlled trials. Related gene-therapy research into myostatin inhibition has raised safety questions that haven't been resolved for peptide-based approaches like this one.
The science, graded
What’s claimed — and how strong the evidence behind each claim actually is.
“Dramatically increases muscle mass”
Striking effects in animal models; no human trial has tested this at any dose.
Claim-level citation mapping is in progress.
“Safe to use for extended periods”
Unknown. Long-term myostatin inhibition in humans is genuinely understudied, and this claim isn't supported by data.
Claim-level citation mapping is in progress.
“Works well stacked with GH-axis peptides”
A community theory based on complementary mechanisms, not a tested combination.
Claim-level citation mapping is in progress.
Legal and regulatory context
Separate summaries for Great Britain, the United States, and the European Union. These are preliminary research summaries awaiting independent regional review; they are not legal determinations or advice.
Great Britain
Not a licensed medicine in the UK; a research chemical only, with no legal human-use supplement route.
This is preliminary regulatory research, not a reviewed legal determination or legal advice.
United States
Regional legal and regulatory review required before publication.
This is preliminary regulatory research, not a reviewed legal determination or legal advice.
- FDA's Concerns About Unapproved Drugs · U.S. Food and Drug Administration
European Union
Regional legal and regulatory review required before publication.
This is preliminary regulatory research, not a reviewed legal determination or legal advice.
- Buying medicines online · European Medicines Agency
What the community says
Discussed with a mix of fascination and caution — the animal data genuinely impresses even sceptical readers, but the total lack of human safety data is repeatedly flagged.
Where they’re talking
- r/PeptidesOne of the more debated 'is this too experimental' compounds.
- Bodybuilding forumsAnimal-study screenshots circulate often.
References
- 1.Supply unlicensed medicinal products (specials) · MHRA
- 2.FDA's Concerns About Unapproved Drugs · U.S. Food and Drug Administration
- 3.Buying medicines online · European Medicines Agency