Follistatin

Follistatin is an endogenous protein that binds and neutralizes myostatin and activin A — both negative regulators of muscle growth. The two most-discussed research forms are Follistatin-344 and Follistatin-315, distinguished by their C-terminal length and tissue affinity. The shorter Follistatin-315 circulates more freely in serum, while Follistatin-344 binds more tightly to cell surfaces. Both are studied as potential muscle-growth and anti-fibrotic agents. They are sold strictly for laboratory research.

Your body has a built-in brake on muscle growth called myostatin. Follistatin is the body's own brake-release: it binds myostatin and removes it from circulation, allowing muscles to grow more freely. Famous cases of natural myostatin or follistatin variation — like the 'super-muscular' Belgian Blue cattle or rare humans with myostatin mutations — show how dramatic this pathway can be. Follistatin is one of the most-discussed compounds in muscle-growth research.

Follistatin binds myostatin and activin A with high affinity, preventing them from engaging their receptors (ActRIIB) on muscle cells. With the inhibitory signal blocked, downstream Smad2/3 signaling drops and the AKT/mTOR muscle-growth pathway is allowed to operate at higher capacity. Follistatin-344 has stronger heparan-sulfate binding and tends to act more locally; Follistatin-315 circulates more broadly.

Powerful glycoprotein. Temporarily blocks myostatin — the body's genetic 'brake' on muscle growth.

1. Follistatin
2. IGF-1 / myostatin-axis receptors
3. Satellite-cell activation and protein-synthesis signalling
4. Hypertrophy and tissue-remodelling endpoints

A plain-English read on how much published evidence currently exists for Follistatin. These ratings describe the volume and maturity of the literature — not effectiveness, safety, or suitability for any use.

Current limitations: most compounds in this category are studied in preclinical or small-sample settings. Absence of large controlled human trials is the single biggest limitation to keep in mind when reading any summary of Follistatin.

Lyophilized compounds are supplied as a dry powder. Concentration is simply the total amount in the vial divided by the volume of bacteriostatic water added:

Concentration (mg/mL) = total mg in vial ÷ mL of diluent added

Commonly supplied vial sizes

1mg vial

Worked concentration example

1mg + 1mL BAC water → 1mg/mL On U-100 insulin syringe:

• • 10 units = 100mcg

Run your own numbers with the reconstitution calculator — it converts vial size and diluent volume into mg/mL and mcg/mL.

The figures below are reported here descriptively, because they are the values most frequently cited in publicly available research literature and reference material. They are not instructions, not a protocol, and not a recommendation. These compounds are supplied for laboratory research use only and are not approved by the FDA for human consumption.

Commonly cited amounts

100mcg daily subcutaneous for 10 days

Commonly cited frequency

Daily during 10-day cycle

Commonly cited study duration

10 days, then off

Peptides are supplied freeze-dried because peptide bonds degrade far faster in solution than in a dry state. Understanding storage is part of understanding why the powder form exists at all.

• •Lyophilized powder: stored refrigerated, typically stable for months to years.
• •Reconstituted solution: refrigerated at 2–8°C, generally discussed as stable for roughly 30–60 days.
• •Heat and direct light accelerate degradation — vials are kept cool and dark.
• •Reconstituted material is not re-frozen; ice crystal formation disrupts peptide structure.
• •Bacteriostatic water contains 0.9% benzyl alcohol as a preservative, which is what allows multi-day storage after reconstitution.

More detail in the storage & handling guide and how peptide quality is evaluated.

• •Muscular dystrophy gene therapy (AAV-follistatin)
• •Inclusion body myositis trials
• •Sarcopenia and age-related muscle loss
• •Fibrosis research (anti-activin effects)
• •Comparative myostatin-pathway pharmacology

Follistatin is a perennial topic on bodybuilding and biohacking forums, often alongside ACE-031 and YK-11 in 'myostatin inhibitor' discussions. Most online debate concerns whether grey-market 'Follistatin-344' is real, properly folded protein — synthesizing a 344-residue protein with correct disulfide structure is far more difficult than producing a small peptide. Reports vary wildly, and quality is a major concern.

“The body's own muscle-brake release.”

Follistatin is sometimes paired with ACE-031 in theoretical myostatin-pathway stacks, with GH-secretagogue protocols (CJC-1295 + ipamorelin) for independent pathway combination, or with BPC-157 in recovery contexts. None of these are clinically validated combinations.

Follistatin is an endogenous myostatin- and activin-binding protein studied for muscle growth, anti-fibrotic effects, and muscular dystrophy gene therapy. Research-grade Follistatin-344 and -315 are sold for laboratory use only, with significant concerns about quality and folding in the grey market.