Follistatin 344
Follistatin isoform FST-344 · FST-344 · FS-344 · Follistatin · FST344
Activin- and myostatin-binding protein run in short daily courses; data are animal-only.
Typical dose
100 mcg
Once daily
Range
50–200
mcg
Half-life
1 h
see Dosing
Evidence
Animal only
Subcutaneous · Intramuscular
What it is
Follistatin is a naturally occurring glycoprotein that binds and neutralises members of the TGF-beta superfamily, most relevantly myostatin and activin A. FST-344 refers to the 344-amino-acid precursor transcript; after the signal peptide is cleaved, the secreted product is the 315-residue circulating isoform, so what is in the vial is a full protein, not a short peptide.
The interest in bodybuilding comes from genetics rather than from trials. Animals engineered to overexpress follistatin, or to lack myostatin, develop dramatic muscle hypertrophy, and follistatin blocks more than one negative regulator, so it produces larger effects in mice than myostatin antibodies do.
What does not translate is the delivery. The human trials that showed real functional gains used AAV gene therapy injected directly into muscle, giving sustained local expression. Injecting the recombinant protein subcutaneously for a couple of weeks is a fundamentally different exposure, and there is no human data showing it works. Grey-market follistatin is also one of the hardest products to make correctly, so misidentification and inactive product are common.
How it works
Myostatin and activin A signal through activin type II receptors to suppress muscle growth, holding a brake on satellite cell proliferation and protein synthesis. Follistatin binds these ligands directly in the extracellular space, sequestering them before they can reach their receptors, which releases the brake and allows both fibre hypertrophy and satellite cell expansion.
Because follistatin traps multiple ligands rather than just myostatin, it has broader effects than selective myostatin inhibitors. That also means it touches the activin-inhibin axis, which regulates FSH, so it is not a muscle-only intervention.
Dosing
The short-course convention is driven by cost and clearance, not by evidence of a safe ceiling. Nobody has established a dose-response curve for injected recombinant follistatin in humans, so any number here is community practice.
Reconstitution calculator
Pre-loaded with Follistatin 344’s vial size, water volume and typical dose. Change anything.
Typical: 100 mcg · range 50–200
Draw to
10 u
0.1 mL · 100 mcg
Concentration
1 mg/mL
10 mcg per unit
Doses per vial
10
Vial lasts
10 days
Draw to 10 units on the barrel.
Once mixed
Refrigerate at 2-8C and use within 7-10 days. Proteins of this size lose activity in solution faster than short peptides, so short courses should be reconstituted in small batches.
1 mL of bacteriostatic water into a 1 mg vial gives 1000 mcg/mL, so 100 mcg is 10 units on a U-100 insulin syringe. This is a folded, glycosylated protein rather than a short peptide: add the water slowly down the vial wall, swirl until clear, and never shake or vortex.
Storage
Before mixing
Keep frozen at -20C or below, where it is stable for around 12 months; avoid repeated freeze-thaw of the dry vial.
After mixing
Refrigerate at 2-8C and use within 7-10 days. Proteins of this size lose activity in solution faster than short peptides, so short courses should be reconstituted in small batches.
Reported benefits
- ▪Binds and neutralises myostatin, removing a brake on muscle growth
- ▪Also traps activin A, giving broader inhibition than myostatin-only agents
- ▪Produces marked hypertrophy and satellite cell expansion in animal models
- ▪Gene-therapy delivery improved six-minute walk distance in small human muscle-disease trials
- ▪No androgenic activity and no HPTA suppression
- ▪Effects appear to include both fibre hypertrophy and increased fibre number in rodents
Side effects
- ▪Injection-site pain, redness and swelling, common with recombinant proteins
- ▪Possible antibody formation against the injected protein, which can neutralise it
- ▪Disruption of the activin-inhibin axis, with potential effects on FSH and fertility
- ▪Systemic activin blockade has been linked to vascular and bleeding effects for this drug class
- ▪Unknown long-term consequence of suppressing a tumour-suppressive signalling pathway
- ▪High rate of misidentified, inactive or bacterially contaminated grey-market product
Do not use if
- ▪Active or previous cancer, since myostatin and activin signalling is growth-suppressive
- ▪Pregnancy, breastfeeding, or active fertility treatment
- ▪Known bleeding disorder or anticoagulant therapy
- ▪Any autoimmune condition where an added protein antigen is undesirable
Evidence level — Animal only
Preclinical animal data — no meaningful human trials.
Not approved as a drug anywhere; sold only as a research-grade recombinant protein and prohibited in sport under the WADA code.
Commonly run with
HGH
Recombinant human growth hormone, the reference compound every GH peptide tries to imitate.
2 IU · Once daily, split into two injections above about 4 IU
IGF-1 LR3
Modified IGF-1 that evades its binding proteins, making it far more potent than the native hormone.
40 mcg · Once daily
MK-677
Oral ghrelin mimetic that raises GH and IGF-1 for a full 24 hours from one daily dose.
10 mg · Once daily
Follistatin 344 FAQ
Does injecting follistatin actually build muscle in humans?+
There is no human evidence that the injected recombinant protein does. The positive human results came from AAV gene therapy delivered into the muscle, which produces sustained local expression rather than an hour-long systemic spike.
Why is the cycle only 10-30 days?+
Cost and clearance, not a safety threshold. Daily dosing of a protein that clears in about an hour burns through vials quickly, and there is no data establishing what a longer run does either way.
Follistatin or ACE-031?+
Both sit on the same axis. ACE-031 has actual human pharmacokinetics and a documented reason it was abandoned; follistatin has better animal results but no human data for the injectable form. Running both together doubles the unknowns on a pathway that also controls blood vessel maintenance and FSH.
Will it affect my hormones?+
Potentially. Follistatin binds activin, and activin drives FSH secretion, so meaningful systemic exposure could shift FSH and downstream reproductive signalling. This has not been characterised in men using it recreationally.
How do I know the vial contains real follistatin?+
You largely cannot without third-party testing. It is a 315-residue glycoprotein, far harder and more expensive to produce than a short peptide, which makes it one of the most commonly faked items on the grey market. A batch certificate of analysis from an independent lab is the only meaningful check.
References
- 1.Regulation of myostatin activity and muscle growth — Proceedings of the National Academy of Sciences (2001) PMID 11459935
- 2.Inhibition of myostatin with emphasis on follistatin as a therapy for muscle disease — Muscle & Nerve (2009) PMID 19208403
- 3.A Phase 1/2a Follistatin Gene Therapy Trial for Becker Muscular Dystrophy — Molecular Therapy (2015) PMID 25322757
- 4.Follistatin Gene Therapy for Sporadic Inclusion Body Myositis Improves Functional Outcomes — Molecular Therapy (2017) PMID 28279643
More growth factors
ACE-031
Myostatin and activin decoy receptor; human trials were halted over bleeding side effects.
1 mg · Once weekly
IGF-1 DES
Truncated IGF-1 analogue with roughly 10x potency and a 20-30 minute window of action.
100 mcg · Once daily
IGF-1 LR3
Modified IGF-1 that evades its binding proteins, making it far more potent than the native hormone.
40 mcg · Once daily
PEG-MGF
PEGylated IGF-1Ec E-peptide used after training to extend satellite-cell signalling.
200 mcg · 2x weekly