--- title: "Follistatin-344: Benefits, Side Effects & Myostatin" description: "Follistatin-344 binds myostatin, the brake on muscle growth. What mouse and gene therapy trials show, why black-market vials differ, and side effects." canonical: "https://www.vitalsvault.com/peptides/follistatin-344" last-updated: 2026-08-22 --- # Follistatin-344: Benefits, Side Effects & Myostatin > Follistatin-344 binds myostatin, the brake on muscle growth. What mouse and gene therapy trials show, why black-market vials differ, and side effects. ![A Filipino woman, 63, tall, silver pixie cut, gold-rimmed glasses, a small mole on her cheek, sits on a bench in a bright home studio with…](https://www.vitalsvault.com/_next/image?url=%2Fpublic-v3%2Fshoot%2Fpeptides%2Fpep-follistatin.webp&w=3840&q=75&dpl=shadow-production-f0162cb4d465-40992538108-1) Peptide Guide · Growth hormone and muscle # Follistatin-344 FS344, FST-344, follistatin 344 Mice without myostatin carry muscles two to three times the normal weight. Follistatin is the protein your body uses to hold myostatin back, which is why it fascinates anyone who wants more muscle. [Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist)[Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) Free to join · One email when peptide care opens · Most lab results in 3–5 business days Studied forMuscle mass and strength by blocking myostatin EvidenceEarly research Taken asInjection, from unregulated sources Studied forMuscle mass and strength by blocking myostatin EvidenceEarly research Taken asInjection, from unregulated sources ## Follistatin-344, in short Follistatin-344 is a form of follistatin, a protein the body makes to bind myostatin and activin, two signals that limit muscle growth. Mice engineered to make extra follistatin grew dramatically more muscle. In people, FS344 has been tested as gene therapy in small trials for muscle disease, and no published study has tested the injected protein. Medically reviewed by [Robert Lufkin, MD (opens in a new tab)](https://www.robertlufkinmd.com/) Chief Medical Officer, Vitals Vault · Updated October 29, 2026 · 13 sources ## At a glance Early research TypeProtein (a splice form of follistatin), around 315 amino acids once secreted[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009) TargetMyostatin and activin, which limit muscle growth[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[3](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2010) Studied forMuscle mass and strength[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015) Human dataSmall gene therapy trials in muscle disease. None published for injected FS344 protein[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017) Taken asInjection, from unregulated sources FDA statusNot approved. Not listed on FDA’s April 2026 compounding safety page[12](https://www.vitalsvault.com/peptides/follistatin-344#source-fda-bulks) SportProhibited by WADA (S4, myostatin-inhibiting proteins)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019)[13](https://www.vitalsvault.com/peptides/follistatin-344#source-wada) ## Before you consider Follistatin-344 - Safety A gene therapy trial in six people reported no adverse effects. No safety data exist for injected protein, and high follistatin weakened bone in mice.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020) [Side effects and safety](https://www.vitalsvault.com/peptides/follistatin-344#safety) - Legal status Not FDA approved, and it does not appear on FDA’s compounding safety page. No approved follistatin products exist.[12](https://www.vitalsvault.com/peptides/follistatin-344#source-fda-bulks)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) [FDA status](https://www.vitalsvault.com/peptides/follistatin-344#fda-status) - How it’s taken In trials it was gene therapy injected into thigh muscle. Injectable protein is sold through unregulated channels, where purity cannot be assumed.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) [Forms and dosage](https://www.vitalsvault.com/peptides/follistatin-344#how-taken) ## How does Follistatin-344 work? Follistatin removes a brake on muscle by soaking up the signals that apply it. - ### Soaks up myostatin Myostatin tells muscle to stop growing. In the lab, follistatin kept it from reaching its target.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001) - ### Soaks up activin too Mouse genetics suggest follistatin also holds back activin A, another signal that limits muscle size.[3](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2010) - ### Muscle grows in mice Mice made to produce extra follistatin in muscle gained dramatic muscle mass, like mice with no myostatin.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001) ## Follistatin-344 benefits: what it is studied for The mouse results are striking. In people, the only studies are small gene therapy trials, not injected protein, so this is early research. 1. Animal study01 ### Muscle mass in mice Transgenic mice expressing follistatin in muscle had dramatic increases in muscle mass.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001) 2. Human study02 ### Walking distance in Becker muscular dystrophy After follistatin gene therapy into thigh muscle, 4 of 6 patients walked farther in 6 minutes, with no adverse effects reported. There was no control group.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015) 3. Human study03 ### Inclusion body myositis In six people with sporadic inclusion body myositis, gene therapy was followed by a better 6-minute walk than an untreated comparison group. A published commentary challenged that result.[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017)[6](https://www.vitalsvault.com/peptides/follistatin-344#source-greenberg-2017) ## What the research shows Early research 1. 1 · Cells in a lab Studied Follistatin blocked myostatin from binding its target in lab experiments.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001) Shows a mechanism 2. 2 · Animals Studied Mice made to produce extra follistatin in muscle gained dramatic muscle mass, but had weaker bones.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020) Shows an effect in a body 3. 3 · People Studied Two small gene therapy trials, six people each, showed longer walks in muscle disease. No study has tested injected protein.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017) Shows it works in people The mouse work is strong. The human trials delivered the follistatin gene into muscle with a virus. They do not show that injecting follistatin protein works or is safe.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) A doping-control laboratory tested 17 black-market products labeled follistatin. Only nine contained it, and some of the others held different growth-promoting peptides.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) The full guide to Follistatin-344 9 min read · Medically reviewed by Robert Lufkin, MD ## The brake on muscle, and the protein that releases it In 1997, a lab in Baltimore deleted a single gene in mice and got animals that looked as if they had been lifting weights since birth. Individual muscles weighed two to three times more than normal, built from both more and larger muscle fibers. The gene coded for a growth factor the team named GDF-8. Today it is better known as myostatin. Myostatin turned out to be the body’s brake on muscle growth, a member of the TGF-beta family of signals that tells muscle when to stop. In 2004, doctors in Berlin described a child with a myostatin mutation and gross muscle hypertrophy, a human echo of the Baltimore mice. The brake was real in people too. If removing the brake builds muscle, the next question was how to release it in someone who still has the gene. The body already makes a protein that does something close to that. It is called follistatin, and Follistatin-344 is the research name for one of its forms. Its story runs from the ovary to gene therapy trials to a black market that sells something quite different from what the trials used.[9](https://www.vitalsvault.com/peptides/follistatin-344#source-mcpherron-1997)[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[10](https://www.vitalsvault.com/peptides/follistatin-344#source-schuelke-2004) ## What follistatin is, and why it started in the ovary Follistatin was first isolated from the ovary, where it suppresses follicle-stimulating hormone, FSH, the pituitary signal that drives egg development in women and sperm production in men. Its muscle role came later, when researchers found that it binds activin and myostatin, two members of the same signaling family. That history explains both its promise and its risk. Follistatin is a binding protein that traps several related signals at once. Trap myostatin and muscle grows. Trap activin as well and reproductive hormones can shift, which is why its developers worried from the start about effects on the hypothalamic-pituitary-gonadal axis, the hormone chain that runs fertility. It is also large. The form released from muscle in the gene therapy work is 315 amino acids long, while BPC-157, for comparison, has 15. Calling follistatin a peptide stretches the word; it is a full protein, with everything that implies for how it is made, stored and handled by the immune system.[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009)[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[3](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2010) ## How follistatin works: trapping myostatin and activin Myostatin acts by docking onto activin type II receptors on muscle cells, mainly one called ActRIIB. In 2001 the Baltimore group showed that follistatin blocks that docking in the lab. They then built mice whose muscles overproduced follistatin. Independent lines of these mice showed dramatic increases in muscle mass, comparable to mice that lack myostatin entirely. A 2010 study added a twist. Mice with only one working follistatin gene had smaller muscles that produced less force, which fits a protein that restrains myostatin. But the effect partly persisted in mice that also lacked myostatin. Follistatin was holding back something else as well, and the genetic evidence pointed to activin A. So follistatin works as a broad release of the brakes, mopping up a family of related signals, each with jobs beyond muscle. That breadth is why it builds muscle so dramatically in mice, and also why it is hard to use safely. A drug designer would usually want the opposite, a molecule that hits one target and leaves the rest alone. Follistatin evolved to regulate a whole neighborhood of signals, and it does that wherever it travels.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[3](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2010) ## Follistatin benefits in animals The mouse results are among the most striking in muscle biology. Transgenic mice making extra follistatin in muscle carried far more muscle than normal mice. A team at Nationwide Children’s Hospital in Columbus, Ohio, then used gene therapy to deliver the FS344 form to muscle and reported larger, stronger muscles in species ranging from mice to monkeys. In those studies the team reported no organ damage and no change in reproductive capability, which addressed the FSH worry for that delivery method. The key design choice was the FS344 gene. Its product circulates in the blood instead of sticking to binding sites on cell surfaces, which the team argued limited off-target effects. Gene therapy also kept production local and continuous, so the muscle itself became the source. That design choice is easy to overlook, and it matters later, because it is the part a vial cannot copy. The bone story is less reassuring. In a 2020 study, mice overproducing follistatin had more muscle but weaker bones and fractures, while mice lacking myostatin had more muscle and stronger bones. The difference traced to GDF11, a close relative of myostatin that helps build bone and that follistatin also blocks.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009)[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020) ## The human trials: gene therapy in muscle disease In the trials cited here, follistatin reached people as gene therapy, not as an injected protein. Engineered drugs built partly from follistatin are a separate line of work. In a phase 1/2a trial for Becker muscular dystrophy, an inherited muscle-wasting disease, six patients received a virus carrying the FS344 gene, injected directly into both thigh muscles. The main measure was the 6-minute walk test, how far someone can walk in six minutes. Four of the six walked farther, by 58, 125, 108 and 29 meters. Two did not improve. Muscle biopsies showed less scarring and a more normal spread of fiber sizes, with larger fibers especially at the higher dose, and no adverse effects were reported. For a disease with no treatment at the time, the result was encouraging, and very small. A 2017 trial in sporadic inclusion body myositis, a muscle disease that mostly begins after age 50, used the same approach in six patients along with an exercise program. Treated patients gained a median of 56 meters a year on the walk test, while an untreated comparison group declined by about 26 meters a year. Four of the six gained between 58 and 153 meters. Not everyone accepted that reading. A researcher in Boston published a commentary in the same journal under the title Unfounded claims of improved functional outcomes attributed to follistatin gene therapy in inclusion body myositis. With six patients, an exercise program alongside and an outside comparison group, the dispute is easy to understand. Neither trial tested follistatin protein given by injection.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017)[6](https://www.vitalsvault.com/peptides/follistatin-344#source-greenberg-2017) ## Why the 344 in Follistatin-344 names a gene The number in Follistatin-344 has a specific meaning. FS344 is the 344-amino-acid precursor encoded by one alternatively spliced follistatin transcript, in effect one edition of the recipe. When muscle reads that recipe after gene therapy, it trims off a short signal sequence and releases a 315-amino-acid protein into the blood. Researchers chose FS344 precisely because that circulating form avoids the cell-surface binding of other forms. Now look at what is sold under that name. In 2019, a doping-control laboratory tested 17 black-market products labeled follistatin, most of them FS344. Only nine contained follistatin at all. Several of the others held different growth-promoting peptides, including MGF and GHRP-2. The nine genuine products held a surprise. Every one contained FS344 with a His-tag, a short run of histidines that scientists attach to proteins so they can purify them in the lab, and a high share of the protein had clumped into larger complexes called oligomers. The vials looked like laboratory reagent protein built from a gene therapy sequence, then sold for injection. This is where a hypothesis is fair to state. Gene therapy turns muscle into a local factory that keeps producing follistatin. An injected protein, tagged, partly clumped and without published human data, is a different exposure, and nothing shows it reproduces what the trials saw. Clumped and tagged proteins may also provoke the immune system, a known concern for protein drugs that has never been measured for these products.[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019)[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015) Know your baseline before any peptide 120+ lab tests at Quest Diagnostics, every result reviewed by a licensed clinician. Most results in 3–5 business days. A baseline today gives your clinician something to compare against if you start Follistatin-344 later. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans)[Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist) Full refund before your blood draw · No membership ## The cost of releasing the brake: lessons from ACE-031 Follistatin is not the only way to block myostatin, and a related drug shows what can go wrong. ACE-031 was a fusion protein built from the ActRIIB receptor that soaked up myostatin and its relatives. In a randomized, placebo-controlled trial, it was injected under the skin of boys with Duchenne muscular dystrophy, the most common inherited muscle-wasting disease of childhood. Safety was the primary goal of the study, and the dose was raised step by step. The trial stopped early, after the second dosing level, because of nosebleeds and telangiectasias, small dilated blood vessels in the skin. There were trends toward more lean mass, less fat, better bone density and a better-preserved walking distance, though the walking result was not statistically significant. The side effects that ended the study were not muscle-related. The lesson carries over to follistatin. Myostatin’s relatives do other jobs. GDF11 helps build bone, and activin works in the reproductive axis. A drug that traps the family reaches those systems too, and in the case of ACE-031 the trouble appeared in blood vessels, far from the muscle it was meant to help.[11](https://www.vitalsvault.com/peptides/follistatin-344#source-campbell-2017)[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020)[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009) ## Follistatin-344 side effects and safety No human safety data have been published for injected FS344 protein. The Becker gene therapy trial reported no adverse effects, and the inclusion body myositis report described no adverse events tied to treatment, but both used a different delivery method, in people with muscle disease, under close monitoring. Six patients per trial is also far too few to detect uncommon side effects, so even for gene therapy the safety record is only a starting point. From the biology, three risks stand out. Follistatin suppresses FSH, so it could disturb fertility and the reproductive hormone axis. It blocks GDF11, and in mice that weakened bone. And protein products of uncertain make-up carry immune and contamination risks of their own. The supply makes those risks harder to judge. Nearly half the black-market products in the 2019 study did not contain follistatin, and some held other growth-promoting peptides with side effects of their own. Tested athletes should also know that the His-tag lets anti-doping labs tell black-market follistatin apart from the body’s own. Talk to a clinician first if you are pregnant, breastfeeding or trying to conceive, have a history of cancer, have low bone density, or compete in tested sport.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009)[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) ## Hormone labs that matter around follistatin Because follistatin started life as an FSH suppressor, the reproductive hormone axis is the first thing worth checking. FSH and LH are the pituitary signals that drive the testes and ovaries. Follistatin’s effect on activin raises a fair question about FSH, though no study has set out a hormone pattern to watch for with injected FS344. Total testosterone and estradiol add the gonad side of that picture, though estradiol in men also reflects conversion from testosterone in other tissues. Read together by a clinician, the four markers give context on the hormone axis behind muscle, libido and fertility. Vitals Vault does not offer Follistatin-344. A clinician may order these when symptoms, history or an approach that touches the hormone system make them relevant, and they are general context, not a test that makes any compound safe. If something in the axis is already off, such as low testosterone or a high estradiol, that is usually a better place to start than a muscle-growth compound, and it can be retested to see whether a change is working.[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009) ## Is Follistatin-344 legal? Follistatin-344 is not an FDA-approved drug, and it does not appear on FDA’s compounding safety page, current as of April 22, 2026. A 2019 doping-control study noted that no approved pharmaceutical formulation of follistatin was available. The World Anti-Doping Agency lists follistatin under S4 as a myostatin-inhibiting protein, prohibited at all times, and anti-doping scientists have developed a method to detect the black-market form in urine and serum. Because the black-market protein carries a His-tag, a positive result cannot be explained away as the body’s own follistatin.[12](https://www.vitalsvault.com/peptides/follistatin-344#source-fda-bulks)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019)[13](https://www.vitalsvault.com/peptides/follistatin-344#source-wada) ## What this means for you Follistatin sits on top of one of the cleanest stories in muscle biology. Remove the myostatin brake and muscle grows, in mice and in a child born with the mutation. Follistatin is the body’s own way to ease that brake, and after gene therapy a few people with muscle disease walked farther, in trials too small to prove cause. In one analysis of 17 black-market vials sold as follistatin, nine held a tagged laboratory protein and eight held no follistatin at all. None has human data, and follistatin’s biology raises reproductive concerns and weakened bone in mice. If muscle is your goal, the next question worth asking is which brake is actually limiting you, and whether training, protein, sleep and hormones have been measured and addressed first.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[10](https://www.vitalsvault.com/peptides/follistatin-344#source-schuelke-2004)[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) Know your baseline before any peptide 120+ lab tests at Quest Diagnostics, every result reviewed by a licensed clinician. Most results in 3–5 business days. A baseline today gives your clinician something to compare against if you start Follistatin-344 later. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans)[Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist) Full refund before your blood draw · No membership ## What to expect with Follistatin-344 There is no human timeline for injected follistatin, because no published study has tested the FS344 protein that way. In the gene therapy trials, walking distance was tracked over months, and the inclusion body myositis results were expressed as change over a year. If muscle is the goal, a more reliable timeline comes from training. Strength and muscle size respond over weeks to months of progressive resistance work and enough protein, and a hormone panel at the start gives a clinician a baseline to compare against.[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017)[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015) ## Key Follistatin-344 studies - McPherron et al., 1997[9](https://www.vitalsvault.com/peptides/follistatin-344#source-mcpherron-1997) Animal study · Mice lacking the GDF-8 (myostatin) gene Individual muscles weighed two to three times normal Limits: Genetic deletion, not a treatment - Lee and McPherron, 2001[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001) Lab and animal study · Transgenic mice making extra follistatin in muscle Follistatin blocked myostatin binding; mice gained dramatic muscle mass Limits: Lifelong genetic overexpression in mice - Lee et al., 2010[3](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2010) Genetic animal study · Mice with one working follistatin gene Smaller muscles; follistatin also restrains activin A Limits: Mice - Mendell et al., 2015[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015) Phase 1/2a gene therapy trial · 6 adults with Becker muscular dystrophy 4 of 6 walked 29 to 125 meters farther after treatment; no adverse effects reported Limits: Tiny, uncontrolled; gene therapy, not injected protein - Mendell et al., 2017[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017)[6](https://www.vitalsvault.com/peptides/follistatin-344#source-greenberg-2017) Gene therapy trial with exercise · 6 adults with inclusion body myositis Walk distance rose about 56 meters a year versus a decline in comparison patients Limits: Outside comparison group; findings disputed in a published commentary - Campbell et al., 2017[11](https://www.vitalsvault.com/peptides/follistatin-344#source-campbell-2017) Randomized, placebo-controlled trial · Boys with Duchenne muscular dystrophy ACE-031, a myostatin-family blocker, stopped early for nosebleeds and skin vessel changes Limits: A related drug, not follistatin - Reichel et al., 2019[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) Laboratory analysis · 17 black-market follistatin products Only 9 contained follistatin, all His-tagged and partly clumped Limits: Product testing, no health outcomes - Suh et al., 2020[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020) Genetic animal study · Mice overproducing follistatin More muscle but weaker bones and fractures Limits: Mice Key studies on Follistatin-344 | Study | Design | Who | What it found | Limits | | --- | --- | --- | --- | --- | | McPherron et al., 1997[9](https://www.vitalsvault.com/peptides/follistatin-344#source-mcpherron-1997) | Animal study | Mice lacking the GDF-8 (myostatin) gene | Individual muscles weighed two to three times normal | Genetic deletion, not a treatment | | Lee and McPherron, 2001[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001) | Lab and animal study | Transgenic mice making extra follistatin in muscle | Follistatin blocked myostatin binding; mice gained dramatic muscle mass | Lifelong genetic overexpression in mice | | Lee et al., 2010[3](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2010) | Genetic animal study | Mice with one working follistatin gene | Smaller muscles; follistatin also restrains activin A | Mice | | Mendell et al., 2015[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015) | Phase 1/2a gene therapy trial | 6 adults with Becker muscular dystrophy | 4 of 6 walked 29 to 125 meters farther after treatment; no adverse effects reported | Tiny, uncontrolled; gene therapy, not injected protein | | Mendell et al., 2017[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017)[6](https://www.vitalsvault.com/peptides/follistatin-344#source-greenberg-2017) | Gene therapy trial with exercise | 6 adults with inclusion body myositis | Walk distance rose about 56 meters a year versus a decline in comparison patients | Outside comparison group; findings disputed in a published commentary | | Campbell et al., 2017[11](https://www.vitalsvault.com/peptides/follistatin-344#source-campbell-2017) | Randomized, placebo-controlled trial | Boys with Duchenne muscular dystrophy | ACE-031, a myostatin-family blocker, stopped early for nosebleeds and skin vessel changes | A related drug, not follistatin | | Reichel et al., 2019[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) | Laboratory analysis | 17 black-market follistatin products | Only 9 contained follistatin, all His-tagged and partly clumped | Product testing, no health outcomes | | Suh et al., 2020[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020) | Genetic animal study | Mice overproducing follistatin | More muscle but weaker bones and fractures | Mice | ## Follistatin-344 myths and evidence - ### Follistatin-344 is a peptide like BPC-157 It is a full protein. The circulating form made after FS344 gene therapy is 315 amino acids long, compared with 15 for BPC-157.[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009) - ### Injecting follistatin works like the gene therapy trials The human trials delivered the FS344 gene into thigh muscle, so muscle made the protein itself. No published study has tested injected FS344 protein in people.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017) - ### Blocking myostatin only affects muscle Follistatin also binds activin and GDF11. It suppresses FSH, and high follistatin weakened bone in mice. A related myostatin-family blocker, ACE-031, was stopped for nosebleeds and skin vessel changes.[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009)[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020)[11](https://www.vitalsvault.com/peptides/follistatin-344#source-campbell-2017) - ### A vial labeled follistatin contains follistatin In a 2019 analysis, only 9 of 17 black-market products did. Some others contained different growth-promoting peptides, and all the genuine ones were His-tagged lab-style protein with clumping.[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) Know your baseline first 120+ lab tests at Quest, every result reviewed by a licensed clinician. Most results in 3–5 business days. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) ## How is Follistatin-344 taken? In human trials follistatin was delivered by gene therapy, a virus carrying the gene injected into thigh muscle. Injectable protein is sold through unregulated channels, where identity and purity cannot be assumed.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) ## Follistatin-344 dosage There is no FDA-approved dose of Follistatin-344 and no typical human dose of the protein. The only studies in people were gene therapy trials that gave a one-time injection into the thigh muscles to make the body produce follistatin, and those doses do not apply to injected protein. Your clinician decides whether any use makes sense.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015)[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017) ## Typical Follistatin-344 dosage No dose of Follistatin-344 protein has been published from a study in people, an FDA label or a clinical practice report, so there is no typical human dose to show. The human trials were one-time gene therapy injections into the thigh muscles in people with muscle disease, which is a different treatment from injecting the protein. A clinician decides any use. These are reference doses from FDA labels, studies in people and clinical practice reports, shown for education. They are not a recommendation or a prescription. Your dose, form and schedule should be set by a licensed clinician who knows your history and lab results. Already have a prescribed dose? The [peptide dosage calculator](https://www.vitalsvault.com/peptides/tools/dosage-calculator) turns it into the units to draw on an insulin syringe. No dose has been published from studies in people yet, so there is no typical dose to show. A prescribing clinician decides whether Follistatin-344 fits and how it is given. ## Is Follistatin-344 right for you? A clinician makes the call. These are the questions they will ask first. ### It may suit - Adults who want to understand myostatin research before choosing a muscle-building approach - People who want a baseline of reproductive and metabolic labs reviewed by a clinician ### Talk to a clinician first if you are - Pregnant or breastfeeding, or trying to conceive, because follistatin acts on FSH and activin - A history of cancer, because growth-promoting pathways are involved - Competing in tested sport, where follistatin is prohibited - Bone density concerns, because high follistatin weakened bone in mice - Any reproductive hormone condition Vitals Vault peptide care starts with a blood panel and a licensed clinician, and ends with a retest. [Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist) ## Muscle is a hormone organ with built-in brakes Muscle size is not set by training alone. Signals such as myostatin and activin tell muscle to stop growing. Follistatin is part of the counter-signal. In mice with only one working follistatin gene, muscles were smaller. That same logic is why the approach carries risks. Follistatin does not bind only myostatin. It also binds activin and is known to suppress FSH. In mice, high follistatin built muscle but weakened bone. An injected protein from an unregulated supply is a different thing from a controlled gene therapy trial.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001)[3](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2010)[8](https://www.vitalsvault.com/peptides/follistatin-344#source-suh-2020)[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009) ### What else moves the same system 1. 01Lift heavyResistance training is the best-supported way to grow muscle and strengthens bone at the same time. 2. 02Eat enough proteinMuscle protein synthesis depends on a steady supply of amino acids across the day. 3. 03Sleep and recoverGrowth and repair signals run mostly at night. 4. 04Check the hormonesTestosterone, LH, FSH and estradiol show how the axis behind muscle is running. ## Labs to check with Follistatin-344 A blood test before you start and a retest after shows what actually changed for you. It is how Vitals Vault approaches every treatment. 1. TestA baseline panel at Quest Diagnostics. 2. DecideA licensed clinician reviews your history and results. 3. RetestThe same markers again, side by side. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) - [Total testosteroneGeneral context on the hormone axis behind muscle, read by a clinician alongside symptoms and history.](https://www.vitalsvault.com/biomarkers/testosterone-total) - [FSHFollistatin is known to suppress follicle-stimulating hormone, so FSH is relevant background for a clinician reviewing the reproductive axis.](https://www.vitalsvault.com/biomarkers/fsh) - [LHPairs with FSH and testosterone to show how the reproductive hormone axis is running.](https://www.vitalsvault.com/biomarkers/lh) - [EstradiolPart of a full sex-hormone picture alongside testosterone and FSH.](https://www.vitalsvault.com/biomarkers/estradiol) ## Is Follistatin-344 FDA approved? No. Follistatin-344 is not an FDA-approved drug and does not appear on FDA’s compounding safety page (current as of April 22, 2026). A 2019 doping-control study noted that no approved pharmaceutical formulations of follistatin exist.[12](https://www.vitalsvault.com/peptides/follistatin-344#source-fda-bulks)[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) ### Follistatin-344 timeline 1. 2001 Follistatin is shown to block myostatin binding, and follistatin-expressing mice show large increases in muscle mass.[1](https://www.vitalsvault.com/peptides/follistatin-344#source-lee-2001) 2. 2009 Researchers propose the FS344 form delivered by gene therapy to bypass off-target binding and move toward clinical trials.[2](https://www.vitalsvault.com/peptides/follistatin-344#source-rodino-klapac-2009) 3. 2015 A phase 1/2a gene therapy trial of FS344 in Becker muscular dystrophy reports improved walking distance in four of six patients.[4](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2015) 4. 2017 A follistatin gene therapy trial in inclusion body myositis reports improved walking distance, and a published commentary disputes the claims.[5](https://www.vitalsvault.com/peptides/follistatin-344#source-mendell-2017)[6](https://www.vitalsvault.com/peptides/follistatin-344#source-greenberg-2017) 5. 2019 A doping-control study finds that only nine of 17 black-market follistatin products contained follistatin.[7](https://www.vitalsvault.com/peptides/follistatin-344#source-reichel-2019) ![A Pacific Islander woman, 54, tall, long grey-black hair, freckled arms writes on a cottage porch swing](https://www.vitalsvault.com/_next/image?url=%2Fpublic-v3%2Fshoot%2Fpeptides%2Ffaq-follistatin344.webp&w=3840&q=75&dpl=shadow-production-f0162cb4d465-40992538108-1) ## Follistatin-344 questions What is Follistatin-344 used for? Follistatin-344 is studied for muscle mass and strength because it blocks myostatin. It is not FDA-approved. Human trials have used gene therapy in people with muscle disease, not injected protein. What are the benefits of Follistatin-344? In mice it produced dramatic increases in muscle mass. In small gene therapy trials, some people with muscle disease walked farther, though trials this small cannot show the therapy caused it. These results do not apply to injected protein sold online. How does Follistatin-344 work? It binds myostatin and activin, two signals that limit muscle growth, so muscle receives less of the brake signal. What are the side effects of Follistatin-344? No human safety data have been published for injected FS344 protein. Follistatin affects FSH and activin, and high follistatin weakened bone in mice. In one analysis, 8 of 17 black-market products contained no follistatin. What is the Follistatin-344 dosage? There is no FDA-approved dose and no typical human dose of the protein. The only human trials used one-time gene therapy injections into muscle, and those doses do not translate to protein injections. Your clinician decides whether any use makes sense. Follistatin-344 vs myostatin, how are they related? Myostatin limits muscle growth. Follistatin binds myostatin and blocks it. Mice with extra follistatin in muscle grew muscle like mice lacking myostatin. Is Follistatin-344 a peptide? Not in the usual sense. The secreted form is around 315 amino acids, which makes it a protein. Sellers list it with peptides. Is Follistatin-344 FDA approved? No. It is not an FDA-approved drug and does not appear on FDA’s April 2026 compounding safety page. Is Follistatin-344 banned in sport? Yes. The World Anti-Doping Agency prohibits follistatin as a myostatin-inhibiting protein. Athletes in tested sport should not use it. Can I get Follistatin-344 through Vitals Vault? Not at this time. Vitals Vault is opening clinician-led peptide care that starts with a blood test, and Follistatin-344 is not part of it. Join the peptides waitlist to hear what is offered. ## Peptides, prescribed and measured Vitals Vault is opening peptide care that starts with your blood work, is prescribed by licensed US clinicians and ends with a retest. Join the waitlist to hear first. - Prescription only - Licensed US clinicians - Quest Diagnostics labs [Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist)[Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) ## Keep reading [Full Peptide Guide](https://www.vitalsvault.com/peptides) - IGF-1 LR3A lab-modified IGF-1 that resists its binding proteins, studied in cells and animals and never approved for people. - Mechano growth factor (MGF)A splice variant of the IGF-1 gene that muscle makes after mechanical load, studied for muscle stem cell activation. - IpamorelinA five-amino-acid growth hormone secretagogue that mimics ghrelin, studied for its selective release of growth hormone. - FDA peptide update 2026What FDA’s October 2026 decision on six peptides means for you. - CJC-1295A long-acting growth hormone releasing hormone analog, studied for raising growth hormone and IGF-1. ## Sources 1. 1. [Lee SJ, et al. Regulation of myostatin activity and muscle growth. Proc Natl Acad Sci U S A. 2001 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/11459935/) 2. 2. [Rodino-Klapac LR, et al. Inhibition of myostatin with emphasis on follistatin as a therapy for muscle disease. Muscle Nerve. 2009 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/19208403/) 3. 3. [Lee SJ, et al. Regulation of muscle mass by follistatin and activins. Mol Endocrinol. 2010 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/20810712/) 4. 4. [Mendell JR, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy. Mol Ther. 2015 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/25322757/) 5. 5. [Mendell JR, et al. Follistatin gene therapy for sporadic inclusion body myositis improves functional outcomes. Mol Ther. 2017 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/28279643/) 6. 6. [Greenberg SA. Unfounded claims of improved functional outcomes attributed to follistatin gene therapy in inclusion body myositis. Mol Ther. 2017 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/28927986/) 7. 7. [Reichel C, et al. Detection of black market follistatin 344. Drug Test Anal. 2019 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/31758732/) 8. 8. [Suh J, et al. GDF11 promotes osteogenesis as opposed to MSTN, and follistatin, a MSTN/GDF11 inhibitor, increases muscle mass but weakens bone. Proc Natl Acad Sci U S A. 2020 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/32071240/) 9. 9. [McPherron AC, et al. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member. Nature. 1997 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/9139826/) 10. 10. [Schuelke M, et al. Myostatin mutation associated with gross muscle hypertrophy in a child. N Engl J Med. 2004 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/15215484/) 11. 11. [Campbell C, et al. Myostatin inhibitor ACE-031 in ambulatory boys with Duchenne muscular dystrophy: results of a randomized, placebo-controlled clinical trial. Muscle Nerve. 2017 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/27462804/) 12. 12. [FDA. Certain bulk drug substances for use in compounding that may present significant safety risks (current as of April 22, 2026) (opens in a new tab)](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks) 13. 13. [World Anti-Doping Agency. Prohibited List (opens in a new tab)](https://www.wada-ama.org/en/prohibited-list) Written by the Vitals Vault editorial team, medically reviewed by Robert Lufkin, MD, and updated October 29, 2026. This is general education, not medical advice. None of these peptides is FDA-approved to diagnose, treat, cure or prevent any disease, and compounded medicines are not FDA-reviewed for safety, effectiveness or quality. 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