Follistatin 315
Get a source-linked, educational explanation from this profile.
Complete Research Guide
Open each section for the available evidence. Gaps are stated rather than inferred.
Overview
Follistatin 315 is listed as myostatin inhibitor.
- •Muscle hypertrophy (research)
Regulatory status: Research chemical — WADA-banned.
Structure & Properties
Compound: Follistatin 315; also known as FS-315.
Pharmacologic class: Myostatin Inhibitor.
Known delivery routes: Subcutaneous.
Sequence, molecular weight, salt form, and excipient details are formulation-specific and are not listed unless verified by a manufacturer or laboratory COA.
How It Works
Circulating follistatin isoform with a heparin-binding domain removed; binds activin and myostatin systemically with a longer plasma residence than FS-344.
- •Systemic myostatin suppression
- •Lean-mass increase in animal models
Human Research
Evidence grade: Pre-clinical / Observational
Evidence is primarily preclinical or observational; human effectiveness and long-term safety are not established.
Laboratory Research
Animal gene-therapy and protein data
Preclinical findings describe biological plausibility, not proven benefit in people. Animal and laboratory doses do not translate directly to human use.
Processing & Interactions
Timing and exposure
No strict time-of-day requirement. Dose consistently at the same time daily and rotate injection sites. Follow the per-peptide dosing section above.
Potential interactions and combinations to avoid
- •Avoid stacking with peptides that share the same receptor or mechanism without clinical guidance.
- •Avoid combining with alcohol or immunosuppressants unless cleared by a clinician.
Absorption, half-life, metabolism, and clearance can vary by formulation and route. Use prescribing information when an approved product exists.
Safety & Precautions
Known or reported risks
- •Unknown effects on ovarian/pituitary activin signaling
- •Possible fibrosis
- •Purity concerns
Contraindications
- •Active malignancy
- •Pregnancy or fertility treatment
- •Endocrine disorders
- •History of any solid tumor or hematologic malignancy
- •Bleeding disorders, epistaxis, or anticoagulant/antiplatelet therapy (telangiectasia risk)
- •Cardiac hypertrophy, cardiomyopathy, or valvular disease
- •Pre-existing tendon or ligament pathology (strength gain outpaces connective-tissue adaptation)
- •Bleeding disorders or anticoagulant therapy without physician guidance (injection-site haematoma)
- •Active skin infection, cellulitis, or lipohypertrophy at intended injection sites
- •Inability to maintain sterile technique or safe sharps disposal
- •Not FDA-approved for human therapeutic use — no verified purity, sterility, or potency standards
- •Immunocompromised or transplant patients (unverified sterility and immunogenicity risk)
- •Concurrent participation in drug-tested sport (WADA prohibited or non-cleared substance)
- •Known hypersensitivity or prior reaction to this compound or any excipient/diluent
- •Pregnancy, attempting conception, or breastfeeding unless prescribed and monitored by a physician
- •Children and adolescents with open growth plates (unless under specialist endocrine care)
- •Active or recently treated malignancy without oncology clearance
- •Use without a confirmed diagnosis, baseline labs, and licensed clinical supervision
Unknown long-term toxicity should be assumed where controlled human data are limited. Seek urgent care for a severe or unexpected reaction.
Administration & Studied Formulations
Reference range: 100 mcg/day (reported research use)
Frequency: Daily for 10–30 days
Cycling: Short 10–30 day blocks reported; long-term use uncharacterized.
Subcutaneous (SubQ)
Default route for most research and therapeutic peptides — best absorption for reconstituted powder.
31G × 5/16" insulin syringe (U-100). 100 units = 1 mL. Pinch skin at abdomen (2" from navel), outer thigh, or love handle. Insert at 45–90°. Rotate sites daily to prevent lipohypertrophy. Alcohol-swab site, air-dry, inject slow, hold 5 sec.
Dosing information is educational context, not a personal recommendation. Approved products must follow their label and prescriber instructions.
Applications & Related Therapies
Potentially complementary measures
- •Most peptides pair safely with baseline nutrition, sleep, and resistance training.
Clinical use should account for diagnosis, approved alternatives, nutrition, activity, sleep, rehabilitation, current medicines, and appropriate monitoring.
Cases, Considerations & Ethics
Decision framework: establish the clinical goal, confirm evidence quality and legal status, screen contraindications and interactions, compare approved alternatives, define monitoring and stopping criteria, and use shared decision-making with a licensed clinician.
Case evidence: individual reports cannot establish safety or effectiveness and should not outweigh controlled trials.
Ethics: informed consent should distinguish established care from experimental use, disclose uncertainty and cost, avoid overstated claims, and never substitute research products for medically necessary care.
What is Follistatin 315?
In plain words
FS-315 is a form of a protein the body naturally makes. It travels in the blood and traps certain proteins that help control muscle growth and hormone activity. Researchers study whether this action could increase muscle size, but evidence is largely from laboratory and animal research, with limited human observations. Human safety is not established, including its effects on reproductive hormones, and research products may have purity problems.
Technical definition
Follistatin 315 (FS-315) is a circulating, 315-amino-acid glycoprotein isoform of endogenous follistatin, produced by cleavage of the signal peptide from the 344-amino-acid precursor. It retains a heparin-binding domain but has relatively low cell-surface affinity; it binds activins and myostatin, preventing their engagement with receptors and reducing downstream signaling. Experimental FS-315 is not FDA-approved for therapeutic use, and follistatin is prohibited by WADA.
Function
Dosing
Recommended Time of Day
Post-workout on training days.
See “Timing & Interactions” below for full fasted/fed circumstances, what to avoid combining, and what pairs well.
Administration & Technique
Injection & Application Sites
- Abdomen — 2 in (5 cm) away from the navel, either side. Fastest, most consistent SubQ absorption.
- Flank / love handle — Lateral fat pad above the hip. Good rotation site when the abdomen is tender.
- Outer thigh — Upper outer quadrant, a hand-width below the hip. SubQ pinch at 45°.
Diagram is a general illustration, not a medical instruction. Rotate sites every injection, keep 1 in (2.5 cm) between recent sites, and avoid scars, moles, bruises and the navel area.
Cycling
Short 10–30 day blocks reported; long-term use uncharacterized.
Timing & Interactions
- ·Avoid stacking with peptides that share the same receptor or mechanism without clinical guidance.
- ·Avoid combining with alcohol or immunosuppressants unless cleared by a clinician.
- ·Most peptides pair safely with baseline nutrition, sleep, and resistance training.
Storage & Reconstitution
Reconstitution Calculator
1 mL = 100 units on a standard U-100 insulin syringe. Draw to the nearest 0.5 unit and confirm dosing with a clinician before injection.
Your Notes
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Benefits
- ·Systemic myostatin suppression
- ·Lean-mass increase in animal models
Risks
- ·Unknown effects on ovarian/pituitary activin signaling
- ·Possible fibrosis
- ·Purity concerns
Contraindications
- ·Active malignancy
- ·Pregnancy or fertility treatment
- ·Endocrine disorders
- ·History of any solid tumor or hematologic malignancy
- ·Bleeding disorders, epistaxis, or anticoagulant/antiplatelet therapy (telangiectasia risk)
- ·Cardiac hypertrophy, cardiomyopathy, or valvular disease
- ·Pre-existing tendon or ligament pathology (strength gain outpaces connective-tissue adaptation)
- ·Bleeding disorders or anticoagulant therapy without physician guidance (injection-site haematoma)
- ·Active skin infection, cellulitis, or lipohypertrophy at intended injection sites
- ·Inability to maintain sterile technique or safe sharps disposal
- ·Not FDA-approved for human therapeutic use — no verified purity, sterility, or potency standards
- ·Immunocompromised or transplant patients (unverified sterility and immunogenicity risk)
- ·Concurrent participation in drug-tested sport (WADA prohibited or non-cleared substance)
- ·Known hypersensitivity or prior reaction to this compound or any excipient/diluent
- ·Pregnancy, attempting conception, or breastfeeding unless prescribed and monitored by a physician
- ·Children and adolescents with open growth plates (unless under specialist endocrine care)
- ·Active or recently treated malignancy without oncology clearance
- ·Use without a confirmed diagnosis, baseline labs, and licensed clinical supervision
Regulatory
Research chemical — WADA-banned
Veterinary Use (Pets)
No established veterinary protocol for Follistatin 315. Consult a licensed veterinarian before considering off-label use in any species.
Full veterinary reference →Functional Groups
Cited Works
Tap any study to open the published work.