100 to 200 mcg a day under the skin, in cycles of 10 to 30 days, community convention not a tested dose
What was studied
No study I found gave the protein to a person on its own, by any route
The gap
No published human dose to compare against
How long it lasts
This entry gives no figure. I found no pharmacokinetic study, meaning a measurement of how much reaches the blood and how fast, of follistatin protein under the skin in any species. The nearest evidence is sheep, where four compounds were injected under the skin, three animals each, and the conclusion was that molecules above about 16,000 daltons are absorbed mainly by lymph, which is slow and partial. Follistatin is about twice that mass.
What it actually is
Follistatin-344 is the name of a stretch of DNA, not the name of a protein. A cell reads that stretch and makes a protein 315 units long, because the first 29 units are an address label that is snipped off as the protein leaves the cell, so no finished follistatin anywhere in human biology is 344 units long. It is also not a peptide in the usual sense. A peptide is a short chain, and this is a folded protein of roughly 35 to 38 kilodaltons, with UniProt giving the 344 unit precursor 38,007 daltons, roughly a hundred times the weight of a small peptide like epithalon, held in shape by 18 chemical staples and carrying sugar attachments the bacterial version does not have. What is sold in vials is a bacterial version with a manufacturing handle still bolted to it.
What it is supposed to do
Myostatin is a protein that tells muscle to stop growing, and follistatin is one of the proteins that mops it up before it reaches its receptor, the docking point it has to land on to do anything. That is the whole appeal. The catch is the delivery: every positive result I found under this name was produced by putting the gene into muscle, either on a virus or as a plasmid, so the muscle fibre makes the protein itself and keeps making it for months, which is not what an injection under the skin does. Follistatin was first isolated from the ovary and suppresses follicle stimulating hormone, the pituitary signal that drives egg and sperm production, and the group that took it into people named that as the reason for their design, choosing the version of the gene whose product circulates in blood rather than the short one that sticks to cell surfaces. On whether the bacterially made protein people actually inject binds myostatin at all, I found nothing published.
What people take it for
It is sold and talked about for muscle growth, and the numbers that travel with it belong to other things. The quadrupled muscle figure in marketing comes from a mouse bred both to carry a follistatin transgene and to have no myostatin. The largest human muscle figure I found, thigh volume up by an average of 14.5 percent at its maximum in 58 healthy postmenopausal women, belongs to ACE-083, a truncated follistatin coupled to an antibody Fc domain and engineered to stay in the muscle it is put into, and strength did not change. A phase 2 sarcopenia trial with lean mass figures circulates on vendor pages, and I could not find it on PubMed or among the 79 follistatin studies on the government registry. It also appears in hair loss marketing, where the human study I found behind the claim gave a cell derived mixture containing follistatin alongside two other growth factors rather than follistatin on its own.
The dose question
What circulates
100 to 200 mcg a day under the skin, in cycles of 10 to 30 days, community convention not a tested dose
What was studied
No study I found gave the protein to a person on its own, by any route
93 PubMed clinical trial records and 79 registry studies searched, and every human study I found that gave follistatin gave a gene
No studied dose to compare
There is nothing to compare against, because I found no published study giving follistatin protein to a person on its own by any route. Every human result I found under this name came from delivering the gene, carried in by a virus or given as a plasmid, which is a loop of bare DNA, and a gene keeps expressing inside a muscle fibre for months in a way an injection does not. The doses in the gene therapy record are counts of gene carrying virus particles per kilogram of body weight, and those do not convert into micrograms of protein. The two masses in the record run the other way: ACE-083, an engineered follistatin fusion, used 50 to 200 mg into one muscle, 250 to 2,000 times the daily microgram convention, and the dosage page carrying the convention concedes that no published human dose-response studies exist.
Reported because it is what people use. Nothing here recommends any amount.
How long it lasts
This entry gives no figure. I found no pharmacokinetic study, meaning a measurement of how much reaches the blood and how fast, of follistatin protein under the skin in any species. The nearest evidence is sheep, where four compounds were injected under the skin, three animals each, and the conclusion was that molecules above about 16,000 daltons are absorbed mainly by lymph, which is slow and partial. Follistatin is about twice that mass.
Route studied
As a gene. Into muscle, carried by a virus, in the published muscular dystrophy and myositis trials, and as a plasmid, a loop of bare DNA, in a commercial study of 43 healthy subjects in Honduras that has posted no results. ACE-083, a different engineered molecule, went into one named muscle at 50 to 200 mg.
Route used
Injected under the skin, from vials sold under the gene's name.
How to check you have the right molecule
One line on the paperwork does most of the work: whether the certificate mentions a His tag or a mass near 36 kilodaltons. A His tag is a run of histidine units added during manufacture so the protein can be pulled out of a bacterial soup, and the follistatin a human body makes does not have one. When two anti doping laboratories, at Seibersdorf and Cologne, bought seventeen black market products labelled follistatin 344, all nine that actually contained follistatin carried that tag along with oligomers, meaning copies stuck to one another. The catalogue format shows the same shape: ProSpec's His tagged version is 325 residues in total, of which ten are the tag, at 36.0 kilodaltons, sold for laboratory research use only. The other eight of the seventeen held no follistatin at all, and some held other growth promoting peptides instead, named as MGF and GHRP-2, so any certificate only describes the sample it was run on.
Reading gene therapy results as results for an injected protein, which is the substitution the sales copy depends on. Four things travel under this one name: a virus carrying the gene into muscle, a loop of bare DNA, an engineered follistatin Fc fusion built to stay where it is put, and a bacterial protein in a vial. Only the last one is what anybody buys, and it is the only one of the four with no human evidence I could find. The doses do not carry across either. Every dose in the gene therapy record is a count of gene carrying virus particles per kilogram of body weight, which does not convert into micrograms of protein. The two masses in the record point the opposite way: 50 to 200 milligrams of ACE-083 into a single muscle, which is 250 to 2,000 times the daily microgram convention, and a pharmaceutical model projecting 3 to 5 milligrams per kilogram a week for a half life engineered fusion, which is 240 to 400 milligrams a week for an 80 kilogram adult against a convention of roughly 0.7 to 1.4 milligrams a week.
What is known about harm
I found no safety record for the thing people inject. I found no repeat dose toxicology study, no carcinogenicity study and no genotoxicity study of injected follistatin protein in any species. What the anti doping laboratories found in the vials that did contain follistatin was a tagged, clumped, bacterial protein with none of the sugar coating the human version carries, which is the setup for an immune response against something the body already makes, and I found no measurement of anti follistatin antibodies in anybody injecting one. The endocrine worry was raised by the developers themselves, because follistatin suppresses follicle stimulating hormone. Those hormones stayed normal in the six men with Becker muscular dystrophy who received the gene in their thighs, which is a finding about six people given a virus rather than about repeated injections of a bacterial protein under the skin. And eight of the seventeen products bought held something other than follistatin, some of it other growth promoting peptides.