Follistatin 315
FS-315 / FST-315
A shorter isoform of follistatin with 315 amino acids that preferentially binds to muscle tissue rather than circulating systemically. More muscle-specific than FS-344, with potentially fewer off-target effects on reproductive hormones (activin/FSH axis). Considered safer for muscle-building applications due to reduced systemic myostatin inhibition.
Half-life
Shorter than FS-344 (tissue-bound)
Typical Dose
100 mcg/day
Route
subcutaneous
Category
growth_hormone
Evidence Overview
Strength of evidence across clinical, expert, and experimental lanes.
How Follistatin 315 is dosed in practice
Usually taken by subcutaneous (SubQ) injection. Typical range: 100 mcg/day. Half-life: Shorter than FS-344 (tissue-bound). Each card gives the dose, frequency and duration from one evidence lane: Clinical (human trials), Expert (practitioner protocols) or Experimental (early or animal data). These ranges describe what has been studied or used; they are not a prescription.
Work out the units to draw with the reconstitution calculator, how long a vial lasts with the vial duration calculator, and how levels fall between doses with the half-life calculator.
Less commonly used than FS-344 due to lower availability and higher cost. Theoretically preferred for muscle-specific myostatin inhibition without affecting reproductive hormones. Community data is sparse — most users default to FS-344 due to availability. Quality verification is even more difficult than FS-344.
- Comparative follistatin isoform research
- Advanced bodybuilding peptide community discussions
Unlock Full Evidence Sources
Get complete clinical data, expert protocols, and experimental research for Follistatin 315 and 90+ other compounds with Pro.
Upgrade to ProSafety & Contraindications
- Cancer history (growth factor modulation risk)
- Cardiac conditions
- Pregnancy or breastfeeding
- Very limited safety data — extreme caution
Follistatin 315: common questions
What is Follistatin 315?
A shorter isoform of follistatin with 315 amino acids that preferentially binds to muscle tissue rather than circulating systemically. More muscle-specific than FS-344, with potentially fewer off-target effects on reproductive hormones (activin/FSH axis). Considered safer for muscle-building applications due to reduced systemic myostatin inhibition.
How is Follistatin 315 dosed?
Follistatin 315 is usually taken by subcutaneous (SubQ) injection. Typical range in DoseCraft's library: 100 mcg/day. Experimental (early or animal data): 100 mcg daily SubQ; Once daily; 10–30 day cycles. These ranges describe what has been studied or used; they are not a prescription.
Is Follistatin 315 FDA-approved?
No. Follistatin 315 is not approved by the FDA for any use in people.
What is the half-life of Follistatin 315?
DoseCraft's library lists a half-life of Shorter than FS-344 (tissue-bound). Half-life sets how often a compound is dosed and how long it takes to clear: about five half-lives.
Who should not use Follistatin 315?
Listed contraindications: Cancer history (growth factor modulation risk); Cardiac conditions; Pregnancy or breastfeeding; Very limited safety data — extreme caution.
Information is for educational purposes only. Always consult a licensed healthcare provider before starting any peptide regimen.
Page updated . How we grade evidence: methodology.