MEDICAL DISCLAIMER: Educational research guidelines only. Lyophilized peptides are investigational chemical compounds and are NOT approved for human consumption, diagnosis, or therapy. Consult a licensed physician before any research application.
Follistatin-315 Dosage Chart, Schedule & Reconstitution Protocol
Quickstart Highlights
Follistatin-315 (FS-315) is the main circulating isoform of follistatin, a glycoprotein that traps and neutralizes myostatin (GDF-8) and activin A, releasing the Smad2/3 brake on skeletal-muscle growth (PMID 20810712, PMID 19435857). Its acidic C-terminal tail keeps it soluble in blood rather than bound to cell surfaces like the shorter FS-288 isoform (PMID 15472207). The follistatin pathway is validated as a muscle target: AAV1-FS344 gene therapy improved walking distance in Becker muscular dystrophy patients (PMC4426808). However, no human trial has injected recombinant follistatin protein, and the molecule clears from circulation within hours, so there is no clinically validated subcutaneous dose. The community figure of about 100-300 mcg/day is unproven. Follistatin-315 is not FDA- or EMA-approved, is WADA-prohibited, and is sold for research use only; the dosing model here is educational, not medical advice.
Reconstitute: Add 1 mL bacteriostatic water → 1 mg/mL concentration.
Typical dose: 100-300 mcg/day SC (research only; no clinical dose)
Easy measuring: At 1 mg/mL, 1 unit = 0.01 mL = 0.0100 mg (10 mcg) on a U-100 insulin syringe.
Storage: Lyophilized powder stored frozen at −20 °C and protected from light; reconstituted solution refrigerated at 2-8 °C and used within about 2-4 weeks. Avoid repeated freeze-thaw cycles, which degrade the protein.
Half-life: Recombinant FS-315 protein clears in roughly a few hours (renal filtration, proteolysis, ligand-induced heparin clearance); only Fc-fusion follistatins reach day-long half-lives.
Route: Human follistatin therapy has only been intramuscular AAV gene transfer; the subcutaneous reconstitution here is an educational research model, not a clinical route.
Status: Not FDA- or EMA-approved; investigational/research use only; myostatin-pathway inhibitors are WADA-prohibited. Educational content, not medical advice.
About Follistatin-315
Follistatin-315 (FS-315) is the predominant circulating isoform of follistatin, a secreted glycoprotein that traps and neutralizes myostatin and activin A, two TGF-beta-family ligands that brake skeletal-muscle growth [1][2]. Because its acidic C-terminal tail keeps it from binding cell-surface heparan sulfate, FS-315 stays in the bloodstream rather than localizing to tissue, making it the form most associated with systemic, muscle-directed effects [3].\n\nImportant route note: there is no clinically validated injectable protein dose for follistatin in humans. The only human follistatin therapy to date used adeno-associated virus (AAV1-FS344) gene transfer delivered by intramuscular injection, not injected recombinant protein [7][8]. The subcutaneous reconstitution figures below are an educational research-modeling reference only, not a medical protocol.\n\nIn research and community settings, the discussed Follistatin-315 dosage is roughly 100-300 mcg per day subcutaneously, typically run in short cycles of about 10-30 days. This range has no clinical-trial backing. This guide models a 1 mg vial reconstituted with 1.0 mL of bacteriostatic water (1 mg/mL, 10 mcg per unit), so 100 mcg measures 10 units, 200 mcg measures 20 units, and 300 mcg measures 30 units on a U-100 insulin syringe.\n\nFrequency: Inject once daily subcutaneously. Follistatin-315 is not approved by the FDA or EMA and is presented here for educational purposes only, not as medical advice.
Quick Protocol Navigation
Reconstitution Instruction & Mixing Step-by-Step
Lyophilized powder must be reconstituted carefully. Agitating peptide chains can shear disulfide bonds and render the peptide biologically inert.
Draw 1.0 mL of bacteriostatic water into a sterile syringe (this yields a 1 mg/mL solution from a 1 mg Follistatin-315 vial — 10 mcg per insulin-syringe unit).
Inject the water slowly down the inner glass wall of the vial; aim away from the powder and do not spray the stream onto it, because follistatin is a fragile protein.
Gently swirl or roll the vial — never shake — until the solution is completely clear; foaming or vigorous agitation can denature the protein and reduce activity.
Store the reconstituted solution refrigerated at 2-8 °C and use within about 2-4 weeks; draw the research dose by units (100 mcg = 10 units, 200 mcg = 20 units, 300 mcg = 30 units on a U-100 syringe).
Educational note: there is no validated injectable protein dose for follistatin in humans — the only human follistatin therapy used AAV gene transfer, not injected peptide; swab the site, inject subcutaneously, and rotate sites if following this research model.
Interactive Follistatin-315 Syringe Calculator
Currently visualizing the 1 mg vial reconstituted with 1 mL bacteriostatic water. Adjust the target dose to dynamically render syringe units.
Reconstitution Calculation: 1mg dry powder in 1mL water yields 1.00 mg/mL. To evaluate a 250mcg dose, pull to 25.0 units (25 syringe ticks).
U-100 Syringe Representation
Educational reference visual. Assumes standard U-100 insulin syringe where 1.0 mL volume = 100 units.
Titration & Dose Escalation Schedules
| Phase | Dose per injection | Units (per injection) |
|---|---|---|
| Days 1-7 — conservative research start | 100 mcg | 10 units (0.10 mL) |
| Weeks 2-3 — common community range | 200 mcg | 20 units (0.20 mL) |
| Upper bound — reported research ceiling | 300 mcg | 30 units (0.30 mL) |
Administration guidelines: Refer to guidelines | 1 mL Reconstitution
Research Supplies Quantity Planner
Scientific mathematical planning of syringes, bacteriostatic water and dry vials needed for extended research blocks using the 1 mg vial.
Peptide Vials (Follistatin-315, 1 mg each):
- check8 weeks at 100 mcg/day ≈ 6 vials (5,600 mcg total)
- check12 weeks at 200 mcg/day ≈ 17 vials (16,800 mcg total)
- check16 weeks at 300 mcg/day ≈ 34 vials (33,600 mcg total) — the high vial count is why research cycles usually run only 10-30 days, not months
Insulin Syringes (U-100):
- checkOnce-daily dosing: 7 syringes per week
- check8 weeks ≈ 56 syringes; 12 weeks ≈ 84 syringes; 16 weeks ≈ 112 syringes
- checkEach dose draws only 10-30 units (100-300 mcg at 10 mcg/unit), well within one 1 mL syringe
Bacteriostatic Water (30 mL bottles): Use 1 mL per 1 mg vial for reconstitution.
- check8 weeks (~6 vials) ≈ 6 mL — under 1 bottle
- check12 weeks (~17 vials) ≈ 17 mL — about 1 bottle
- check16 weeks (~34 vials) ≈ 34 mL — 2 bottles; reconstitute only what you will use within ~2-4 weeks
Alcohol Swabs:
- check1-2 swabs per dose (vial top + injection site)
- check8 weeks ≈ 60-120 swabs; 12 weeks ≈ 90-170 swabs
- check16 weeks ≈ 120-230 swabs; keep extras for re-swabbing multi-use vials
Mechanism of Action (MOA)
Follistatin is an autocrine/paracrine glycoprotein built from an N-terminal domain plus three cysteine-rich follistatin domains (FSD1-3). Alternative splicing of the FST gene produces two principal precursors, FST317 and FST344; after the 29-residue signal peptide is removed, these mature into the secreted proteins FS-288 and FS-315 respectively. FS-315 carries a roughly 27-amino-acid acidic C-terminal extension that the shorter FS-288 lacks. That tail folds back over the basic heparin-binding sequence in FSD1, neutralizing it, so FS-315 has low affinity for cell-surface heparan-sulfate proteoglycans and circulates freely, making it the dominant follistatin isoform measured in human serum [2][3].\n\nFunctionally, follistatin is a high-affinity ligand trap for several TGF-beta superfamily proteins, most importantly myostatin (GDF-8) and activin A, and to a lesser extent GDF-11 and certain BMPs [1][2]. Two follistatin molecules wrap almost completely around a ligand dimer; the crystal structure of the activin:follistatin-315 complex (PDB 2P6A) shows follistatin simultaneously occluding both the type I and type II receptor-binding epitopes of the ligand, so the trapped myostatin or activin can no longer engage activin type II receptors (ActRIIB/ActRIIA) [4][5]. Blocking that engagement shuts down the Smad2/3 signaling cascade that normally suppresses myogenesis, releasing the brake on muscle protein accretion and satellite-cell activity [1][6].\n\nPharmacokinetics are the central caveat for any injectable use. Native and non-Fc recombinant follistatin protein is cleared from the circulation rapidly, on the order of a few hours, because of renal filtration, proteolysis, and, once it engages a ligand, activin-induced heparin binding that accelerates clearance of FS-315 complexes [4]. FS-315's acidic tail and glycosylation modestly slow clearance relative to the heparin-avid FS-288, but the protein still has a short systemic residence time; only engineered Fc-fusion follistatins achieve day-long half-lives, and those are different molecules. Consequently there is no pharmacokinetic basis for a standardized once-daily subcutaneous protein dose, and none has been validated in humans.\n\nDownstream, follistatin's myostatin/activin blockade is robustly anabolic in preclinical models: follistatin overexpression or injection increases muscle weight by roughly a third and acts through both satellite-cell proliferation and direct inhibition of myostatin and activin signaling [6]. The only human evidence comes from gene therapy: a Phase 1/2a trial delivered AAV1-FS344 (which encodes the FS-315 isoform) by intramuscular quadriceps injection to Becker muscular dystrophy patients and reported improved six-minute-walk distance and favorable muscle histology, with extended follow-up confirming durable ambulation gains in responders [7][8]. These results validate the follistatin pathway as a muscle target but do not establish a safe injectable protein dose, and Follistatin-315 remains an unapproved research compound.
Clinical Trial Efficacy Highlights
- starLee and colleagues (2010, Molecular Endocrinology) reviewed and extended work showing follistatin is a potent myostatin- and activin-binding protein: transgenic follistatin overexpression in mouse muscle produces dramatic hypertrophy, and combining follistatin overexpression with myostatin gene knockout quadruples muscle mass — far more than knocking out myostatin alone — implicating activin and other ligands beyond myostatin in follistatin's anabolic effect [1].
- starSidis and colleagues (2006, Endocrinology) directly compared follistatin isoforms and follistatin-like-3, demonstrating that FS-288, FS-303 and FS-315 differ chiefly in cell-surface (heparan-sulfate) binding rather than in their core ability to neutralize activin, myostatin and BMPs; FS-315's weak surface binding underlies its role as the soluble, circulating antagonist [2].
- starSchneyer and colleagues (2004, Journal of Clinical Endocrinology & Metabolism) developed an FS-315-specific immunoassay and showed FS-315 is the major follistatin isoform in human serum while being essentially undetectable in ovarian follicular fluid, confirming that the 315 isoform is the systemically circulating form and that cell-bound FS-288/FS-303 isoforms localize to tissues [3].
- starLerch, Shimasaki, Woodruff and Jardetzky (2007, Journal of Biological Chemistry) solved the structure and biophysics of heparin and activin binding to the follistatin isoforms, showing FS-315 inhibits activin like FS-288 but that activin binding can unmask heparin affinity in FS-315 — a mechanism that may accelerate clearance of circulating FS-315:ligand complexes [4].
- starThe crystal structure of the activin:follistatin-315 complex (RCSB PDB entry 2P6A) shows two follistatin molecules encircling the activin dimer and blocking both type I and type II receptor-binding surfaces, providing the structural basis for follistatin's antagonism of activin and myostatin signaling [5].
- starGilson and colleagues (2009, American Journal of Physiology-Endocrinology and Metabolism) showed in mice that local follistatin overexpression increased muscle weight by roughly 37%, an effect blunted to about 20% when satellite-cell proliferation was blocked by irradiation, demonstrating that follistatin-induced hypertrophy depends on both satellite-cell proliferation and combined inhibition of myostatin and activin [6].
- starMendell and colleagues (2015, Molecular Therapy) conducted a Phase 1/2a trial delivering AAV1-FS344 by bilateral intramuscular quadriceps injection in six Becker muscular dystrophy patients; four of six improved six-minute-walk distance (gains up to roughly 58-125 m) with reduced endomysial fibrosis and larger fibers on biopsy and no treatment-related adverse effects, the first gene-therapy trial to show functional improvement in any muscular dystrophy [7].
- starAl-Zaidy and colleagues (2015, Journal of Neuromuscular Diseases) reported extended follow-up of the same Becker cohort, finding a statistically significant average 11.5% improvement in six-minute-walk distance (p=0.02) sustained up to 12 months in the low-dose group, with non-responders being those who had extensive baseline muscle fibrosis [8].
Side Effects & Tolerability Profile
Clinical subjects transiently report mild side effects. Slowly escalating the titration dose represents the single most effective intervention to limit side effects.
- warningNo human safety data exist for injected follistatin protein. Every safety statement here is extrapolated from animal studies or from AAV gene-therapy trials that used a different delivery route, so the actual risk profile of subcutaneous FS-315 protein is genuinely unknown [7][8].
- warningFollistatin is a broad ligand trap, not a myostatin-only blocker — it also neutralizes activin A, GDF-11 and several BMPs. Systemic activin/BMP inhibition could disturb processes these ligands govern, including reproductive endocrinology, inflammation and wound healing, vascular tone, and bone morphogenesis [1][2].
- warningExcessive or sustained myostatin/activin inhibition is associated in animal models with tendon and connective-tissue changes and disproportionate muscle-to-tendon loading, raising a theoretical risk of tendon or ligament injury as muscle force outpaces connective-tissue adaptation.
- warningAs a recombinant glycoprotein, follistatin can provoke injection-site reactions and immunogenicity (anti-drug antibodies), which may cause local or systemic reactions and can neutralize activity; research-grade material also carries risks of endotoxin or contaminant exposure.
- warningActivin and follistatin signaling is implicated in cell proliferation and is dysregulated in several cancers; chronically manipulating this axis carries theoretical concerns about tumor promotion that have not been evaluated for exogenous FS-315.
- warningBecause FS-315 protein clears within hours, attempts to maintain an effect through frequent or high dosing simply increase cumulative exposure to an uncharacterized agent without any validated therapeutic window [4].
- warningIn the human gene-therapy trials no treatment-related serious adverse events were reported, but those used intramuscular AAV vector at controlled doses under medical oversight; this does not establish safety for self-administered subcutaneous protein [7][8].
- warningRegulatory/research status: Follistatin-315 is not approved by the FDA or EMA for any indication, is not a dietary supplement, and myostatin-pathway inhibitors are prohibited in sport by WADA. It is sold for laboratory research only, and this page is educational, not medical advice.
Subcutaneous Injection Technique
Most research peptides require subcutaneous injection into fatty tissue. Never inject directly into a blood vessel or deep muscle tissue unless clinically detailed.
1. Site Selection
Common locations include the abdomen (2 inches from navel), outer upper arms, or thighs.
2. Sanitization
Thoroughly clean the selected site, stopper and vial top using 70% isopropyl alcohol prep swabs.
3. Angle & Push
Pinch the skin and insert the needle at a 45 to 90-degree angle. Depress plunger smoothly.
4. Site Rotation
Rotate injection sites continuously to avoid lipodystrophy or tissue scarring.
Frequently Asked Questions
What is the typical Follistatin-315 dosage?expand_more
There is no clinically established Follistatin-315 dosage. No human trial has injected recombinant follistatin protein; the only human follistatin therapy used AAV1-FS344 gene transfer at vector (not protein) doses. In research and community discussion the figure cited is roughly 100-300 mcg per day subcutaneously, usually in short cycles of about 10-30 days, but this range has no clinical validation and no established safe ceiling. The reconstitution math on this page (a 1 mg vial in 1.0 mL of bacteriostatic water = 10 mcg per insulin-syringe unit) is an educational reference only, not a recommendation.
Is Follistatin-315 FDA approved?expand_more
No. Follistatin-315 is not approved by the FDA or the EMA for any indication, and no recombinant follistatin protein product is licensed for human use. Follistatin gene therapy has only been studied in early-phase clinical trials and remains investigational. Myostatin-pathway inhibitors are also on the WADA Prohibited List for athletes. Follistatin-315 is sold strictly for laboratory research, and the information here is educational and not medical advice.
How do you reconstitute Follistatin-315?expand_more
For the educational model on this page, draw 1.0 mL of bacteriostatic water into a sterile syringe and inject it slowly down the inner wall of a 1 mg Follistatin-315 vial, aiming away from the powder. Swirl or roll gently — never shake, because follistatin is a fragile protein that foaming can denature. The result is 1 mg/mL, or 10 mcg per unit on a U-100 syringe, so 100 mcg is 10 units and 300 mcg is 30 units. Store refrigerated at 2-8 °C and use within about 2-4 weeks.
What is the half-life of Follistatin-315?expand_more
Native and non-Fc recombinant follistatin protein clears from the bloodstream quickly — on the order of a few hours — through renal filtration, proteolysis, and ligand-induced heparin binding that speeds clearance of FS-315 complexes. The acidic C-terminal tail and glycosylation slow clearance only modestly versus the heparin-avid FS-288 isoform. Only engineered follistatin-Fc fusion proteins reach day-long half-lives, and those are distinct molecules. This short residence time is one reason there is no validated once-daily protein dosing protocol.
How is Follistatin-315 different from Follistatin-344, and can it be stacked?expand_more
They describe the same isoform at different stages: FST344 is the splice variant/precursor, and after its 29-amino-acid signal peptide is cleaved it becomes the mature, secreted 315-residue protein, FS-315. Research vendors label vials as 'Follistatin 344' or 'Follistatin 315' largely interchangeably. In community practice follistatin is sometimes paired with GH secretagogues or other anabolics, but there is no controlled safety or efficacy data for any follistatin stack, so combinations should be regarded as purely experimental.
Related Guides & Tools
Step-by-step references for reconstituting, measuring, and storing Follistatin-315, plus the universal dosing calculator.
Academic References & Study Citations
Lee SJ, Lee YS, Zimmers TA, et al. Regulation of muscle mass by follistatin and activins. Mol Endocrinol. 2010;24(10):1998-2008. View Scientific Paper →
Sidis Y, Mukherjee A, Keutmann H, et al. Biological activity of follistatin isoforms and follistatin-like-3 is dependent on differential cell surface binding and specificity for activin, myostatin, and bone morphogenetic proteins. Endocrinology. 2006;147(7):3586-3597. View Scientific Paper →
Schneyer AL, Wang Q, Sidis Y, Sluss PM. Differential distribution of follistatin isoforms: application of a new FS315-specific immunoassay. J Clin Endocrinol Metab. 2004;89(10):5067-5075. View Scientific Paper →
Lerch TF, Shimasaki S, Woodruff TK, Jardetzky TS. Structural and biophysical coupling of heparin and activin binding to follistatin isoform functions. J Biol Chem. 2007;282(21):15930-15939. View Scientific Paper →
The structure of the Activin:Follistatin-315 complex. RCSB Protein Data Bank, PDB ID 2P6A (2007). View Scientific Paper →
Gilson H, Schakman O, Kalista S, Lause P, Tsuchida K, Thissen JP. Follistatin induces muscle hypertrophy through satellite cell proliferation and inhibition of both myostatin and activin. Am J Physiol Endocrinol Metab. 2009;297(1):E157-E164. View Scientific Paper →
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. View Scientific Paper →
Al-Zaidy SA, Sahenk Z, Rodino-Klapac LR, Kaspar B, Mendell JR. Follistatin gene therapy improves ambulation in Becker muscular dystrophy. J Neuromuscul Dis. 2015;2(3):185-192. View Scientific Paper →