Follistatin-344
Also known as: FS-344 · Follistatin · ACE-031
Contents
MW
38007 Da
Amino Acids
344 AA
Half-Life
4-6 hours
Route
SubQ, IM
Mechanism of Action
Follistatin-344 is a 344-amino acid glycoprotein that functions as a potent inhibitor of myostatin (GDF-8) and activin A — both TGF-β superfamily members that act as endogenous brakes on muscle growth.
PRIMARY MECHANISM — MYOSTATIN NEUTRALIZATION: Binds circulating myostatin with high affinity, preventing it from activating ActRIIB (activin receptor type IIB) on muscle cells. Myostatin signaling normally limits satellite cell activation, protein synthesis, and muscle hypertrophy. By removing this brake, follistatin allows unopposed muscle growth — the same principle behind the "double muscling" phenotype in myostatin-null animals.
ACTIVIN A INHIBITION: Also neutralizes activin A, which has overlapping anti-myogenic effects with myostatin. Additionally, activin A stimulates FSH (follicle-stimulating hormone) — so follistatin also suppresses FSH, with potential reproductive implications.
GENE THERAPY CONTEXT: Most clinical data comes from AAV (adeno-associated virus) gene therapy delivering FS-344 — a fundamentally different approach than injectable protein. The Mendell 2015 Phase 1/2a BMD trial used AAV-FS344 intramuscular injection, not circulating protein.
Dosing Protocol
Low Dose
███ – ███ mcg/day
Standard Dose
███ mcg/day
High Dose
███ – ███ mcg/day
Dosing protocols are for paid members
Get exact dosing ranges, injection frequency, timing rationale, and reconstitution math.
Get Clinical Access — $79/moFrequency
Daily SubQ.
Half-Life
4-6 hours
Reconstitution Guide
Full reconstitution protocol with BAC water volumes, concentration math, and units-to-draw per dose is available on the Clinical plan.
Unlock reconstitution guide →Clinical Warnings
FSH suppression may impair fertility.
Myostatin has cardiac protective roles — complete inhibition may affect the heart.
Injectable FS-344 pharmacokinetics poorly characterized vs gene therapy.
Extremely expensive.
Not FDA approved.
WADA prohibited.
Contraindications
Absolute
Active cancer
Pregnancy
Reproductive concerns
Relative Cautions
Hormone-sensitive conditions
Cardiovascular disease
Side Effect Profile
Mild
- ●Injection site reaction
- ●Mild fatigue
Moderate
- ●Joint pain
- ●Muscle cramping
- ●Headache
Severe (Rare)
- ●Potential tumor growth
- ●Reproductive effects
- ●Tendon rupture risk with rapid muscle gain
Synergistic Peptides
Common Stacks
IGF-1 LR3
CJC-1295
Research Status
SIGNIFICANT PRECLINICAL + EARLY HUMAN GENE THERAPY. PMID 18334646 (Haidet 2008 PNAS): AAV FS-344 in mice, sustained muscle mass increase for 2+ years. PMID 20368179 (Kota 2009 Sci Trans Med): Nonhuman primate safety + efficacy. PMID 26296241 (Mendell 2015): Phase 1/2a BMD gene therapy, 2 patients improved 58 and 125m on 6MWT. Note: gene therapy ≠ injectable protein.
Frequently Asked Questions
How does Follistatin-344 work?
Follistatin-344 is a 344-amino acid glycoprotein that functions as a potent inhibitor of myostatin (GDF-8) and activin A — both TGF-β superfamily members that act as endogenous brakes on muscle growth. PRIMARY MECHANISM — MYOSTATIN NEUTRALIZATION: Binds circulating myostatin with high affinity, preventing it from activating ActRIIB (activin receptor type IIB) on muscle cells. Myostatin signaling normally limits satellite cell activation, protein synthesis, and muscle hypertrophy. By removing th
What is the standard dose of Follistatin-344?
Follistatin-344 dosing protocols are available with a ClinPep Clinical subscription. Dosing varies by indication and patient factors — consult a licensed healthcare provider. General frequency: Daily SubQ.
What is the half-life of Follistatin-344?
The half-life of Follistatin-344 is 4-6 hours. This determines optimal dosing frequency and timing.
Who should not use Follistatin-344?
Follistatin-344 is absolutely contraindicated in: Active cancer; Pregnancy; Reproductive concerns. Use with caution in: Hormone-sensitive conditions; Cardiovascular disease.
What are the side effects of Follistatin-344?
Common mild side effects include: Injection site reaction, Mild fatigue. Moderate effects: Joint pain, Muscle cramping, Headache.
What peptides stack well with Follistatin-344?
Follistatin-344 is commonly stacked with: IGF-1 LR3, CJC-1295, BPC-157.
How do you reconstitute Follistatin-344?
Follistatin-344 is reconstituted with bacteriostatic water. Exact volumes, concentrations, and units-to-draw calculations are available in the ClinPep Clinical plan. Always follow your compounding pharmacy's instructions.
How long should you cycle Follistatin-344?
Follistatin-344 cycle protocols vary by indication. Detailed cycle length, on/off schedules, and monitoring guidelines are available with ClinPep Clinical access. Consult your healthcare provider for personalized cycling guidance.
References & Citations
10 PubMed studies · 3 clinical trials
Myostatin inhibitors in sarcopenia treatment: A comprehensive review of mechanisms, efficacy and future directions.
Samali Sahar Ahmad, Hosseini Seyede Fatemeh, Mohammadi Yaser, Sadri Farzad et al.. Molecular biology reports. 2025
Sarcopenia is a prevalent and debilitating skeletal muscle disorder in the aging population, characterized by progressive loss of muscle mass, strength, and function. Despite its significant impact on
Myostatin Function during In Vitro Myogenesis: Considerations for Knockout-Based Mechanistic Analysis.
Suh Joonho, Baik Jongmin, Lee Yun-Sil. Journal of bone metabolism. 2025
Myostatin (MSTN) is a well-known negative regulator of skeletal muscle growth, and its pharmacological blockade, such as with follistatin (FST), an endogenous MSTN inhibitor, is under active investiga
Apocynin Mitigates Diabetic Muscle Atrophy by Lowering Muscle Triglycerides and Oxidative Stress.
Sánchez-Duarte Sarai, Sánchez-Duarte Elizabeth, Sánchez-Briones Luis A, Meléndez-Herrera Esperanza et al.. International journal of molecular sciences. 2025
Diabetic muscular atrophy is a complication of diabetes mellitus that can decrease quality of life. Its complex mechanisms include alterations in proteolytic pathways, oxidative stress, and intracellu
The impact of weight loss on fat-free mass, muscle, bone and hematopoiesis health: Implications for emerging pharmacotherapies aiming at fat reduction and lean mass preservation.
Stefanakis Konstantinos, Kokkorakis Michail, Mantzoros Christos S. Metabolism: clinical and experimental. 2024
Similar to bariatric surgery, incretin receptor agonists have revolutionized the treatment of obesity, achieving up to 15-25 % weight loss in many patients, i.e., at a rate approaching that achie
Sarcopenia in the era of precision health: Toward personalized interventions for healthy longevity.
Chen Liang-Kung. Journal of the Chinese Medical Association : JCMA. 2024
Sarcopenia, characterized by the progressive loss of skeletal muscle mass and function, significantly impacts health outcomes in older adults. This review explores the evolving landscape of sarcopenia
Impact of Disease Severity and Disease-Modifying Therapies on Myostatin Levels in SMA Patients.
Mackels Laurane, Mariot Virginie, Buscemi Laura, Servais Laurent et al.. International journal of molecular sciences. 2024
Clinical trials with treatments inhibiting myostatin pathways to increase muscle mass are currently ongoing in spinal muscular atrophy. Given evidence of potential myostatin pathway downregulation in
A molecular pathway for cancer cachexia-induced muscle atrophy revealed at single-nucleus resolution.
Zhang Yichi, Dos Santos Matthieu, Huang Huocong, Chen Kenian et al.. Cell reports. 2024
Cancer cachexia is a prevalent and often fatal wasting condition that cannot be fully reversed with nutritional interventions. Muscle atrophy is a central component of the syndrome, but the mechanisms
Myostatin inhibitory peptides in sports drug testing.
Walpurgis Katja, Agricola Johannes, Thomas Andreas, Thevis Mario. Drug testing and analysis. 2023
Across species, skeletal muscle mass is negatively regulated by the TGF-β cytokine myostatin (MSTN). Inhibitors of this growth factor and its signaling pathways are therefore not only promising
Registered Clinical Trials
Interplay Between Interleukin-6 and Glucagon in the Regulation of Human Amino Acid and Protein Homeostasis
Effect of L-arginine on Microcirculation, Myogenesis and Angiogenesis Associated With Aging, Sarcopenia and Diabetes
Effect of Branch Chain Amino Acid Therapy on Sarcopenia in Children With Chronic Liver Disease.
Symptom Indications
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Complete Follistatin-344 Protocol
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This information is for educational and research reference purposes only. ClinPep does not provide medical advice, diagnosis, or treatment recommendations. All protocols should be reviewed by a licensed healthcare provider.