Performance & GH axis
Follistatin 315
FST-315, follistatin
Follistatin 315 is the predominant circulating isoform of follistatin, a myostatin- and activin-binding protein. It is sold as a research peptide alongside Follistatin 344, and is distinct from it.
Also known as: FST-315, FST315, follistatin-315
- Status
- Follistatin 315 is a research compound and not approved by the FDA for human use.
- Evidence
- Preclinical. Evidence comes from animal or lab studies; effects in people are not established.
- Half-life
- Very short — on the order of minutes to a few hours.
- How it's taken
- Subcutaneous or intramuscular injection in non-clinical use
- Mechanism
- Anabolic (IGF-1 / myostatin)
- Pathways
- Myostatin
How Follistatin 315 works
Follistatin binds and neutralises myostatin, activin A and several other TGF-beta family ligands, removing their restraint on muscle growth. FST-315 is the longer circulating isoform with lower heparin-binding affinity than FST-288, so it remains in the bloodstream rather than binding tightly to cell surfaces. Follistatin 344 is a precursor that is processed to FST-315, which is why the two are related but not interchangeable.
What research has looked at
- Myostatin inhibition is a genuinely validated route to increased muscle mass in animal models, with dramatic phenotypes in myostatin-null animals and humans.
- The circulating isoform has a pharmacokinetic profile more relevant to systemic administration than the cell-surface-binding FST-288.
- Gene-therapy approaches delivering follistatin have been trialled in muscular dystrophies.
Evidence level: Preclinical. Evidence comes from animal or lab studies; effects in people are not established. These are areas studied or reported, not promised effects.
Reported side effects and risks
- No follistatin product is approved for any indication, and no controlled human trial supports its use for muscle building. No regulator has approved it, the human evidence base is limited, and material sold under this name is research chemical supply with unverified identity, purity, sterility and dose accuracy.
- Follistatin binds activins as well as myostatin, and activin signalling has broad roles in reproduction, inflammation and tumour suppression — systemic neutralisation is not a targeted intervention.
- Every myostatin-pathway drug that has reached late-stage trials has increased muscle mass without improving physical function, the pattern seen with bimagrumab and ostarine.
- Follistatin has a very short circulating half-life, making sustained suppression from intermittent injection implausible.
- Prohibited at all times under the WADA Prohibited List as a myostatin inhibitor.
Sources
- PubMed research on follistatin 315 myostatin activin binding · NIH · National Library of Medicine
- DrugBank record for follistatin · DrugBank
- Active clinical trials for follistatin · U.S. National Library of Medicine
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Follistatin 315 FAQ
What is Follistatin 315?
Follistatin 315 is the predominant circulating isoform of follistatin, a myostatin- and activin-binding protein. It is sold as a research peptide alongside Follistatin 344, and is distinct from it.
How does Follistatin 315 work?
Follistatin binds and neutralises myostatin, activin A and several other TGF-beta family ligands, removing their restraint on muscle growth. FST-315 is the longer circulating isoform with lower heparin-binding affinity than FST-288, so it remains in the bloodstream rather than binding tightly to cell surfaces. Follistatin 344 is a precursor that is processed to FST-315, which is why the two are related but not interchangeable.
Is Follistatin 315 FDA approved?
No. Follistatin 315 is a research compound and not approved by the FDA for human use. Evidence level: preclinical. Evidence comes from animal or lab studies; effects in people are not established.
What is the half-life of Follistatin 315?
Reported half-life: Very short — on the order of minutes to a few hours.
How is Follistatin 315 taken?
Subcutaneous or intramuscular injection in non-clinical use.
What side effects have been reported with Follistatin 315?
Reported in the sources: No follistatin product is approved for any indication, and no controlled human trial supports its use for muscle building. No regulator has approved it, the human evidence base is limited, and material sold under this name is research chemical supply with unverified identity, purity, sterility and dose accuracy; Follistatin binds activins as well as myostatin, and activin signalling has broad roles in reproduction, inflammation and tumour suppression — systemic neutralisation is not a targeted intervention; Every myostatin-pathway drug that has reached late-stage trials has increased muscle mass without improving physical function, the pattern seen with bimagrumab and ostarine; Follistatin has a very short circulating half-life, making sustained suppression from intermittent injection implausible; Prohibited at all times under the WADA Prohibited List as a myostatin inhibitor.
Educational summary compiled from the sources listed above. Not medical advice. Peptide Vault does not sell, source or recommend any compound. Talk to a qualified clinician before starting or changing anything.