Peptide education
Follistatin-344
Follistatin-344 is the follistatin precursor used as the payload in gene-therapy experiments, not a peptide that meaningfully comes in a vial. Follistatin itself is a glycoprotein that traps myostatin and activin-family ligands, the signals that brake muscle growth, which is why the name pulls in muscle-disease researchers and performance marketers at once. The human evidence behind the name is two small open-label studies that injected the FS344 gene into diseased muscle, six patients each. The gray market sells lyophilized powder under the same name, and published testing found that much of it did not contain follistatin at all.
Serious follistatin-344 research delivers the gene into muscle, in six-patient, open-label disease studies with mixed results. The 1 mg vials sold under the same name failed identity testing often enough that the label is close to a coin flip.
Overview
Quick answer
The name "Follistatin-344" gets used for several distinct things: the FST344 precursor transcript, AAV1.huFS344 gene-transfer constructs, sponsor-linked plasmid programs, recombinant research proteins, and gray-market lyophilized vials. A local disease gene-transfer study does not show that a retail or gray-market vial contains the same material, reaches the same tissue, or has the same safety profile.
What is Follistatin-344?
The precursor form of follistatin used in gene-transfer research: constructs like AAV1.CMV.FS344 are injected into muscle so the tissue produces follistatin itself. It is a 344-amino-acid glycoprotein precursor with isoform, folding, and glycosylation complexity, not a simple peptide where a label and a purity number settle identity.
Why is it discussed?
Follistatin binds and neutralizes myostatin and activins, two brakes on muscle growth, and animals given follistatin gene delivery grew larger, stronger muscle. That makes it a legitimate muscle-disease research direction and an easy performance-marketing hook, two conversations with very different evidence behind them.
What do studies actually use?
Gene transfer, not peptide injections. The Becker muscular dystrophy study injected AAV1.CMV.FS344 into quadriceps at 3 x 10^11 or 6 x 10^11 vector genomes per kilogram per leg with a prednisone taper; the inclusion body myositis study used 6 x 10^11 vg/kg with prednisone and an exercise program. Vector-genome dosing does not convert into milligrams in a vial.
What shows up in gray-market use?
Research-use 1 mg vials marketed around muscle growth, recovery, and myostatin inhibition, with community schedules near 100 mcg a day for 10 to 20 day runs. The safety signal that should be attached to that pattern is a retinal case series: central serous chorioretinopathy in 11 male bodybuilders who reported injecting full 1 mg vials. Read it as a warning, not a protocol.
How strong are the performance claims?
Weak at every step of the chain. The disease studies are six-patient open-label gene-transfer experiments, and one of them drew published criticism for confounding; healthy-user claims trace to sponsor-linked plasmid material at preprint level; and the retail product may not be follistatin in the first place.
Reported practice
Commonly reported protocol
Community myostatin-inhibitor protocols. Community-reported patterns, not verified by controlled human trials and not a use recommendation. Full use-pattern detail
Evidence
Evidence snapshot
Small open-label Becker muscular dystrophy and sporadic inclusion body myositis studies reported functional findings after intramuscular AAV follistatin gene transfer. They are not randomized consumer-performance studies.
Public healthy-subject and body-composition claims come mainly from registered or sponsor-linked plasmid materials and preprint-level commercial discussion, not independent confirmatory human evidence.
A black-market analysis of 17 products sold as follistatin found that only 9 contained follistatin; positive samples were His-tagged and showed a high degree of oligomerization.
FDA orphan-drug materials list an adeno-associated virus transgene of follistatin as not approved for the orphan indication, and a warning letter stated that compounded follistatin products were not eligible for the cited section 503A exemptions.
A case series described 11 male bodybuilders with central serous chorioretinopathy after reported complete 1 mg vial injections of follistatin-344. The report leaves product identity and causality unresolved, but it is a serious warning for gray-market use.
Claims
Common claims vs evidence
| Claim | Human evidence | Mechanistic evidence | Anecdotal evidence | Verdict |
|---|---|---|---|---|
| Follistatin-344 is a clinically established muscle-building peptide. | The human disease evidence is small, open-label, and gene-transfer based. In Becker muscular dystrophy, six participants received bilateral intramuscular AAV1.CMV.FS344; four improved on the six-minute walk test and two did not. In sporadic inclusion body myositis, six ambulatory participants received bilateral quadriceps rAAV1.CMV.huFS344 with prednisone and exercise, and the paper reported improved walking performance versus matched untreated subjects. | The mechanism supports muscle interest because follistatin can bind myostatin and activins, reducing signals that normally restrain muscle growth. Animal work and nonhuman-primate work make the mechanism look biologically plausible. | Online stores, clinic-style marketing, and forum discussions often treat the name as a muscle-growth, physique, recovery, or anti-aging tool. Those discussions usually do not document product identity, sterile manufacturing, dosing accuracy, or clinical benefit. | The supported claim is narrower: small disease gene-transfer studies are worth discussing, but gray-market Follistatin-344 is not a clinically established muscle-building peptide. |
| It works by blocking myostatin. | Human trials were not designed to isolate myostatin blockade as the only driver of outcomes. They tested local follistatin gene transfer in disease populations. | The myostatin statement is partly right but incomplete. Follistatin can bind myostatin, activins, and some related ligands, so the biology is broader than a single-target myostatin blocker. | Vendor and forum copy often shortens the biology to "myostatin inhibitor" because that phrase is easy to market for muscle gain. | Directionally true as a mechanism headline, but too narrow if it implies a clean, myostatin-only effect. |
| A research vial is equivalent to the clinical-study material. | The core studies used intramuscular AAV gene-transfer constructs with defined protocols, monitoring, prednisone handling, and disease-specific populations. That is not the same context as a lyophilized retail vial. | Follistatin is a folded, disulfide-rich glycoprotein with isoform, processing, tag, oligomer, potency, and glycosylation questions. A mass peak or HPLC purity line does not settle those questions. | Black-market products have been sold as FS344 and FS315, but a peer-reviewed analysis found frequent non-identity, substitution with other growth-promoting peptides, His-tagged material, and oligomerization. | Retail FS344 claims require evidence that the material is the intended biologic and has been characterized well enough to compare with the gene-transfer literature; a matching name is insufficient. |
| It is safe because the small trials reported few problems. | The Becker muscular dystrophy and inclusion body myositis papers reported limited short-term safety issues in tiny treated cohorts. That leaves long-term safety, systemic safety, reproductive safety, and gray-market product safety unresolved. | Follistatin biology reaches beyond muscle into activin signaling, fertility biology, inflammation, fibrosis, and tumor-related pathways. That broad footprint makes repeated systemic exposure hard to judge from small local gene-transfer studies. | The gray-market safety report is not reassuring. A retinal case series reported central serous chorioretinopathy in 11 bodybuilders after complete 1 mg vial injections of Follistatin-344. | Small disease studies did not reveal major short-term problems, while broader gray-market use remains poorly characterized and has a serious ocular warning. |
| Follistatin gene therapy improves body composition or aging markers. | Public materials include a healthy-subject FST344 plasmid study and sponsor-linked claims about lean mass, fat percentage, and epigenetic measures. The materials are not independent confirmatory clinical evidence, and the associated writeup is preprint-level. | Muscle and metabolic interest is biologically plausible because follistatin affects myostatin and activin-family signaling. Plausibility is not the same as an established anti-aging or body-composition therapy. | Commercial gene-therapy and wellness marketing uses these claims to make FST344 sound like a performance or longevity intervention. | Mentionable as sponsor-linked market activity, not as an established benefit. |
Bottom line
Main takeaway
Follistatin-344 is a gene-therapy research payload with tiny disease studies behind it, attached to a retail market that has repeatedly failed to contain what the label says.
Route decides everything: intramuscular AAV gene transfer, sponsor plasmid programs, recombinant protein, and subcutaneous gray-market vials are four different products with different risks. Only the first has human outcome data, and it is six patients.
Anchor on the Mendell Becker and sIBM studies with the Greenberg critique, then the Reichel black-market analysis and the retinal case series. Together they show why both the efficacy story and the product story are unstable.
Identity
What it is
The FST gene makes follistatin in several forms. FS344 is the precursor used as cargo in gene-transfer work; FS315 is the mature circulating form; FS288 stays tissue-bound. When a study says FS344, it almost always means a gene delivered into muscle, not a protein injected from a vial.
Follistatin works as an extracellular trap. It wraps around myostatin and activin dimers and covers the surfaces those ligands use to reach their receptors, and since myostatin normally restrains muscle growth, removing that signal in animals produces visibly larger muscle. That is the whole rationale, and it is real.
What the shorthand misses is scope. Activin blockade may carry part of the anabolic effect, and the same activin family touches reproductive biology, inflammation, fibrosis, and tumor pathways, so a systemic follistatin product is never a muscle-only intervention.
Identity is the practical wall. Follistatin is a disulfide-rich glycoprotein, and whether a product folds correctly, carries the right glycosylation, sits as a monomer or oligomer, and actually neutralizes ligand are all open questions for a retail vial. Papers, registries, vendors, and offshore clinics reuse the same few names for very different materials, which is how a gene-therapy literature ended up selling powder.
How people talk about it online
The online conversation is muscle first: myostatin inhibition, growth, recovery, fat loss, anti-aging. The clearest market pattern is the research-use 1 mg lyophilized vial, with community runs around 100 mcg a day for 10 to 20 days, a schedule extrapolated from animal pathway work rather than any human study.
Bodybuilding discussion matters to the safety record here, not just the demand side. The retinal case series involved male bodybuilders who reported subcutaneous full-vial 1 mg injections before central serous chorioretinopathy, with product identity unresolved.
A second thread is gray-zone gene-therapy marketing: registered and sponsor-linked FST344 plasmid programs talking about lean mass, body fat, and epigenetic measures. The support so far is commercial and preprint-level, with no independent confirmation.
Use context
Routes, doses, and cycle patterns
Documented study exposures come from intramuscular AAV disease studies, sponsor-linked plasmid programs, and safety reports. Retail-vial discussion often describes subcutaneous use, but the cited sources do not give a standard frequency or cycle.
Human studies and product labels
Becker muscular dystrophy AAV1.CMV.FS344 study
- Purpose
- Investigational muscle-disease gene transfer
- Context
- Open-label human disease study
- Route
- Bilateral intramuscular injection into quadriceps
- Amount
- 3 x 10^11 or 6 x 10^11 vector genomes per kilogram per leg
- Frequency
- Single gene-transfer administration as reported in the study
- Duration
- About 180 days of primary follow-up
Six participants were treated. Four improved on the six-minute walk test by 29 m to 125 m, while two did not improve. The study was small, open-label, and disease-specific.
Sporadic inclusion body myositis AAV1.huFS344 study
- Purpose
- Investigational functional improvement in sIBM
- Context
- Open-label human disease study with matched untreated comparison
- Route
- Bilateral intramuscular quadriceps injection
- Amount
- 6 x 10^11 vector genomes per kilogram
- Frequency
- Single gene-transfer administration as reported in the study
- Duration
- Day 180 biopsy and annualized walking-performance comparisons
The paper reported walking-performance improvement versus matched untreated subjects, but the design included prednisone and an exercise regimen and later drew published criticism about confounding and interpretation.
Duchenne muscular dystrophy study history
- Purpose
- Investigational protocol listing
- Context
- Trial protocol and registry materials
- Route
- Intramuscular injections into gluteal muscles, quadriceps, and tibialis anterior
- Amount
- Total dose 2.4 x 10^12 vector genomes per kilogram
- Frequency
- Study-plan administration
- Duration
- Study-plan follow-up
The protocol is included for development history. Public sources were not consistent enough to constitute efficacy evidence.
Healthy-subject FST344 plasmid program
- Purpose
- Body-composition and biomarker claims in a commercial development context
- Context
- Registered or sponsor-linked plasmid gene-therapy materials
- Route
- Injectable plasmid gene therapy
- Amount
- Single-dose approach; exact dose not consistently available
- Frequency
- Single-dose approach in the described materials
- Duration
- 3-month body-composition and biomarker endpoints
Sponsor-linked materials discuss lean mass, body fat, and epigenetic measures. They are market and development activity until independent peer-reviewed confirmation exists.
Real-world discussion
Community myostatin-inhibitor protocols
- Purpose
- Muscle growth discussion
- Context
- Forums, vendors, and protocol blogs
- Route
- Subcutaneous injection
- Amount
- Generally around 100 mcg per day for runs of 10 to 20 days
- Frequency
- Once daily during a run
- Duration
- Commonly described as 10 to 20 day cycles, repeated infrequently
Community schedules are extrapolated from animal myostatin-pathway work; the serious human research in this space is gene-therapy delivery, not peptide injection. Context, not a recommendation.
What varies
- Product type: AAV gene transfer tells you about local vector delivery, plasmid marketing tells you about a commercial program, recombinant protein raises biologic comparability questions, and retail vial claims mostly raise identity and sterility questions.
- Route: intramuscular local gene transfer and subcutaneous gray-market injection put very different material into very different exposure settings.
- Amount: Vector-genome dosing in trials cannot be translated into milligram vial use.
- Quality: Follistatin products require identity, potency, tag, oligomer, sterility, endotoxin, and biologic-characterization evidence.
- Source type: disease trials carry more evidentiary weight than registry listings, sponsor marketing, vendor pages, and safety case reports.
Human data
Human evidence
The peer-reviewed human record is two open-label gene-transfer studies of six patients each. In Becker muscular dystrophy, four of six improved on the six-minute walk by 29 to 125 meters and two did not; in sporadic inclusion body myositis, treated patients walked better than matched untreated patients, and that interpretation was then publicly criticized because prednisone and exercise were part of the design. A Duchenne protocol exists at registry level, and healthy-subject claims come from sponsor-linked plasmid material without independent peer review. Nothing in the record tests a retail FS344 vial, and nothing measures healthy-user performance.
Evidence maturity
Follistatin-344's human evidence stops at tiny open-label disease gene-transfer studies, while the retail market has documented product-identity failures.
Follistatin binds myostatin and activin-family ligands, and animal plus nonhuman-primate AAV work showed muscle effects.
Open-label AAV1-FS344 studies in Becker muscular dystrophy and sporadic inclusion body myositis treated six patients each, and the sIBM interpretation was later contested.
None found; healthy performance and body-composition claims rest on registry, sponsor-linked, or preprint-level materials.
No approved follistatin product exists, and black-market testing found many products sold as follistatin did not contain it.
| Study / evidence area | Population | Design | Product context | Main outcome | Limitations | Weight |
|---|---|---|---|---|---|---|
| Becker muscular dystrophy AAV1.CMV.FS344 study | Six participants with Becker muscular dystrophy | Open-label human disease gene-transfer study | Investigational intramuscular AAV gene-transfer construct | Four participants improved on the six-minute walk test by 29 m to 125 m over roughly 180 days, while two did not improve; the paper reported no adverse effects in this tiny cohort. | No placebo group, very small sample, disease-specific population, and no basis for translating the regimen to ordinary retail-vial use. | weak |
| Sporadic inclusion body myositis AAV1.CMV.huFS344 study | Six ambulatory participants with sporadic inclusion body myositis | Open-label human disease study with matched untreated comparison | Investigational intramuscular AAV gene-transfer construct | The paper reported improved annualized six-minute-walk performance versus matched untreated subjects after bilateral quadriceps gene transfer. | Nonrandomized, tiny, open-label, confounded by prednisone and exercise, and later criticized for interpretation and reporting issues. | weak |
| Duchenne muscular dystrophy study record | Duchenne muscular dystrophy study context | Protocol and registry materials | Investigational intramuscular AAV1.CMV.huFollistatin344 | Public materials describe a total 2.4 x 10^12 vector genomes per kilogram dose divided among gluteal, quadriceps, and tibialis anterior muscles. | Public sources are protocol-focused and inconsistent for outcome reporting, so this is not an efficacy claim. | weak |
| Healthy-subject FST344 plasmid materials | Healthy-subject trial and sponsor-linked commercial context | Registry, sponsor-linked materials, and preprint-level report | Injectable plasmid gene-therapy program | Public materials discuss 3-month body-composition, serum-follistatin, and epigenetic endpoints with commercial claims around lean mass and fat percentage. | Not independent confirmatory evidence and not a peer-reviewed foundation for performance, body-composition, or anti-aging claims. | anecdotal |
| Central serous chorioretinopathy case series | Eleven male bodybuilders who reported complete 1 mg vial injections of Follistatin-344 | Retrospective case series | Gray-market or non-study subcutaneous use reports | The series reported central serous chorioretinopathy after complete 1 mg vial injections of Follistatin-344. | Product identity, causality, co-exposures, and dose verification cannot be fully resolved, but the report is clinically important. | anecdotal |
Cautions
Safety and unknowns
- Small disease gene-transfer studies reported limited short-term safety issues, but those cohorts are too small to define broader safety.
- The retinal case series in bodybuilders raises concern about ocular effects after reported complete 1 mg vial injections, even though product identity and causality remain uncertain.
- Follistatin affects activin-family biology as well as myostatin, so fertility, endocrine, inflammatory, fibrotic, and tumor-biology questions remain important.
- Repeated systemic exposure from gray-market products has not been studied like a regulated biologic or approved drug product.
- Product contaminants, endotoxin, sterility failures, wrong active ingredient, His-tagged constructs, oligomers, and potency failures may change the safety profile completely.
Product quality
A vial label is only a starting point
Follistatin-344 is unusually vulnerable to product-identity confusion because it is a complex protein/glycoprotein context rather than a simple short peptide.
In one black-market analysis, only 9 of 17 products sold as follistatin actually contained follistatin, and positive samples were His-tagged and highly oligomerized.
A basic retail COA that lists HPLC purity or mass still leaves native structure, tag status, monomeric state, potency, glycosylation, sterility, endotoxin control, and comparability to trial constructs to be documented.
Identity
Published black-market testing found products that did not contain follistatin and some that contained other growth-promoting peptides.
Tag status
His-tagged recombinant material can behave differently from native endogenous follistatin biology.
Oligomer state
High oligomerization can change potency, exposure, immune risk, and comparability to studied material.
Potency
Purity alone cannot show functional neutralization of activin or myostatin.
Sterility and endotoxin
Injectable biologic-style material requires contamination controls that ordinary vendor pages often do not document.
Mechanism
How it is proposed to work
Follistatin acts like an extracellular trap for certain growth-factor signals. By binding ligands such as myostatin and activins, it can block those signals from reaching their receptors. Myostatin normally restrains muscle growth, so reducing that signal is the main reason people associate follistatin with muscle gain.
Structural studies show follistatin wrapping around activin or myostatin dimers and covering receptor-binding surfaces. That supports the ligand-trap explanation.
The "myostatin blocker" shorthand misses important biology. Activin blockade may contribute to anabolic effects, and broader activin/TGF-beta signaling also touches reproductive, inflammatory, fibrotic, and tumor contexts.
Isoform handling matters. FS344 is a precursor construct used in gene-transfer work, while mature circulating follistatin biology is often tied to FS315. FS288 is more tissue-bound because of stronger heparan-sulfate interaction.
Follistatin binds and neutralizes myostatin and related TGF-beta family ligands, so blocking those ligands removes a brake on muscle growth: real biology in animals, but injected peptide delivery is not how the serious human programs (AAV gene therapy) approach it.
FAQ
Common questions
Does follistatin-344 build muscle?
The myostatin-inhibition mechanism is real in animals — blocking myostatin does increase muscle mass in animal models. There are no human trials of injected follistatin-344 for physique purposes, so the human claim is extrapolation.
What amounts get discussed online?
Community protocols commonly describe around 100 mcg per day for 10 to 20 day cycles, repeated infrequently.
Is this the same as follistatin gene therapy?
No. The serious human research delivers follistatin via AAV gene therapy in muscular-dystrophy programs. That is a different modality, population, and evidence base from injected peptide products.
Details
Technical details
Sources
References
- 1.
NCBI FST gene. NCBI Gene 10468, FST follistatin.
Primary database
- 2.
Follistatin isoform activity. Sidis Y et al. Biological activity of follistatin isoforms and follistatin-like-3.
Primary paper
- 3.
Activin-follistatin structure. Harrington AE et al. Structural basis for the inhibition of activin signalling by follistatin.
Primary paper
- 4.
Follistatin therapy review. Rodino-Klapac LR et al. Inhibition of myostatin with emphasis on follistatin as a therapy.
Review with translational synthesis
- 5.
Primate FS344 gene delivery. Kota J et al. Follistatin gene delivery enhances muscle growth and strength in nonhuman primates.
Primary paper
- 6.
Becker FS344 trial. Mendell JR et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy.
Primary paper
- 7.
sIBM FS344 trial. Mendell JR et al. Follistatin Gene Therapy for Sporadic Inclusion Body Myositis Improves Functional Outcomes.
Primary paper
- 8.
Greenberg sIBM critique. Greenberg SA. Unfounded Claims of Improved Functional Outcomes Attributed to Follistatin Gene Therapy in Inclusion Body Myositis.
Critique letter
- 9.
sIBM author reply. Reply to Letter to the Editor on follistatin IBM study.
Reply letter
- 10.
SCGE trial summary. NCT01519349 and SCGE trial report.
Registry / official trial summary
- 11.
DMD FS344 registry. NCT02354781 protocol and public trial materials.
Protocol / registry source
- 12.
FDA orphan designation. FDA Orphan Drug Designations and Approvals, adeno-associated virus transgene of follistatin.
FDA official
- 13.
FDA Tailor Made letter. FDA warning letter to Tailor Made Compounding LLC.
FDA official
- 14.
Black-market FS344 analysis. Reichel C et al. Detection of black market follistatin 344.
Primary paper
- 15.
Ocular case series. Dağ U et al. Central serous chorioretinopathy associated with high-dose follistatin-344.
Primary case series
- 16.
R&D Systems FS315 datasheet. R&D Systems recombinant human follistatin 315 datasheet.
Supplier technical datasheet
- 17.
FDA and ICH biologics quality. FDA and ICH Q6B biologics-quality guidance.
Official guidance
- 18.
FTC claims guidance. FTC Health Products Compliance Guidance.
FTC official
- 19.
NCT06411366 listing. Public trial listing for NCT06411366.
Registry mirror / public listing
- 20.
FST plasmid preprint. Sponsor-linked FST plasmid preprint and website materials.
Sponsor-linked preprint / marketing
- 21.
medRxiv disclaimer. medRxiv preprint disclaimer.
Preprint platform
- 22.
CALM-AF-AI listing. CALM-AF-AI public trial listing.
Public trial listing
- 23.
FS344 vendor listings. Vendor listings for “research-use-only” follistatin-344.
Vendor / gray-market
- 24.
Activin and inflammation review. Hedger MP et al. Regulation and functions of activin and follistatin in inflammation and fibrosis.
Review
- 25.
Fst isoform fertility note. Mouse Fst gene note, fertility defects when only certain isoforms remain.
Primary gene summary
- 26.
Follistatin tumor review. Shi L et al. Clinical and Therapeutic Implications of Follistatin in Solid Tumours.
Review