Performance · Investigational
Follistatin-344
No lawful US pathway
01 · Overview
Follistatin-344 is an alternatively spliced isoform of follistatin, a secreted binding protein that neutralizes myostatin, activin and other TGF-beta superfamily ligands. Removing these inhibitory signals increases skeletal muscle mass, and work in mice shows the hypertrophy depends both on satellite cell proliferation and on inhibition of activin as well as myostatin (PMID 19435857).
The FS344 isoform was selected for therapeutic gene delivery because it affects skeletal muscle with only minimal effects on non-muscle cells (PMID 20368179). Pigs engineered to express human follistatin-344 in muscle showed a higher proportion of lean tissue, less body fat and myofiber hypertrophy (PMID 27787698).
02 · Research summary & key findings
In cynomolgus macaques, intramuscular delivery of an AAV1 vector carrying FS344 produced pronounced and durable increases in muscle size and strength without abnormal changes in major organs (PMID 20368179). In an open-label phase 1/2a trial, six men with Becker muscular dystrophy received intramuscular AAV1.CMV.FS344 in both quadriceps; four improved on the 6-minute walk test, two did not, muscle biopsies showed reduced fibrosis and fiber hypertrophy, and no adverse effects were reported in this very small uncontrolled study (PMID 25322757). A similar trial in six patients with sporadic inclusion body myositis reported a median annualized walking improvement compared with untreated historical comparators (PMID 28279643). Off-target concerns are not resolved: in mice, follistatin increased muscle mass but weakened bone (PMID 32071240), and black market follistatin 344 products have been found to be impure or to contain other peptides entirely (PMID 31758732).
03 · Regulatory status
Follistatin-344 is in the investigational stage. While preclinical and early-phase data exist, it has not received regulatory approval for clinical use in the United States.
No lawful pathway today
Follistatin-344 is not FDA-approved and does not currently have a lawful prescription or compounding pathway in the United States, so we do not sell it and will not book a consultation for it. That can change: in 2026 FDA began reviewing several peptides for compounding. If you are working on the goal it is studied for, a licensed clinician can tell you what is lawfully available, which may be something else.
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Follistatin-344 is an investigational compound, is not FDA-approved, and has no lawful US compounding pathway, so we do not offer it and no clinician we work with will prescribe it. Products sold online as “research chemicals” are not made or tested to the standards required of medicines. If you are working on athletic performance, a licensed clinician can tell you at a free consultation whether an FDA-approved or lawfully compounded treatment fits you, or whether nothing does.
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04 · Administration routes
- Intramuscular injection
- Gene delivery
References
- [1]Follistatin induces muscle hypertrophy through satellite cell proliferation and inhibition of both myostatin and activin Am J Physiol Endocrinol Metab, 2009. PMID 19435857
- [2]Follistatin gene delivery enhances muscle growth and strength in nonhuman primates Sci Transl Med, 2009. PMID 20368179
- [3]A phase 1/2a follistatin gene therapy trial for becker muscular dystrophy Mol Ther, 2015. PMID 25322757
- [4]The transgenic expression of human follistatin-344 increases skeletal muscle mass in pigs Transgenic Res, 2017. PMID 27787698
- [5]Follistatin Gene Therapy for Sporadic Inclusion Body Myositis Improves Functional Outcomes Mol Ther, 2017. PMID 28279643
- [6]Detection of black market follistatin 344 Drug Test Anal, 2019. PMID 31758732
- [7]GDF11 promotes osteogenesis as opposed to MSTN, and follistatin, a MSTN/GDF11 inhibitor, increases muscle mass but weakens bone Proc Natl Acad Sci U S A, 2020. PMID 32071240
Primary literature
- PubMed: "Follistatin-344"
Peer-reviewed literature indexed by the National Library of Medicine.
- ClinicalTrials.gov: "Follistatin-344"
Registered interventional and observational studies, including status and phase.
- PubChem: "Follistatin-344"
Chemical structure, molecular properties, and bioactivity data.
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