Summary
Follistatin-344 is a recombinant (lab-produced) version of the full length form of follistatin, a natural protein that binds myostatin and activin and so removes the main brake on skeletal muscle growth. Transgenic mice (bred to overproduce follistatin) roughly doubled to tripled muscle mass, and a single gene therapy injection (which delivers the follistatin gene so the body makes the protein) increased muscle size and strength in macaques, but the only human data come from small open label gene therapy trials (AAV1-FS344, with no placebo group) in muscular dystrophy and inclusion body myositis, both muscle wasting diseases, not from injecting the peptide. Injected follistatin-344 has no published human trial, is not FDA approved, is not on any FDA compounding list, and is prohibited at all times by WADA.
What is Follistatin-344?
Follistatin-344 is a recombinant form of the 344 amino acid precursor isoform of human follistatin, a secreted glycoprotein that binds and neutralizes myostatin, activins, and related TGF-beta family ligands. It is also known as FST-344, FS344, Follistatin 344, FST, Activin binding protein, AAV1-FS344 (gene therapy form).
How does it work?
Follistatin binds myostatin (GDF-8) and activin A and B with high affinity and blocks them from activating the activin type II receptors (ActRIIB and ActRIIA) on muscle cells. Loss of that signal reduces SMAD2/3 activity, releases satellite cells and protein synthesis from myostatin restraint, and produces both fiber hypertrophy and, during development, hyperplasia. The 344 isoform is the secreted precursor that is processed to the 315 (circulating) and 288 (tissue bound) forms; the 315 form is the one used in the AAV gene therapy trials because it binds heparan sulfate less and stays in the circulation. Follistatin also binds bone morphogenetic proteins and activins involved in reproduction and inflammation, which is the basis for concern about off target effects.
| Cluster | Tissue repair and healing |
|---|---|
| Routes | Subcutaneous or intramuscular injection (as sold, no human data); Intramuscular AAV1 gene therapy (clinical trials only); Transgenic overexpression and intramuscular viral vector (animal studies) |
| Conditions studied | Muscle recovery and injury; Muscle wasting and sarcopenia |
| Record | v2, draft, verified Sep 22, 2026 |
What does the evidence say about Follistatin-344?
Strong animal evidence that raising follistatin increases muscle mass: transgenic mice gained 194% to 327% in individual muscle weights, and a single intramuscular AAV1 gene therapy injection in cynomolgus macaques increased quadriceps size and strength for at least 15 months without measurable systemic toxicity. Human evidence is limited to two open label phase 1/2a gene therapy trials of 6 patients each (Becker muscular dystrophy and sporadic inclusion body myositis) that reported improved 6 minute walk distance without a placebo group. No published trial of injected recombinant follistatin-344 in humans was identified, so the evidence grade for the peptide as sold is animal-only. The human gene therapy trials used AAV1-FS344, not the injected peptide as sold; they are listed but do not raise the grade.
| Evidence type | Indexed studies | Participants (human) |
|---|---|---|
| Human randomized trials | 0 | n/a |
| Human observational studies | 2 | 12 |
| Animal studies | 2 | n/a |
| All indexed studies | 4 | 12 |
Human evidence
No indexed human trial of injected follistatin-344 peptide identified. The human data are for AAV1-FS344 gene therapy delivered into the quadriceps: in Becker muscular dystrophy (n = 6, 2015) 4 of 6 patients improved 6 minute walk distance by 58 to 125 meters over 1 year with no serious adverse events; in sporadic inclusion body myositis (n = 6, 2017) treated patients improved 6 minute walk distance by a mean of 56 meters at 1 year while untreated comparators declined. Both trials were open label, unblinded, and too small to establish efficacy; the therapy has not advanced to approval.
Animal evidence
Lee and McPherron (2001) showed that transgenic mice overexpressing follistatin had muscle weights 194% to 327% above wild type, exceeding the gain seen in myostatin knockout mice, which implicated additional ligands beyond myostatin. Kota et al. (2009) gave a single bilateral quadriceps injection of AAV1-FS344 to cynomolgus macaques and measured increased muscle circumference, fiber size, and strength persisting 15 months, with normal reproductive hormones and organ histology. Rodent models of muscular dystrophy and cachexia treated with follistatin gene delivery or recombinant follistatin also show increased muscle mass and strength.
Key studies
| Study | Design and population | Outcome | Grade |
|---|---|---|---|
| Regulation of myostatin activity and muscle growth2001 PMID 11459935 | Transgenic mouse studyMice overexpressing follistatin, myostatin propeptide, or dominant negative ActRIIB in skeletal muscle | Follistatin transgenic mice had individual muscle weights 194% to 327% above wild type, exceeding myostatin knockout, implying follistatin blocks additional growth inhibiting ligands | Evidence: Animal-only evidence |
| Follistatin gene delivery enhances muscle growth and strength in nonhuman primates2009 PMID 20368179 | Nonhuman primate gene therapy study with 15 month follow upCynomolgus macaques given bilateral quadriceps injections of AAV1-FS344 | Increased muscle size, fiber diameter, and strength maintained for 15 months with no change in reproductive hormones or organ histology | Evidence: Animal-only evidence |
| A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy2015 PMID 25322757 | Open label, dose escalation phase 1/2a gene therapy trial, 1 year follow upn = 6 Ambulatory adult men with Becker muscular dystrophy | 4 of 6 patients improved 6 minute walk distance by 58 to 125 meters; no serious adverse events; no placebo group | Evidence: Human observational evidence |
| Follistatin gene therapy for sporadic inclusion body myositis improves functional outcomes2017 PMID 28279643 | Open label phase 1/2a gene therapy trial with untreated comparator group, 1 year follow upn = 6 Adults with sporadic inclusion body myositis | Treated patients improved 6 minute walk distance by a mean 56 meters at 1 year while untreated comparators declined; unblinded, small sample | Evidence: Human observational evidence |
Conditions studied
| Condition | Grade | Note |
|---|---|---|
| Muscle recovery and injury | Not graded | Peptides marketed for muscle recovery include BPC-157, TB-500, PEG-MGF, IGF-1 LR3, and growth hormone secretagogues. Human evidence for muscle healing is absent for all of them; the supporting data are rodent muscle transection models and mechanistic cell work. Several are WADA prohibited. |
| Muscle wasting and sarcopenia | Evidence: Animal-only evidence | Follistatin gene therapy (not the injectable peptide) improved walking in a handful of patients with muscle disease; those results do not raise the grade for injectable follistatin-344. |
Is Follistatin-344 legal in the United States?
FDA and compounding status
Follistatin-344 has never been submitted to or reviewed by FDA as a drug and does not appear on the 503A bulk drug substance Category 1, 2, or 3 lists or the 503B bulks list as of the last verification date. It is a biologic sized protein rather than a small peptide, so even a nomination would face the biologics compounding limits. There is no approved product and no lawful compounding pathway; products sold online are labeled for research use only.
WADA status
WADA prohibited. Athletes subject to anti-doping testing should treat this as prohibited at all times unless the current prohibited list says otherwise.
Regulatory timeline
No regulatory events recorded.
Full tracker for Follistatin-344 or the category-wide tracker.
What published studies of Follistatin-344 used
Ranges below are reported from published studies and labeling only. PeptideAgent does not recommend doses or protocols.
Not established in human literature for the injected peptide. The only human dosing data are for AAV1-FS344 gene therapy, given as a single intramuscular series of 6 x 10^11 to 1.2 x 10^12 vector genomes per kg into the quadriceps, which does not translate to any peptide dose. Products sold as follistatin-344 for injection have no dose finding data of any kind.
Routes reported
| # | Route |
|---|---|
| 1 | Subcutaneous or intramuscular injection (as sold, no human data) |
| 2 | Intramuscular AAV1 gene therapy (clinical trials only) |
| 3 | Transgenic overexpression and intramuscular viral vector (animal studies) |
What are the side effects and interactions of Follistatin-344?
Side effects
| # | Reported side effect |
|---|---|
| 1 | No human safety data for injected follistatin-344 |
| 2 | Follistatin binds activins that regulate FSH release, so suppression of fertility hormones is a theoretical concern (not seen in the 15 month macaque study) |
| 3 | Activin and follistatin regulate wound healing, inflammation, and liver regeneration, so off target effects are plausible and untested |
| 4 | Products sold as research chemicals are unverified for identity, purity, and endotoxin |
Interactions
| # | Interaction |
|---|---|
| 1 | No human interaction studies exist |
| 2 | Theoretical additive muscle growth and hormonal effects when combined with other myostatin pathway agents, growth hormone secretagogues, or IGF-1 analogs; none tested |
Contraindications
| # | Contraindication |
|---|---|
| 1 | Competitive athletes subject to WADA testing (prohibited at all times as a myostatin inhibitor) |
| 2 | Pregnancy, planned conception, and breastfeeding (activin signaling is essential for reproduction; no data) |
| 3 | Active cancer (activin and follistatin signaling affect tumor growth in both directions; no data) |
| 4 | Anyone: no lawful human product exists |
How do people access Follistatin-344 legally?
Typical cost: Not available through licensed channels. Research chemical listings for 1 mg vials are not lawful for human use and are not verified for identity or purity.
Verified access options
Step 1
Not legally available for human use in the United States.
Step 2
Gene therapy form (AAV1-FS344) was available only inside registered clinical trials.
Step 3
Products labeled research use only are not lawful for human use and are not verified.
Access paths are verified against public regulatory records and prescriber licensing. We never list unlicensed vendors.
Compare Follistatin-344
What's actually offered, and what that means for you
Licensed compounding pharmacies, clinics, and telehealth prescribers openly offer many unapproved peptides, and prescribers write prescriptions for them. That does not make Follistatin-344 lawful. Follistatin-344 is not FDA approved and not on the 503A bulks list, so a pharmacy has no lawful basis to compound it. [5] [7]
Enforcement is uneven. FDA mostly acts through warning letters to compounders and online sellers, Category 2 safety listings, and import alerts that let it detain shipments, rather than stopping every pharmacy. State pharmacy boards oversee pharmacies day to day, and their rules differ. [7] [8] [9] [10] [11]
What changes for you
- No FDA review of the product: FDA does not check a compounded drug's safety, effectiveness, or quality before it is sold. [11]
- Identity, purity, sterility, and dose accuracy can vary from batch to batch. [7]
- Insurance rarely covers it, so you usually pay cash.
- For tested athletes, Follistatin-344 is prohibited at all times on the WADA list, whatever the source. [6]
What to check
These checks lower some risks, but they do not make an unlawfully compounded product lawful or safe. Check for:
- A 503A pharmacy licensed in your state (your state board of pharmacy publishes license lookups). [11]
- A real evaluation by a licensed prescriber, not just an online form.
- A certificate of analysis for the specific batch.
Frequently asked questions
Is follistatin-344 legal in the United States?
It is not an FDA approved drug, it is not on any FDA compounding bulks list (the lists of raw ingredients pharmacies may use to custom-make drugs), and there is no lawful way to obtain it for human use. Possessing it is not itself a crime, but selling it for human use is unlawful, and products labeled research use only are not tested for identity or purity. The only human exposure to follistatin has been inside registered gene therapy trials, which deliver the follistatin gene rather than the protein. [3] [5]
Does follistatin-344 build muscle in humans?
Unknown. The dramatic muscle gains come from mice (194% to 327% larger muscles when follistatin was overexpressed) and macaques (larger, stronger quadriceps for 15 months after a gene therapy injection). In people, two open label gene therapy trials of 6 patients each reported better 6 minute walk distances in muscular dystrophy and inclusion body myositis, but there was no placebo group and no muscle mass endpoint that would settle the question. Injected follistatin-344 peptide has never been tested in a published human trial. [1] [2] [3] [4]
What are the side effects of follistatin-344?
There is no human safety data for the injected peptide. The concerns are mechanistic: follistatin also neutralizes activins, which control FSH release and fertility, wound healing, inflammation, and liver regeneration. The 15 month macaque gene therapy study found no change in reproductive hormones or organ histology, and the two small human gene therapy trials reported no serious adverse events, but those were local muscle injections of a vector, not systemic peptide. Unverified research chemical products add contamination and endotoxin risk. [2] [3] [4]
How is follistatin-344 taken?
In the only human studies it was not injected as a peptide at all: patients received a one time series of AAV1 vector injections into the quadriceps that made muscle cells produce follistatin. Products sold as follistatin-344 are lyophilized protein for subcutaneous or intramuscular injection, and no human dose finding, pharmacokinetic, or safety study exists for that route. A 344 amino acid glycoprotein is also large and fragile enough that purity and folding of unregulated products is a real question. [2] [3]
How much does follistatin-344 cost?
There is no licensed product and no compounding pathway, so there is no legitimate price. Research chemical sellers list 1 mg vials, but those products are not lawful for human use and are not verified for identity, purity, or biological activity, which for a folded 344 amino acid protein is not guaranteed. PeptideAgent does not track gray market pricing. [5]
Is follistatin-344 banned by WADA?
Yes. The WADA Prohibited List names follistatin explicitly under section S4 (hormone and metabolic modulators) as a myostatin binding protein among agents preventing activin receptor IIB activation. It is prohibited at all times, in and out of competition, for every athlete subject to the Code. [6]
Follistatin-344 vs ACE-031: what is the difference?
Both block the myostatin and activin pathway but from different sides. Follistatin is the natural binding protein that soaks up myostatin and activins; ACE-031 is a soluble copy of the receptor (ActRIIB) fused to an antibody fragment that does the same job. ACE-031 has published placebo controlled human trials and known bleeding and vascular side effects that halted its development; follistatin has only animal data and open label gene therapy pilots. Neither is approved or lawfully available, and both are WADA prohibited. [1] [4] [6]
Is follistatin gene therapy the same as injecting follistatin-344?
No. The gene therapy trials injected an AAV1 vector carrying the FS344 gene into thigh muscle so the muscle would produce the 315 isoform of follistatin locally for years. Injecting the protein itself gives a short lived systemic exposure with a different distribution, and there is no human evidence that it produces any of the effects seen with gene delivery. Marketing that cites the gene therapy trials to sell injectable peptide is comparing two different things. [2] [3]
Decisions about starting, stopping, or combining any treatment belong with a licensed clinician who knows your history.
From the blog
- Peptides for muscle growth, ranked by human evidence
MK-677, sermorelin, tesamorelin, CJC-1295, IGF-1 LR3, and more ranked by human evidence. None is approved for muscle growth, and all ten are banned in tested sport.
Sources
Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.
- [1]Lee SJ, McPherron AC. Regulation of myostatin activity and muscle growth. Proc Natl Acad Sci USA 2001PubMed 11459935, 2001
- [2]Kota J et al. Follistatin gene delivery enhances muscle growth and strength in nonhuman primates. Sci Transl Med 2009PubMed 20368179, 2009
- [3]Mendell JR et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy. Mol Ther 2015PubMed 25322757, 2015
- [4]Mendell JR et al. Follistatin gene therapy for sporadic inclusion body myositis improves functional outcomes. Mol Ther 2017PubMed 28279643, 2017
- [5]FDA: Bulk drug substances used in compounding under section 503A of the FD&C Act (links to the Category 1, 2, and 3 lists and the bulks list)FDA, 2026
- [6]WADA Prohibited List, section S4 hormone and metabolic modulators (names follistatin as a myostatin binding protein)WADA, 2026
- [7]FDA: Certain bulk drug substances for use in compounding may present significant safety risks (Category 2)FDA
- [8]FDA: Compounding inspections, recalls, and other actions (warning letters to compounders)FDA
- [9]FDA warning letters database: July 30, 2019 letter to a 503A pharmacy that compounded BPC-157 acetate outside section 503AFDA, 2019
- [10]FDA Import Alert 66-41: Detention without physical examination of unapproved new drugs promoted in the U.S. (includes peptide entries)FDA
- [11]FDA: Compounding and the FDA, questions and answersFDA
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PeptideAgent. (2026, September 22). Follistatin-344: evidence, legality, and access. https://peptideagent.ai/peptides/follistatin-344- HTML link
<a href="https://peptideagent.ai/peptides/follistatin-344">Follistatin-344: evidence, legality, and access</a>, PeptideAgent, updated September 22, 2026.