What Is Follistatin-344? Uses, Benefits, Safety, FDA Status, and Evidence
Medical review note: This article is for educational purposes only and does not provide medical advice. Follistatin-344 is not FDA-approved for human therapeutic use. Products sold online as Follistatin-344, FST-344, FS344, follistatin peptide, myostatin inhibitor, muscle-growth peptide, gene-therapy follistatin, or “research use only” Follistatin-344 may carry serious safety, quality, legal, and anti-doping risks.
Quick answer
Follistatin-344, often written FST-344 or FS344, is a follistatin gene/transcript form used in research and gene-transfer studies. Follistatin is a naturally occurring glycoprotein that binds and inhibits members of the TGF-beta superfamily, especially activin and myostatin. Because myostatin limits muscle growth, follistatin has been studied as a way to increase muscle mass and improve muscle function in animal models and rare muscle-disease gene-therapy trials. However, Follistatin-344 is not FDA-approved, online injectable FST-344 products are not equivalent to controlled gene-therapy research, and black-market product testing has found major identity and content problems. WADA prohibits follistatin and other myostatin inhibitors in sport.
Key facts about Follistatin-344
| Question | Answer |
|---|---|
| What is Follistatin-344? | A follistatin gene/transcript form, often used in gene-transfer research to produce follistatin protein, especially the circulating FST315 isoform. |
| Other names | FST-344, FS344, Follistatin 344, huFS344, AAV1-FS344, AAV1.CMV.huFS344, follistatin gene therapy. |
| Peptide/protein class | Follistatin glycoprotein / activin-binding protein / myostatin inhibitor / TGF-beta superfamily modulator. |
| Main mechanism | Binds and inhibits myostatin and activin, reducing signaling that normally restrains skeletal muscle growth and influences inflammation, reproduction, metabolism, and tissue remodeling. |
| FDA-approved? | No. Follistatin-344 is not an FDA-approved drug. |
| Main studied uses | Becker muscular dystrophy, sporadic inclusion body myositis, Duchenne muscular dystrophy gene-transfer research, muscle growth, muscle repair, myostatin inhibition, aging/body-composition research, and tissue-regeneration biology. |
| Human evidence level | Limited and investigational. Small gene-therapy studies exist in rare muscle disorders, but strong consumer-use evidence is lacking. |
| Animal/lab evidence level | Moderate to strong preclinical evidence for muscle-mass, muscle-strength, repair, and myostatin/activin-inhibition mechanisms. |
| Common online claims | “Muscle-growth peptide,” “myostatin blocker,” “bodybuilding peptide,” “longevity gene therapy,” “lean-mass peptide,” “recovery peptide,” “anti-aging peptide.” |
| Sports status | Prohibited by WADA. WADA lists myostatin-binding proteins such as follistatin as prohibited myostatin inhibitors. |
| Main safety concern | Lack of FDA approval, gene-transfer uncertainty, myostatin/activin pathway disruption, reproductive/endocrine concerns, tumor-biology concerns, immune responses, black-market product mislabeling, and anti-doping prohibition. |
What is Follistatin-344?
Follistatin-344 is a follistatin gene/transcript form associated with research into follistatin expression and myostatin inhibition. In many scientific contexts, FS344 refers to the follistatin transgene used in gene-transfer studies. That transgene encodes a follistatin protein isoform commonly discussed as FST315.
Follistatin itself is a naturally occurring glycoprotein encoded by the FST gene. It was originally known as an activin-binding protein because it binds activin and blocks activin signaling. It also inhibits myostatin, a TGF-beta family protein that limits skeletal muscle growth.
A PMC preclinical gene-delivery paper describes use of the human FS344 transgene in nonhuman primates and notes that previous studies used AAV1 expressing human FS344 to increase muscle mass and strength in animal models.
A PMC phase 1/2a Becker muscular dystrophy trial studied intramuscular gene transfer of rAAV1.CMV.huFollistatin344.
The key distinction:
Follistatin-344 is not a simple injectable “muscle peptide.” In the stronger clinical literature, it is usually part of gene-transfer research, not a routine peptide medication.
How does Follistatin-344 work?
Follistatin-344 works through follistatin biology.
Follistatin binds proteins in the TGF-beta superfamily, especially:
- Myostatin
- Activin A
- Other activin-related ligands
- Some growth differentiation factors depending on context
Myostatin normally limits skeletal muscle growth. When follistatin inhibits myostatin, the biological brake on muscle growth can be reduced. That is why follistatin has been studied for muscle-wasting disorders and why it attracts bodybuilding and biohacking attention.
In plain English:
Follistatin-344 is studied because increasing follistatin activity can block signals that normally restrict muscle growth.
But this pathway is not narrow.
Activin and myostatin signaling are involved in more than muscle size. They also intersect with:
- Reproductive hormone biology
- Follicle-stimulating hormone regulation
- Inflammation
- Fibrosis
- Metabolism
- Tissue repair
- Tumor biology
- Organ development and remodeling
That means the online framing of FST-344 as “just a myostatin blocker” is too simplistic.
What is Follistatin-344 used for?
Follistatin-344 is investigational. It is not FDA-approved for any use.
| Use | Evidence level | What is known | What is not known | |---|---|---| | Becker muscular dystrophy gene therapy | Small phase 1/2a human evidence | AAV1-FS344 gene-transfer studies reported encouraging findings in small BMD cohorts. | Not FDA-approved; larger controlled trials and long-term safety data are needed. | | Sporadic inclusion body myositis | Small investigational human evidence with dispute | A small trial reported functional improvements, but published criticism challenged the strength of the claims. | Not an approved IBM therapy and efficacy remains uncertain. | | Duchenne muscular dystrophy | Early clinical/research context | ClinicalTrials.gov lists AAV1.CMV.huFollistatin344 work in DMD. | No FDA-approved FST-344 DMD therapy. | | Muscle growth | Strong preclinical rationale | Follistatin overexpression can increase muscle mass in animal models. | Human bodybuilding or enhancement benefit is not established or approved. | | Muscle injury repair | Preclinical | Animal studies suggest improved skeletal muscle healing after injury. | Human injury-recovery benefit is not established. | | Sarcopenia / aging | Speculative / preclinical | Myostatin inhibition is relevant to age-related muscle loss research. | Consumer longevity or anti-aging claims are not proven. | | Fat loss / body composition | Weak to early | Some commercial gene-therapy claims exist. | Independent, peer-reviewed, approval-level evidence is lacking. | | Fertility or reproductive biology | Mechanistic | Follistatin affects activin/FSH-related biology. | It is not an approved fertility therapy and pathway disruption could be risky. | | Online research-use FST-344 | High risk | Sold as powders, injections, or “gene therapy” services. | Identity, purity, sterility, concentration, delivery system, and legality may be unknown. |
What does the research show?
Preclinical muscle-growth evidence
Follistatin has strong preclinical evidence as a myostatin-pathway antagonist.
A PMC review on myostatin inhibition and follistatin describes follistatin as a powerful antagonist of myostatin that can increase muscle mass and strength.
A PMC animal study reported long-term enhancement of skeletal muscle mass and strength by single gene administration of myostatin inhibitors, including follistatin-related approaches.
The practical interpretation:
Follistatin biology can increase muscle mass in animal models, but animal muscle growth does not prove safe human enhancement.
Follistatin gene therapy in Becker muscular dystrophy
A phase 1/2a follistatin gene-therapy trial in Becker muscular dystrophy used rAAV1.CMV.huFollistatin344 and reported encouraging proof-of-principle findings.
A PubMed record of the same trial describes use of follistatin to inhibit the myostatin pathway in Becker muscular dystrophy.
The practical interpretation:
FST-344 has legitimate rare-disease gene-therapy research, but a small disease trial is not proof that FST-344 is safe or effective for consumer muscle-building.
Follistatin gene therapy in inclusion body myositis
A PubMed study in sporadic inclusion body myositis reported promise for follistatin gene therapy in mild to moderately affected ambulatory patients.
However, this evidence has been challenged. A PubMed commentary titled “Unfounded Claims of Improved Functional Outcomes Attributed to Follistatin Gene Therapy in Inclusion Body Myositis” argued that claims of improved functional outcomes were not adequately supported.
The practical interpretation:
The inclusion body myositis evidence is not settled. It should not be cited as clean proof that FST-344 works in humans.
Muscle injury and repair evidence
A PMC study on skeletal muscle healing after injury reported that follistatin improved skeletal muscle healing after injury in experimental models.
The practical interpretation:
Follistatin has repair-related biology, but injury-healing claims for consumer FST-344 remain unproven.
Black-market Follistatin-344 product evidence
Black-market FST-344 products are a major problem.
A PubMed study on black-market Follistatin-344 products investigated FS344 black-market products and developed detection methods. A related WADA research page states that only 9 of 17 tested black-market products actually contained the protein.
The practical interpretation:
Online Follistatin-344 products are not reliable. Many may not contain what they claim, and those that do may still have purity, sterility, dose, and safety problems.
FDA status
Follistatin-344 is not FDA-approved.
There is no FDA-approved Follistatin-344 product for muscle growth, bodybuilding, sarcopenia, aging, fat loss, recovery, Duchenne muscular dystrophy, Becker muscular dystrophy, inclusion body myositis, or any other use.
The practical interpretation:
Follistatin-344 remains investigational and should not be marketed as an approved therapeutic peptide.
Sports and anti-doping evidence
Follistatin is clearly relevant to anti-doping.
The WADA Prohibited List lists myostatin inhibitors as prohibited, including myostatin-binding proteins such as follistatin. The 2026 WADA Prohibited List PDF also includes myostatin-binding proteins such as follistatin under prohibited agents.
WADA also has a specific research page on detection of follistatin doping, describing follistatin as a myostatin-inhibiting protein prohibited under the WADA Prohibited List.
The practical interpretation:
For athletes, Follistatin-344 is not a gray area. Follistatin and related myostatin-inhibiting strategies are prohibited.
Evidence summary
| Claim | Evidence verdict | Explanation |
|---|---|---|
| “Follistatin-344 inhibits myostatin.” | Supported mechanistically | Follistatin inhibits myostatin and other TGF-beta family ligands. |
| “Follistatin-344 increases muscle mass.” | Supported preclinically | Animal and gene-transfer studies support muscle-mass effects. |
| “FST-344 is FDA-approved.” | False | No FDA-approved Follistatin-344 drug exists. |
| “FST-344 is proven for bodybuilding.” | False | Human enhancement evidence is lacking and sports use is prohibited. |
| “FST-344 treats Becker muscular dystrophy.” | Investigational | Small gene-therapy studies exist, but it is not approved. |
| “FST-344 treats inclusion body myositis.” | Not established | A small study reported promise, but claims were challenged in published commentary. |
| “FST-344 heals muscle injuries.” | Preclinical only | Animal injury models exist, but human injury-treatment evidence is lacking. |
| “FST-344 is safe because follistatin is natural.” | False | Natural protein biology does not prove safety when artificially increased or delivered. |
| “Online FST-344 products are reliable.” | False | Black-market testing found many products did not contain the claimed protein. |
| “FST-344 is allowed in sport.” | False | WADA prohibits myostatin-binding proteins such as follistatin. |
Is Follistatin-344 FDA-approved?
No. Follistatin-344 is not FDA-approved.
There is no FDA-approved Follistatin-344 product for:
- Muscle growth
- Bodybuilding
- Fat loss
- Body recomposition
- Sarcopenia
- Anti-aging
- Longevity
- Athletic recovery
- Tendon or ligament repair
- Becker muscular dystrophy
- Duchenne muscular dystrophy
- Inclusion body myositis
- Any human therapeutic use
The key distinction:
FST-344 has legitimate experimental gene-therapy research, but it is not an approved medication or consumer peptide.
Is Follistatin-344 legal?
Follistatin-344’s legal status depends on product type, jurisdiction, intended use, delivery system, and whether it is part of an authorized clinical trial.
For U.S. readers:
Follistatin-344 is not an FDA-approved drug, and online availability does not mean it is legally marketed for human therapeutic or enhancement use.
Gene therapy adds another layer. A controlled AAV or plasmid gene-transfer study is not the same as buying a vial of FST-344 powder or receiving an unapproved commercial gene-therapy procedure.
The practical distinction:
| Product type | What it means |
|---|---|
| Endogenous follistatin | Naturally occurring human protein. |
| FST-344 transgene research | Experimental gene-transfer strategy used in controlled research. |
| FDA-approved Follistatin-344 | Does not currently exist. |
| Research-use FST-344 | Not an FDA-approved consumer therapeutic product. |
| Online injectable FST-344 | High risk for identity, purity, sterility, concentration, and safety problems. |
| Commercial “longevity gene therapy” | Not equivalent to FDA-approved gene therapy. |
The blunt version:
Buying “research use only” Follistatin-344 online is not the same as receiving an FDA-approved prescription medication or regulated gene therapy.
Is Follistatin-344 banned in sports?
Yes. Follistatin-344 is prohibited in sport.
WADA prohibits myostatin inhibitors, including myostatin-binding proteins such as follistatin. Because Follistatin-344 is used to increase follistatin activity and inhibit myostatin/activin signaling, it falls directly into the anti-doping concern area.
The practical advice:
Athletes subject to anti-doping rules should not use Follistatin-344, follistatin gene therapy, FST-344, or related myostatin-inhibition products.
Safety and side effects
Follistatin-344 should be treated as high risk.
Possible or theoretical risks include:
- Injection-site reactions
- Immune or allergic reactions
- Gene-transfer immune responses
- Vector-related risks for AAV or plasmid-based products
- Uncontrolled or uneven tissue expression
- Unknown long-term effects
- Myostatin/activin pathway disruption
- Reproductive hormone effects
- FSH/activin-related endocrine effects
- Fertility-related uncertainty
- Tendon, ligament, or connective-tissue imbalance if muscle increases faster than support tissue
- Organ-specific effects from broad TGF-beta pathway modulation
- Tumor-biology concerns because follistatin and activin pathways interact with cancer biology
- Product mislabeling
- Product contamination
- Incorrect protein identity or concentration
- Sterility and endotoxin risks
- Anti-doping violations
The biggest safety issue is not just side effects. It is biological scope.
Follistatin does not only affect muscle. It affects broad signaling pathways that matter in reproduction, development, inflammation, tissue remodeling, and disease biology.
Follistatin-344 vs similar peptides, proteins, and drugs
| Compound | Category | Main difference |
|---|---|---|
| Follistatin-344 / FST-344 | Follistatin gene/transcript form / myostatin inhibitor | Used in gene-transfer research; inhibits myostatin and activin pathways; not FDA-approved. |
| FST315 | Follistatin protein isoform | Circulating follistatin isoform commonly associated with FS344 transgene expression. |
| FST288 | Follistatin protein isoform | More tissue-bound due to stronger heparin-binding properties; different distribution. |
| Follistatin-like 3 / FSTL3 | Activin-binding protein | Related but distinct protein with different structure and biology. |
| Myostatin / GDF-8 | Muscle-growth inhibitor | Target inhibited by follistatin; naturally limits muscle growth. |
| ACE-031 | Soluble activin receptor fusion protein | Experimental myostatin/activin-pathway inhibitor, not the same as follistatin. |
| Bimagrumab | Activin receptor antibody | Investigational/clinical myostatin-pathway-related drug; different mechanism. |
| Thymosin Beta-4 / TB-500 | Tissue-repair peptide | Repair/actin-related peptide, not a myostatin-binding protein. |
| IGF-1 LR3 | Growth-factor analog | Growth-factor pathway, not follistatin/myostatin inhibition. |
| Growth hormone secretagogues | GH-axis peptides | Increase GH signaling indirectly; different pathway and risk profile. |
The key distinction:
Follistatin-344 belongs in the myostatin/activin inhibition category, not the ordinary peptide-recovery category.
Why is Follistatin-344 sold as “research use only”?
Some online sellers use “research use only” language to sell FST-344 outside normal drug channels.
That label is not a trust signal.
A serious reader should understand this distinction:
| Product type | What it means |
|---|---|
| Laboratory FST-344 | Research material used in controlled experimental settings. |
| AAV1.CMV.huFollistatin344 | Experimental gene-transfer construct used in clinical research. |
| FDA-approved FST-344 | Does not currently exist. |
| Research-use FST-344 | Not an FDA-approved consumer therapeutic product. |
| Black-market FST-344 | High risk. Product testing found many samples did not contain the claimed protein. |
| FST-344 gene therapy abroad | Not equivalent to FDA-approved gene therapy. |
How to evaluate Follistatin-344 claims online
| Claim | What to verify |
|---|---|
| “FDA-approved FST-344” | False. Follistatin-344 is not FDA-approved. |
| “Clinically proven muscle-growth peptide” | Look for controlled human trials, not animal studies or marketing claims. |
| “Safe myostatin blocker” | False as a blanket claim. Myostatin/activin biology is broad and safety is not established. |
| “Same as natural follistatin” | Misleading. Artificial delivery or overexpression is not the same as normal physiology. |
| “Legal for athletes” | False. WADA prohibits myostatin-binding proteins such as follistatin. |
| “Treats muscular dystrophy” | Investigational. Small gene-therapy studies exist, but no FDA approval exists. |
| “Reverses aging” | Unsupported. Longevity claims are not proven by approval-level evidence. |
| “Builds muscle without training” | Unsupported and overhyped. |
| “Research use only” | This does not mean safe, legal, approved, or appropriate for human use. |
| “Third-party tested” | Ask for batch-specific identity, purity, LC-MS, HPLC, sterility, endotoxin, microbial, and stability data. |
| “Gene therapy is temporary, so it is safe” | False. Temporary expression does not eliminate immune, pathway, or long-term uncertainty. |
Bottom line
Follistatin-344 is a follistatin gene/transcript form used in myostatin-inhibition and gene-transfer research. The biology is real: follistatin can inhibit myostatin and activin signaling, and preclinical studies show effects on muscle mass, muscle strength, and repair. Small human gene-therapy studies exist in rare muscle disorders.
The most defensible conclusion is:
Follistatin-344 is a serious experimental myostatin-inhibition technology, not a proven consumer muscle-building peptide. It is not FDA-approved, online products are unreliable and risky, and WADA prohibits follistatin and other myostatin inhibitors in sport.
FAQ
What is Follistatin-344?
Follistatin-344, also called FST-344 or FS344, is a follistatin gene/transcript form used in research and gene-transfer studies to increase follistatin activity.
What does Follistatin-344 do?
Follistatin-344 is used to increase follistatin activity. Follistatin binds and inhibits myostatin and activin, which can reduce signaling that normally limits muscle growth.
Is Follistatin-344 FDA-approved?
No. Follistatin-344 is not FDA-approved for muscle growth, body recomposition, muscular dystrophy, inclusion body myositis, anti-aging, recovery, or any other use.
Is Follistatin-344 the same as follistatin?
Not exactly. Follistatin is the naturally occurring protein. Follistatin-344 usually refers to a gene/transcript form or research construct used to produce follistatin activity.
Is Follistatin-344 the same as FST315?
Not exactly. FS344 is often discussed as the transgene form used to produce the FST315 protein isoform. FST315 is the circulating protein isoform.
Does Follistatin-344 build muscle?
Follistatin biology can increase muscle mass in animal models and gene-transfer research. Strong evidence for safe consumer muscle-building use in humans is lacking.
Does Follistatin-344 treat muscular dystrophy?
Follistatin gene therapy has been studied in Becker muscular dystrophy and Duchenne muscular dystrophy research contexts, but Follistatin-344 is not an FDA-approved treatment.
Does Follistatin-344 treat inclusion body myositis?
A small study reported promise for follistatin gene therapy in sporadic inclusion body myositis, but the strength of those claims has been challenged. It is not an approved treatment.
Is Follistatin-344 safe?
There is not enough human safety evidence to call Follistatin-344 safe for consumer use. Risks include immune reactions, pathway disruption, gene-transfer uncertainty, product mislabeling, contamination, and unknown long-term effects.
Are online Follistatin-344 products reliable?
No. Testing of black-market Follistatin-344 products found that many did not contain the claimed protein.
Is Follistatin-344 legal?
Follistatin-344 is not an FDA-approved drug. Online sale as a research peptide does not mean it is legally marketed for human therapeutic or enhancement use.
Is Follistatin-344 banned in sports?
Yes. WADA prohibits myostatin inhibitors, including myostatin-binding proteins such as follistatin.
Why do sellers call Follistatin-344 “research use only”?
Sellers often use “research use only” language because Follistatin-344 is not FDA-approved for consumer therapeutic use. The phrase does not make the product safe, legal, approved, or clinically proven.
What is the biggest risk with Follistatin-344?
The biggest risks are using an unapproved myostatin/activin-pathway modulator without adequate human safety data, relying on animal or small gene-therapy studies instead of approval-level evidence, buying mislabeled online products, and violating anti-doping rules.
Sources
- WADA: Prohibited List
- WADA: 2026 Prohibited List PDF
- WADA: Detection of Follistatin Doping in Urine and Blood
- USADA: WADA Prohibited List Guidance
- PMC: Follistatin Gene Delivery Enhances Muscle Growth and Strength in Nonhuman Primates
- PMC: A Phase 1/2a Follistatin Gene Therapy Trial for Becker Muscular Dystrophy
- PubMed: A Phase 1/2a Follistatin Gene Therapy Trial for Becker Muscular Dystrophy
- ClinicalTrials.gov: Follistatin Gene Transfer in Becker Muscular Dystrophy and Sporadic Inclusion Body Myositis
- ClinicalTrials.gov: AAV1.CMV.huFollistatin344 Trial in Duchenne Muscular Dystrophy
- PubMed: Follistatin Gene Therapy for Sporadic Inclusion Body Myositis
- PMC: Follistatin Gene Therapy for Sporadic Inclusion Body Myositis
- PubMed: Unfounded Claims of Improved Functional Outcomes Attributed to Follistatin Gene Therapy in Inclusion Body Myositis
- PMC: Unfounded Claims of Improved Functional Outcomes Attributed to Follistatin Gene Therapy in Inclusion Body Myositis
- PMC: Inhibition of Myostatin With Emphasis on Follistatin as a Therapy for Muscle Disease
- PubMed: Inhibition of Myostatin With Emphasis on Follistatin as a Therapy for Muscle Disease
- PMC: Long-term Enhancement of Skeletal Muscle Mass and Strength by Single Gene Administration of Myostatin Inhibitors
- PMC: Follistatin Improves Skeletal Muscle Healing After Injury and Disease Through an Interaction With Muscle Regeneration, Angiogenesis, and Fibrosis
- PubMed: Detection of Black Market Follistatin 344
- Wiley: Detection of Black Market Follistatin 344
- UniProt: Human Follistatin FST
Frequently asked questions
What is Follistatin-344?
Follistatin-344, also called FST-344 or FS344, is a follistatin gene/transcript form used in research and gene-transfer studies to increase follistatin activity.
What does Follistatin-344 do?
Follistatin-344 is used to increase follistatin activity. Follistatin binds and inhibits myostatin and activin, which can reduce signaling that normally limits muscle growth.
Is Follistatin-344 FDA-approved?
No. Follistatin-344 is not FDA-approved for muscle growth, body recomposition, muscular dystrophy, inclusion body myositis, anti-aging, recovery, or any other use.
Is Follistatin-344 the same as follistatin?
Not exactly. Follistatin is the naturally occurring protein. Follistatin-344 usually refers to a gene/transcript form or research construct used to produce follistatin activity.
Is Follistatin-344 the same as FST315?
Not exactly. FS344 is often discussed as the transgene form used to produce the FST315 protein isoform. FST315 is the circulating protein isoform.
Does Follistatin-344 build muscle?
Follistatin biology can increase muscle mass in animal models and gene-transfer research. Strong evidence for safe consumer muscle-building use in humans is lacking.
Does Follistatin-344 treat muscular dystrophy?
Follistatin gene therapy has been studied in Becker muscular dystrophy and Duchenne muscular dystrophy research contexts, but Follistatin-344 is not an FDA-approved treatment.
Is Follistatin-344 safe?
There is not enough human safety evidence to call Follistatin-344 safe for consumer use. Risks include immune reactions, pathway disruption, gene-transfer uncertainty, product mislabeling, contamination, and unknown long-term effects.
Are online Follistatin-344 products reliable?
No. Testing of black-market Follistatin-344 products found that many did not contain the claimed protein.
Is Follistatin-344 banned in sports?
Yes. WADA prohibits myostatin inhibitors, including myostatin-binding proteins such as follistatin.
Sources
- [1]WADA: Prohibited List
Anti Doping
- [2]WADA: 2026 Prohibited List PDF
Anti Doping
- [3]
- [4]USADA: WADA Prohibited List Guidance
Anti Doping
- [5]
- [6]
- [7]
- [8]
- [9]
- [10]
- [11]
- [12]
- [13]
- [14]
- [15]
- [16]
- [17]UniProt: Human Follistatin FST
Protein Reference
Last updated May 9, 2026