Verdict, decision matrix, deep dives, sourcing notes & full sources

Follistatin

Emerging Research

Myostatin Inhibitor | TGF-β Antagonist for Muscle Research | Peptide · Injectable

Aliases (6)

FST · FST-344 · FST-315 · ACE-083 · ACE-031 · FS344

TYPICAL DOSE

100-200 mcg (anecdotal only)

ROUTE

Subcutaneous injection

CYCLE

10-30 days

STORAGE

-20°C (lyophilized)

✎

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▸ Reconstitution Lyophilized peptide

Reconstitute lyophilized peptide with bacteriostatic water (BAC) using sterile technique. Calculator below converts vial mg + diluent mL into syringe units.

Steps

1 Wipe BAC water vial + peptide vial stoppers with isopropyl alcohol.
2 Draw the planned diluent volume into a 1 mL syringe.
3 Inject diluent slowly down the inside wall of the peptide vial — do NOT spray onto powder.
4 Swirl gently (do not shake) until fully dissolved. Solution should be clear.
5 Label vial with date reconstituted; refrigerate 2-8 °C.
6 Use within 30 days for most peptides (BPC-157 / TB-500 ~ 60 days at 4 °C).

Open dose calculator for Follistatin

▸ Overview TL;DR

Endogenous myostatin/activin trap with monster animal hypertrophy data but a graveyard of failed human trials (ACE-031 halted for cardiovascular safety, ACE-083 missed efficacy in FSHD/Becker MD). Peptide-vendor "follistatin" is almost certainly not bioactive intact full-length protein. SKIP at 20: theoretical cardiac hypertrophy + ovarian function risk, no real human upside data, sourcing is identity-fraud territory.

▸ Mechanism of action

Follistatin is a 32-39 kDa secreted glycoprotein (two main isoforms: FST-288 cell-surface bound, FST-315 circulating, plus the FST-344 prepropeptide that's been the gene-therapy target). It binds with high affinity to:

Myostatin (GDF-8) — the muscle-mass negative regulator. Knockout myostatin mice ("Schwarzenegger mice"), Belgian Blue cattle, and the documented German hypermuscular child all show what happens when myostatin is gone: 2-3x normal lean mass.
Activin A — broader TGF-β superfamily ligand involved in muscle, gonadal function (FSH regulation, ovarian folliculogenesis, spermatogenesis), and inflammation.

By acting as a soluble decoy that mops up these ligands before they reach ActRIIB (activin receptor type IIB), follistatin removes the natural ceiling on muscle growth. Downstream: reduced SMAD2/3 signaling → decreased atrogin-1/MuRF1 (muscle wasting genes) → net protein synthesis favors hypertrophy.

The Acceleron drugs are conceptually similar but mechanistically distinct:

ACE-031 = soluble ActRIIB-Fc fusion (decoy receptor, broader ligand binding than follistatin)
ACE-083 = locally-injected modified follistatin (FS-EEE-Fc) designed for muscle-localized action

Activin A binding is the hidden danger — that's why the side effect profile isn't just "more muscle."

▸ Pharmacokinetics No data

Pharmacokinetics data not available for this compound.

No half-life mentions found in the source notes.

▸Research indications2 use cases

Myostatin (GDF-8)

Most effective

the muscle-mass negative regulator. Knockout myostatin mice ("Schwarzenegger mice"), Belgian Blue cattle, and the documented German hyper…

Activin A

Effective

broader TGF-β superfamily ligand involved in muscle, gonadal function (FSH regulation, ovarian folliculogenesis, spermatogenesis), and in…

▸Quality indicators6 checks

✓

White, fluffy cake

Lyophilized powder should look uniform and matte before reconstitution.

✓

Clear after reconstitution

A correctly mixed solution is fully transparent — no haze or floaters.

✓

No discoloration

Yellow or brown tints suggest oxidation or degradation. Discard.

Slight clumping is OK

Some fine clumping pre-reconstitution is normal for hydroscopic peptides.

✓

COA available

HPLC purity ≥98% and mass-spec confirmation per batch is the gold standard.

⚠

Endotoxin tested

<0.5 EU/mg target. Not always tested by research-chem vendors — request it.

▸ What to expect Generic

1

Week 1

Injection / administration protocol established. Tolerability check.
2

Week 2-4

Early onset of effect — subtle in most users, noticeable in responders.
3

Week 4-8

Peak benefit window for most peptide cycles.
4

Week 8+

Cycle decision point: continue, taper, or break.

▸ Side effects + safety

Common (>10% in clinical trials): Nosebleeds, telangiectasias (skin spider veins), injection-site reactions for local delivery, transient muscle pain.
Less common (1-10%): Headache, fatigue, GI upset, joint pain.
Rare-serious (<1% but worth knowing):
- Cardiac hypertrophy concern — animal data suggests ActRIIB pathway blockade can drive pathological cardiac hypertrophy (the heart is muscle and responds to myostatin signaling). This was not definitively demonstrated in human trials but it's why the FDA + Acceleron program chose narrow indications.
- Vascular endothelial concerns — telangiectasias and nosebleeds suggest off-target action on vascular bed, possibly via BMP9/10 pathway interaction. Unknown long-term implications.
- Reproductive axis disruption — activin A regulates FSH secretion; chronic activin neutralization could theoretically suppress FSH → impaired spermatogenesis (males) or anovulation (females). Animal data shows this; human trials weren't long enough to rule it out.
- Tendon/connective-tissue mismatch — rapid muscle hypertrophy without proportional tendon adaptation = tear/strain risk. Documented in myostatin-knockout animal models.
Specific watch periods: First 4 weeks (vascular/nosebleed signal would emerge), 12 weeks (cardiac echo if used), 6 months (gonadal axis labs).

▸Interactions2 compounds

Other anabolic agents (AAS, SARMs, GH, IGF-1, MK-677):Avoid
Compound cardiac hypertrophy risk, compound tendon-mismatch risk, compound HPG suppression.
ARBs/ACE inhibitors:Avoid
Theoretical interaction via shared cardiac remodeling pathways — no human data but caution flag.

▸References6 sources