Follistatin 344 — commonly referred to as FST 344 in research circles — is a 344-amino acid isoform of the naturally occurring glycoprotein follistatin. It functions primarily as a myostatin inhibitor and activin antagonist, making it one of the most studied peptides for muscle growth and body composition research.
Myostatin (GDF-8) is often described as the body’s natural “brake” on muscle growth. It is a member of the TGF-β superfamily that actively suppresses muscle hypertrophy and development. Follistatin 344 works by binding directly to myostatin and related activins, neutralizing their inhibitory effects and allowing for enhanced muscle protein synthesis and hypertrophy in research models.
The peptide was first characterized in the late 1980s and has since attracted significant research interest from biogerontologists, sports scientists, and researchers studying muscle wasting disorders such as sarcopenia, cachexia, and muscular dystrophy.
Follistatin exists in multiple isoforms, with FST 344 and FST 288 being the most studied in research:
For muscle growth and body composition research, FST 344 is the preferred isoform due to its systemic activity and longer duration of action.
The primary and most studied mechanism of FST 344 is direct myostatin (GDF-8) binding and neutralization. Myostatin normally binds to activin type II receptors on muscle cells, activating a signaling cascade (SMAD 2/3 pathway) that suppresses muscle protein synthesis and promotes muscle protein degradation.
When FST 344 binds to myostatin, it prevents this receptor interaction entirely, effectively removing the myostatin-mediated growth inhibition. The result in animal models is:
Beyond myostatin, FST 344 also antagonizes activins A and B — related TGF-β family members that similarly suppress muscle growth and have roles in reproductive biology, bone metabolism, and inflammation. This broader antagonism may contribute to FST 344’s observed effects on overall anabolism and tissue remodeling in research models.
Some research suggests FST 344 may indirectly support IGF-1 signaling, a key anabolic pathway for muscle growth. By removing myostatin-mediated suppression of IGF-1 receptor sensitivity, follistatin treatment may enhance the muscle’s anabolic response to growth factors already present in the research model.
The foundational evidence for follistatin’s muscle-building potential comes from myostatin knockout (MSTN-/-) mouse studies, which showed that animals lacking myostatin developed dramatically larger muscle mass — sometimes 2-3x normal. Follistatin overexpression studies in mice produced similar results, validating the myostatin-inhibition hypothesis.
A landmark study demonstrated that transgenic mice overexpressing follistatin developed significantly greater muscle mass than controls, with effects comparable to myostatin knockout. This paper established follistatin as a viable target for muscle research and set the stage for subsequent peptide research.
Research using AAV-delivered follistatin in murine muscular dystrophy models showed significant improvements in muscle mass, strength, and functional outcomes. While gene therapy differs from peptide administration, it validated follistatin’s potential in muscle wasting disease models.
This primate study (non-human primates) demonstrated that localized follistatin delivery produced significant muscle hypertrophy without systemic off-target effects, providing important safety data for higher animal models.
Based on the available preclinical literature, FST 344 is currently studied for:
Note: The following reflects dosing used in animal and preclinical research only. FST 344 is sold for research use only and is not approved for human use.
Dosing in published research varies by animal model, route of administration, and research objective:
Based on preclinical research, FST 344 shows a generally favorable safety profile with some important considerations:
All FST 344 research should be conducted by qualified researchers in appropriate settings with appropriate monitoring protocols.
IGF-1 LR3 stimulates anabolic signaling via IGF-1 receptors. FST 344 removes myostatin’s inhibitory brake on muscle growth. These work through different pathways and may be complementary in research settings. FST 344 has the advantage of more targeted muscle effects; IGF-1 has broader tissue effects including potential growth of non-muscle tissues.
GHRP peptides (Ipamorelin, GHRP-2) stimulate GH secretion which drives IGF-1. FST 344 works independently of the GH axis. FST 344 may be particularly relevant for research in subjects where GH-axis stimulation is not the primary target.
MK-677 is a ghrelin receptor agonist that stimulates GH/IGF-1 axis. FST 344 directly inhibits myostatin. Both support muscle growth through distinct mechanisms; FST 344 is more specific to myostatin biology.
For research use, FST 344 is typically lyophilized (freeze-dried) and requires reconstitution:
Research-grade FST 344 is available from select USA-based peptide suppliers. When sourcing follistatin for research:
PeptidesForSale.us stocks Follistatin 344 1mg — USA-manufactured, 99%+ purity, third-party CoA verified, fast domestic shipping.
In animal model research, measurable muscle hypertrophy effects have been observed as early as 2-4 weeks with continued progression through 8-12 weeks of treatment. Timeline varies significantly based on animal model, dose, route of administration, and concurrent protocols.
Research protocols have explored FST 344 in combination with IGF-1, BPC-157, and GH-axis peptides. These combinations target muscle growth through multiple pathways and are a common focus in body composition research.
FST 344 is a research peptide not currently on standard athletic drug testing panels, but this is outside the scope of our research focus. All products are sold for laboratory research use only.
FST 344 is the circulating systemic isoform; FST 288 is tissue-bound with localized effects. For muscle growth research, FST 344 is the preferred form. For reproductive or localized tissue research, FST 288 may be more appropriate.
FST 344 (Follistatin 344) is one of the most compelling peptides for muscle biology research, offering a direct and potent mechanism for myostatin inhibition. With a growing body of evidence from mouse, primate, and early human studies — and search interest trending upward 53% month-over-month in 2026 — FST 344 is rapidly becoming a leading focus in performance and muscle wasting research.
For researchers studying muscle hypertrophy, sarcopenia, muscular dystrophy, or body composition, FST 344 provides a well-characterized, mechanistically distinct research tool backed by two decades of peer-reviewed science.
Disclaimer: This article is for educational and informational purposes only. FST 344 / Follistatin 344 is sold for research use only and is not intended for human consumption, medical diagnosis, or treatment. All research must be conducted by qualified professionals in appropriate laboratory settings in compliance with local regulations.
