Follistatin 344 Dosage: Why the Human Evidence Is Gene Therapy

Follistatin 344 at a glance

What it is

A 38 kDa secreted glycoprotein, not a small peptide. UniProt P19883 annotates the human follistatin precursor as 344 residues with a molecular mass of 38,007, a signal peptide at residues 1-29 and a mature chain at 30-344 — so the secreted species is 315 residues long, and FS-344 names the precursor rather than the circulating protein

Researched for

Myostatin and activin inhibition, and through that skeletal-muscle mass — studied in Becker muscular dystrophy, inclusion body myositis, Duchenne models and facioscapulohumeral dystrophy models

Commonly reported range

Community-reported figures cluster around 100 mcg per administration. There is no trial dose to report because no published trial has injected follistatin protein into a human — the figures in circulation have no clinical study behind them, which is a different situation from a dose that is merely off-label

Route reported

Community protocols describe subcutaneous or intramuscular injection. The published human protocols describe something else entirely: direct intramuscular delivery of a viral vector carrying the FS344 gene into named muscles

Reported frequency

Daily in most community protocols. The gene-therapy trials dosed once, because a vector that transduces muscle keeps expressing

Reported cycle

Community protocols describe short runs of roughly 10 to 30 days. No trial supports any cycle length for injected protein

Plasma half-life

No published pharmacokinetic study of injected, unmodified follistatin in humans could be located. This page previously published an animal figure of 'roughly 90 minutes to a few hours' and that claim is RETRACTED — see the half-life section for what replaced it, and why the industry's own systemic candidate had to be re-engineered before it could be dosed at all

Regulatory status

Not an approved medicine in any jurisdiction, in either protein or gene-therapy form. Myostatin inhibitors and their mimetics are prohibited in sport under WADA class S4.4. Research use only

Reported ranges from research/community — examples, not recommendations.

What it is / mechanism

Follistatin binds activins and other TGF-beta family ligands — myostatin among them — and prevents them from signalling. Myostatin restrains skeletal-muscle growth, so a molecule that sequesters it is expected to increase muscle mass, and in animal models it does. The name is where the confusion starts, and it is worth resolving before anything else. UniProt's human follistatin entry, P19883, describes a 344-residue precursor of 38,007 Da whose first 29 residues are a signal peptide, cleaved during secretion, leaving a mature chain running from residue 30 to 344 — 315 residues. The gene-therapy literature says the same thing in its own vocabulary: the FS344 variant undergoes post-translational modification to FS315. Two independent sources, one conclusion — 344 is the length of the thing before secretion, and 315 is the length of the thing that circulates. A vial labelled 'Follistatin 344' is named after a precursor. The other number worth knowing is 288. FS288 is the isoform that stays bound to cell surfaces through heparan sulfate and carries high activin affinity; FS315 is the serum-based form with roughly ten-fold lower affinity for activin. That difference is not trivia — it is the reason FS344 was the variant selected for human work. Follistatin interacts with the pituitary activin-inhibin axis and suppresses follicle-stimulating hormone secretion, and the lower-affinity circulating isoform was chosen specifically to keep that endocrine effect in check. When a research programme picks an isoform to avoid an endocrine consequence, the consequence is real. One complication belongs here rather than in a footnote. A 2018 analysis in Nature Communications found that in muscle-wasting and atrophying diseases the myostatin pathway is already downregulated — myostatin and activin receptor expression fall while endogenous follistatin rises — and proposed this as an explanation for why several anti-myostatin drugs produced limited efficacy in clinical trials. The simple story, block myostatin and gain muscle, has been tested repeatedly in humans by pharmaceutical programmes with far better molecules than a research vial, and it has mostly underdelivered.

Researched effects

The honest summary is that follistatin's demonstrated functional benefits in humans and in disease models come from gene transfer, and the evidence for injected protein is absent rather than negative. The clinical landmark is a gene-transfer trial in Becker muscular dystrophy that delivered the FS344 isoform — the gene, packaged in adeno-associated virus, injected directly into muscle — and reported improved ambulation. The choice of isoform in that trial is the same choice described above: FS344 processing to FS315, with its lower activin affinity, to limit interference with the pituitary axis. The animal work points the same way. In a DUX4-driven model of facioscapulohumeral dystrophy, AAV1.Follistatin increased muscle mass and strength even while the toxic transgene was still being expressed. In aged mdx mice, follistatin delivered alongside micro-dystrophin restored force generation and resistance to contraction-induced injury in a way that neither treatment achieved alone. In limb-girdle models, plasmid-delivered human follistatin combined with alpha-sarcoglycan reduced membrane damage. Every one of those results was produced by putting the gene into muscle. What none of them establishes is what happens when you inject the protein. That is not a rhetorical point — it is the design problem the pharmaceutical industry ran into and solved differently. The systemic follistatin candidate developed for muscle wasting is not follistatin; it is FST-delta-HBS-Fc, a follistatin-315 mutant with its heparan-sulfate binding site deliberately disabled, fused to a human IgG4 Fc domain. Two separate pieces of engineering, both aimed at making the molecule survive in circulation long enough to act. The published pharmacokinetic work on that construct in mice and cynomolgus monkeys found clearance still driven by glycosylation, specifically sialic acid content, through the asialoglycoprotein receptor — to the point that the developers had to define sialylation specifications for the manufactured material. A research vial of unmodified follistatin-344 is the molecule that engineering was working around.

Dosage — reported ranges (overview)

There is no trial dose for injected follistatin protein, and that sentence is the single most important thing on this page. That is a stronger statement than 'off-label' or 'not approved'. Plenty of compounds in this library have doses that came from a trial and are used outside it. Here, no published trial has injected follistatin protein into a human at all. The figures that circulate — typically around 100 mcg per administration, given daily for ten to thirty days — trace to community protocols, not to a study. Nobody measured them against a control, nobody titrated them, and there is no published pharmacokinetic work on unmodified injected follistatin from which a sensible interval could even be derived. The human protocols that do exist describe a different intervention. They deliver the FS344 gene in a viral vector, injected directly into a target muscle, once. The muscle then expresses follistatin locally for as long as the transduced fibres keep expressing. A daily subcutaneous injection of protein is not a lower-tech version of that; it is a different route, a different tissue exposure, a different duration and a different molecule state. The frequency question follows from the same gap. Community protocols dose daily, and the usual justification is a short half-life — but the half-life figure most often quoted for this compound is one this page previously published and has now retracted, for reasons set out below. Daily dosing here is a convention that grew up around a number nobody sourced. None of this is a recommendation, and none of it is a protocol. It is a description of how much weight the numbers in circulation can carry, which is very little.

A printable protocol sheet with a reconstitution reference and an injection log comes with All-Access Lifetime.

Reconstitution — bac-water math

Research follistatin-344 is usually supplied as a 1 mg lyophilised vial, and the arithmetic below is worked on that. Concentration is the vial's contents divided by the millilitres of bacteriostatic water added. A 1 mg vial is 1,000 mcg, so 1 mL gives 1,000 mcg/mL. On a U-100 insulin syringe 100 units is 1 mL, so units to draw = dose in mcg divided by concentration in mcg/mL, times 100. A 100 mcg example at 1,000 mcg/mL is 100 / 1000 x 100 = 10 units. Ten units is a very small volume to measure accurately, and that points the opposite way from a milligram-dosed compound. With mazdutide or survodutide the risk is over-dilution pushing a dose past the syringe; here the risk is under-dilution making the mark unreadable. More diluent gives a bigger, more measurable draw for the same quantity — 2 mL puts a 100 mcg example at 20 units and 3 mL puts it at 30. One property specific to this molecule deserves a mention alongside the arithmetic: follistatin binds heparan sulfate, which is what the pharmaceutical Fc-fusion construct had to mutate away. That is a binding property of the protein, not a handling instruction, but it is a reminder that a 38 kDa glycoprotein is a more delicate object than a 10-residue peptide, and rough handling costs more. This is concentration math, not a dose.

This is concentration math, not a dose recommendation.

Injection / administration basics

'Where to inject follistatin 344' is a question this page gets asked, and it has an answer that is more useful than a site diagram. The published human protocols inject a viral vector carrying the follistatin gene directly into specific skeletal muscles — the muscle is the target because the point is to make that muscle express follistatin locally. In the preclinical plasmid work, intramuscular injection was followed by electroporation to drive the DNA into fibres. Site selection in those studies is a surgical and anatomical decision tied to which muscle the investigators wanted to treat. None of that transfers to injecting a protein. Community protocols describe subcutaneous or intramuscular administration, and there is no published study establishing a site, a depth, a volume or an interval for injected follistatin protein in humans, because there is no published study injecting it. An answer that named a site would be inventing one. What can be said is what the molecule is: a 38 kDa glycoprotein that binds heparan sulfate on cell surfaces and matrix, which is exactly the property a pharmaceutical developer removed by mutation before attempting systemic dosing. A protein with that behaviour does not distribute like a small peptide, and reasoning about it as though it does is the error underneath most of the protocols in circulation. Route and site are reported here as published study parameters. Nothing on this page is an administration instruction.

Half-life & frequency rationale

This section previously stated that follistatin 344 has 'a short half-life, with animal-model estimates ranging from roughly 90 minutes to a few hours', and that tissue binding extends the effect window. That claim is RETRACTED. It was published without a citation, and re-checking the literature did not produce a primary study supporting it for unmodified follistatin. Here is what the record does contain. No published pharmacokinetic study of injected, unmodified follistatin protein in humans could be located. The nearest published pharmacokinetics belong to FST-delta-HBS-Fc, and that molecule is follistatin-315 with its heparan-sulfate binding site disabled by mutation and an IgG4 Fc domain fused on — two modifications whose entire purpose is to change how long the molecule persists. Its clearance in mice and cynomolgus monkeys was driven by glycosylation, specifically sialic acid content, through the asialoglycoprotein receptor, to the degree that the developers set sialylation specifications on the manufactured material to control it. The inference that survives is qualitative rather than numeric, and it is the useful one: unmodified follistatin is not a molecule that persists well in circulation, which is why making a systemic follistatin drug required removing a binding site and adding an Fc domain. A specific half-life in minutes for the unmodified protein is not something this page can source, and it will not print one it cannot. If you see a figure quoted elsewhere, the useful question is which study measured it, in which species, on which construct.

Stacking — overview

The most cited follistatin result in the literature is a combination, and it is worth understanding what kind of combination it was. In aged mdx mice, follistatin delivered alongside micro-dystrophin restored force generation and resistance to contraction-induced injury when neither did so alone. In limb-girdle models, follistatin plus alpha-sarcoglycan reduced membrane damage. Those are gene-therapy combinations — two transgenes delivered into muscle — not two vials drawn into one syringe. The synergy demonstrated was between a gene that repairs a structural defect and a gene that enhances muscle mass, in an animal with that structural defect. None of that supports pairing injected follistatin protein with anything, and the market's usual suggestions in this class have a further problem: growth-hormone secretagogues and IGF-1 analogues act on a different axis entirely, so a stack combining them is an assumption stacked on an absence rather than a mechanism with evidence behind it.

For how combinations are grouped by research context, the named blends, and why a pre-mixed blend vial cannot be calculated from its total milligrams, see the peptide stacks guide.

Storage & handling

• Lyophilized (powder): store sealed and refrigerated at 2-8°C, protected from light and moisture; long-term storage is commonly at -20°C or below. Do not use past intended research shelf life.
• Reconstituted (liquid): refrigerate at 2-8°C, protect from light, and avoid freeze-thaw cycles and vigorous shaking. This matters more here than for a short peptide — follistatin is a 38 kDa glycoprotein, and larger glycoproteins are the sort of molecule that loses structure to repeated freezing and to foaming.
• Aliquot if a vial will be entered repeatedly. Bacteriostatic water's benzyl alcohol is a preservative for multi-dose entry, but it does not protect a protein from mechanical or thermal stress.
• Label the vial with the reconstitution date and the resulting concentration in mcg/mL. At 10-30 unit draws the concentration is doing all the work in the arithmetic, and it is the number nobody remembers later.

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