Follistatin 344 (FST-344 splice variant)
Myostatin-binding protein splice variant
At a glance
What it is: Myostatin-binding protein splice variant.
Primary research applications:
- Myostatin blockade for muscle growth (bodybuilding claims)
- Research into muscular dystrophies
Editorial summary: Follistatin is a genuine myostatin-binding protein with dramatic muscle-building effects in animal models. The commercial peptide 'Follistatin 344' sold in grey markets has no human clinical evidence for efficacy or safety.
What is Follistatin 344?
Follistatin is a naturally occurring protein that binds and inhibits myostatin (GDF-8) — the negative regulator of muscle growth. The 344 splice variant is one of two main circulating isoforms. Gene therapy approaches using follistatin have been tested in muscular dystrophy.[1]
Mechanism of action
By binding myostatin, follistatin releases the natural brake on muscle growth, enabling hypertrophy beyond normal limits. It also binds activin and other TGF-β family members.
What the research shows
The peer-reviewed literature on Follistatin 344 is summarized below across two tiers: human research (the highest standard), and preclinical / emerging research (animal models and early-stage human work).
Claims and the evidence behind them
This table summarizes commonly discussed claims and how the published evidence weighs in. The aim is clarity — supported claims, claims that look promising but need more data, and claims that outrun the science.
| Claim | What the evidence shows | Verdict |
|---|---|---|
| Produces extreme muscle hypertrophy | Animal and gene therapy contexts only | Preliminary |
| Is safe when injected | No human safety data for injectable peptide form | Unsupported |
Reported user experiences
How the research describes administration
Grey-market injectable; no validated clinical protocol.
Editorial note
Administration details above describe how the peptide is given in published studies. We summarize this for educational completeness — these descriptions are not protocols, dosing recommendations, or instructions for personal use. Decisions about treatment require an appropriately licensed clinician.
Safety considerations and open questions
The takeaway
Interesting biology, aggressive marketing, and essentially no human efficacy or safety data for the commercially sold peptide. Treat with heavy skepticism.
Frequently asked questions
Does follistatin really block myostatin?
Yes — that's an established biological function. Whether injected 'follistatin 344' from grey-market sources produces meaningful systemic myostatin blockade in humans is a different question with no data.
Is follistatin safe?
Human safety data for injectable peptide forms is absent. Animal and gene-therapy studies raise some questions about cardiac and reproductive effects.
References
- Lee SJ, McPherron AC. Regulation of myostatin activity and muscle growth. Proc Natl Acad Sci USA. 2001;98(16):9306-11. https://pubmed.ncbi.nlm.nih.gov/11459935/
- Mendell JR, Sahenk Z, Malik V, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy. Mol Ther. 2015;23(1):192-201. https://pubmed.ncbi.nlm.nih.gov/25322757/