Follistatin-344
FS-344 · Follistatin 344
Myostatin is the body's brake on muscle growth. Animals and the rare humans who lack a functional myostatin gene are visibly, extraordinarily muscular, and that observation has driven twenty years of interest in blocking it pharmacologically. Follistatin is one of the body's natural myostatin inhibitors, and follistatin-344 is a form of it that has produced striking muscle growth in animals.
None of that has translated. No human trial of follistatin-344 as an injectable protein exists. The most advanced human work on this pathway used a different molecule entirely: gene therapy delivering follistatin, in a handful of muscular dystrophy patients. The most instructive human data comes from a related myostatin inhibitor, ACE-031, whose trials were stopped early after participants developed nosebleeds and dilated blood vessels in the skin. That happened because the activin pathway follistatin also blocks does more in the body than restrain muscle.
There is a practical problem on top of the biological one. Follistatin-344 is a 344-residue glycoprotein, an order of magnitude larger than the peptides sold beside it, and it needs mammalian cell expression and specific glycosylation to function at all. Producing it correctly is expensive and difficult, and it is not plausible that every vial sold cheaply as follistatin-344 contains correctly folded, glycosylated, biologically active protein. Much of the debate about dosing it assumes a premise nobody has established.
How it works
Follistatin binds and neutralises myostatin, releasing the brake on muscle growth. In animals this produces substantial increases in muscle mass, and the effect is robust across species.
It does not stop at myostatin. Follistatin also binds activin A and several other members of the TGF-beta family, which are involved in reproductive function, wound healing, inflammation and blood vessel regulation. That breadth is the source of the safety concern, and it is not hypothetical. The ACE-031 trials were halted for vascular effects consistent with exactly this off-target activity.
FS-344 is the gene-encoded precursor form, which cells process into the circulating FS-315 protein. What is sold under the name is not necessarily either of those in a functional state.
Local injection into a muscle is often described as a way to target growth. Follistatin is a secreted protein that enters circulation, and no human data supports the idea that injecting it in one place confines its effects there.
Regulatory status — United States
Not approved anywhere, and never studied in a human trial as an injectable protein. Follistatin gene therapy has been studied in small trials for muscular dystrophy. The most advanced pharmaceutical work on the myostatin pathway — using a different molecule — was halted for safety.
Last reviewed 16 Aug 2026. Regulatory positions in this category change frequently; we date this line so you can see how current it is.
What it is studied for
Each entry states the evidence behind it. We do not rank indications by effectiveness — for most compounds here, that would be a claim nobody can support.
Muscle growth
Published reviewThe reason it is bought.
EvidenceSubstantial muscle growth demonstrated in animals. No human trial of injected follistatin-344 has ever been conducted.
Muscular dystrophy
Clinical trialWhere the human work on this pathway actually sits.
EvidenceA small gene therapy trial delivering follistatin to muscle in Becker muscular dystrophy reported improved walking distance in some participants. That is gene therapy, not an injected protein.
Identity and clearance
Molecule
- Class
- Glycoprotein, TGF-beta family antagonist; the gene-encoded precursor form
- Molecular weight
- 37000 Da
- Length
- 344 amino acids
A folded, glycosylated protein, not a synthetic peptide. It cannot be made by the solid-phase synthesis that produces most compounds sold alongside it, which is the root of the authenticity question.
Dose protocols reported in sources
Displayed for reference only. Every row says where it came from, and a trial protocol and a community convention are not the same kind of information. None of this is fed into the calculator, and none of it is a recommendation.
| Goal | Dose | Frequency | Route | Units, 1 mg vial | Source | Start this protocol |
|---|---|---|---|---|---|---|
| Commonly described community protocol | 100 mcg – 300 mcg | Daily for a course of 10 to 30 days | SubcutaneousNo trial supports any of this. These figures circulate in community sources and assume the vial contains correctly folded, active protein. That is the assumption least likely to hold. | 10–30 u | Community practice | Start this |
Start this copies a row into a protocol of your own, which you can then edit. Where a source gave a dose range or an ambiguous frequency, those fields arrive empty — we will not pick a number on your behalf.
CheckRows marked community practice describe what people commonly do, drawn from public discussion. They are not derived from any trial and are not evidence that a dose is safe or effective.
Calculator
Work out what to draw
Pre-filled with a 1 mg vial as a worked example. These are not recommended values — change them to match the vial in front of you.
Draw to 40 units on a 1 mL U-100 syringe. That is 0.4 mL, containing 200 mcg of Follistatin-344.
40 units sits exactly on a printed line.
Bioalmanac performs arithmetic on values you enter. It does not recommend doses, schedules or compounds, and nothing here is medical advice. Confirm every calculation against your vial and syringe before drawing, and speak with a licensed healthcare provider.
Open this calculation in the full calculator
Units, concentration, bacteriostatic water — the glossary defines the vocabulary, and a unit is not a fixed volume.
Safety
Reported effects
- Nosebleeds and dilated skin blood vesselsClinical trial
Caused a related trial to be halted
Seen with ACE-031, a different myostatin inhibitor, in a phase 2 trial that was stopped early. Attributed to off-target activity in the same TGF-beta family that follistatin also binds.
- Effects on reproductive hormonesPublished review
Mechanistically expected, not measured in humans
Activin and follistatin regulate FSH release. Blocking activin systemically has predictable consequences for the reproductive axis that nobody has quantified for this compound.
- Immune response to a foreign or misfolded proteinPublished review
Unknown
Injecting an incorrectly folded 37 kDa protein risks an antibody response, potentially against your own follistatin. That would be worse than no effect at all.
- Everything elseCommunity practice
Unknown
No human has been studied on injected follistatin-344 under any protocol.
When to stop
- Nosebleeds, or new visible small blood vessels in the skin. These are the specific effects that halted the ACE-031 trials.
- Unusual bruising or bleeding that does not stop normally.
- Any allergic response: rash, hives, facial swelling or difficulty breathing. Seek urgent care.
- Changes in libido, menstrual cycle or testicular size, which would suggest reproductive axis effects.
- Any new lump or unexplained persistent pain.
Interactions and situations that need care
- Active or previous cancerAvoid
The TGF-beta family that follistatin antagonises includes signals that restrain cell proliferation. Blocking growth restraint broadly, in someone with malignancy, has an obvious mechanism for harm and no evidence to weigh against it.
- Any bleeding disorder, or anticoagulant therapyAvoid
The related myostatin inhibitor ACE-031 caused nosebleeds and vascular changes serious enough to stop its trials. Adding that to an existing bleeding tendency compounds a documented risk.
- Competing in a tested sportAvoid
Myostatin inhibitors are named as a class in WADA's S4.5 category and prohibited at all times, in and out of competition.
- Pregnancy and breastfeedingAvoid
Activin signalling is essential in development. Blocking it during pregnancy is a foreseeable and serious risk with no data at all.
- Assuming the vial contains active proteinUse caution
Producing correctly folded, glycosylated follistatin requires mammalian cell expression and costs far more than these vials sell for. Nothing you can observe establishes that a given vial contains functional protein, and no certificate of analysis a buyer can obtain tests for correct folding.
SportProhibited by the World Anti-Doping Agency under S4.5: Metabolic Modulators, myostatin inhibitors, at all times, in and out of competition. Myostatin-inhibiting agents are named as a class, whatever molecule delivers the effect.
What to expect
HonestlyThere is no human efficacy data for this compound, so there is no evidence-based timeline to give. Any site publishing a week-by-week schedule of expected effects has invented it.
- No human trial of injected follistatin-344 exists. Not a small one, not a poor one. None.
- The nearest pharmaceutical programme on this pathway was stopped for safety, after participants developed nosebleeds and vascular changes.
- It is a 344-residue glycoprotein, not a peptide. Whether an inexpensive vial contains correctly folded, glycosylated, active protein is genuinely doubtful, and you cannot tell by looking.
- The animal results are real and dramatic. They have not translated to a human treatment in twenty years of trying, which is information, not an oversight.
- Local injection to grow a specific muscle has no human evidence behind it and is inconsistent with how a secreted protein behaves.
Storage and handling
- Freeze-dried powder
- Refrigerated at 2–8 °C, protected from light.
- After mixing
- Refrigerated at 2–8 °C, and used quickly. A large glycoprotein is far less stable in solution than a short peptide, and it will not look any different once it has lost activity.
- Long-term, frozen
- Unopened powder at −20 °C or colder. Avoid freeze-thaw cycles entirely. Each one degrades a protein of this size.
With other peptides
- IGF-1 LR3caution
Both drive muscle growth through unregulated pathways. One removes a brake; the other supplies an accelerator. Neither has human safety data, the proliferative concerns compound, and no study has looked at the combination.
Checking your vial
Research chemicals carry no manufacturing standard, so what the vial looks like is often the only quality signal available before you use it. More on assessing quality and COAs.
White cake, clear solution after gentle swirling
Never shake a protein this size. Shaking denatures it, and denatured protein looks the same in the vial.
Cloudy solution or visible aggregate
Protein aggregation. It is not active, and injecting aggregated protein raises immune reaction risk.
Appearance tells you very little here
A correctly presented cake and a clear solution establish nothing about folding or glycosylation, which are what determine whether this protein works. Unlike short peptides, you cannot assess this one by looking at it.
Questions
- Is what I would be buying actually follistatin?
- That is the right first question, and there is no way for a buyer to answer it. Correctly folded, glycosylated follistatin requires mammalian cell expression at a cost far above typical vial prices. A certificate of analysis showing purity says nothing about folding. That is what determines whether the protein works at all.
- What happened with ACE-031?
- A different myostatin inhibitor that reached phase 2. The trials were stopped early after participants developed nosebleeds and dilated blood vessels in the skin. Those are off-target effects in the wider TGF-beta family that follistatin also acts on.
- Does injecting it into a muscle grow that muscle?
- No human data supports it. Follistatin is a secreted protein that enters circulation, so the premise of confining it to one site does not match how the molecule behaves.
References
Follistatin and myostatin inhibition: muscle growth and the breadth of TGF-beta signalling
Muscle biology review literature, 2018 · Review of animal and in vitro studies
Mice, non-human primates and in vitro
Documents substantial muscle growth from follistatin overexpression in animals, and notes that follistatin antagonises activin A and other TGF-beta family members with roles in reproduction, inflammation and vascular regulation.
Follistatin gene therapy in Becker muscular dystrophy: a phase 1/2a study
Molecular Therapy, 2015 · Open-label phase 1/2a gene therapy trial
Adults with Becker muscular dystrophy · n = 6 · Up to 2 years of follow-up
Reported improved six-minute walk distance in some participants after intramuscular AAV-delivered follistatin. A very small, unblinded gene therapy study. Not evidence about an injected protein.
ACE-031 in Duchenne muscular dystrophy: phase 2 trial discontinued for safety
Neuromuscular disorders literature, 2015 · Randomised, double-blind, placebo-controlled phase 2 trial
Boys with Duchenne muscular dystrophy
Discontinued early after participants developed epistaxis and telangiectasia, attributed to off-target activity within the TGF-beta family. The most instructive human safety data on pharmacological myostatin inhibition.
Commonly reported community protocols
Bioalmanac editorial summary of public community sources, 2026 · Not a study
Records dose and course patterns described in public discussion. No trial supports them, and they assume the product is biologically active.
Related compounds
IGF-1 LR3
A modified insulin-like growth factor engineered to last far longer in the body than the natural hormone. It can cause hypoglycaemia, which makes it the most acutely dangerous compound on this site.
Ipamorelin
A selective growth hormone secretagogue that prompts a short pulse of GH release. Widely used, and supported almost entirely by early pharmacology rather than outcome trials.
CJC-1295
A GHRH analogue that raises growth hormone by amplifying the body's own release signal. Sold in two forms whose durations differ by two orders of magnitude.
Tesamorelin
A GHRH analogue approved by the FDA for reducing excess visceral fat in HIV-associated lipodystrophy. The only compound in this category with completed phase 3 trials.
Next
What to do with Follistatin-344
- Keep a record of itTurn a dose and a schedule into a protocol, then log what you actually take. Follistatin-344 is filled in for you.
- See what it costsPer-milligram prices read from vendor sites and confirmed by a person, so vial sizes compare.
- Check a combinationWhat our profiles record about Follistatin-344 alongside each other compound — including the pairs where nothing is recorded.
Keep this page honest
If something here is wrong, out of date, or missing a source, tell us and we will fix it and say that we did.
This page is educational. It describes what published research reports, not what you should do. Peptides discussed here are largely not approved for human use, and nothing on Bioalmanac is medical advice. No clinician reviews these pages.
Page last updated 16 Aug 2026