Follistatin 344 is sold by two of the four vendors we review and described on ranking pages as a myostatin blocker. The human studies that use the name are of three different kinds, and none tests a vial of protein. We read the abstracts and the two vendor listings to sort them out. Peptryn and American Peptides do not list it ( for the latter). This is not advice to use anything, and vendors label it for laboratory research only.
What follistatin is
Follistatin is a protein that blocks several members of the TGF-beta family, including myostatin, a negative regulator of muscle growth. A 2009 mouse study found that overexpressing it raised muscle weight by about 37% in control animals, and by the same amount in mice with no myostatin gene, which suggests myostatin is not the only target. The authors' results point to activin, another protein it binds, as a possible contributor. Our post on myostatin inhibitors covers the drug trials built on the same idea.
The two vendors disagree on what 344 means. Core Power Peptides calls it the primary circulating isoform (). Peptides for Sale calls it the 344 amino acid precursor and says processing yields the circulating FS-315 isoform. A gene therapy paper describes FS344 as an alternatively spliced form chosen to avoid binding off-target sites. We could not settle the question from the sources we read.
What has been tested in people
Swipe the table sideways to see every column.
| Study | What was given | Who | What the abstract reports |
|---|---|---|---|
| Becker muscular dystrophy, 2015 | Gene therapy: a virus carrying the FS344 gene, injected into the thigh muscles | 6 patients | Six minute walk improved in four (by 29 to 125 m) and did not change in two. No adverse effects were reported. Tissue showed less fibrosis. |
| Inclusion body myositis, 2017 | The same kind of gene therapy | 6 treated, 8 untreated comparison patients | Walk distance rose 56.0 m a year against a 25.8 m decline. A later commentary in the same journal disputes the functional claims. |
| ACE-083 in healthy women, 2018 | A follistatin-based protein injected into one muscle | 58 postmenopausal women | Muscle volume in the injected muscle rose by up to 14.5% and 8.9% in two muscles. No significant change in strength. |
| ACE-083 in Charcot-Marie-Tooth disease, 2022 | The same protein, injected into a lower leg muscle | 44 treated in the randomized part | Muscle volume 13.5% greater than placebo. Functional outcomes did not significantly improve. |
| ACE-083 in facioscapulohumeral dystrophy, 2022 | The same protein, injected into the biceps or a lower leg muscle | 55 evaluable adults | Muscle volume 16.4% and 9.5% greater than placebo. No consistent improvement in function. |
Why none of this tests a vial of follistatin
The gene therapy studies delivered a gene, so the muscle made its own follistatin. ACE-083 is a different molecule, a follistatin-based therapeutic that is injected into a chosen muscle. The largest muscle volume numbers belong to ACE-083, and the two disease trials found no consistent gain in function alongside them. We found no published human trial of follistatin 344 protein as a research vendor lists it.
What the vendors list
Core Power Peptides lists a 1 mg follistatin 344 vial that it says is third-party tested to 99% or higher purity, with a COA provided and no lab named (). Peptides for Sale lists a 1 mg vial at 99% or higher by HPLC and says a certificate of analysis is available for each batch (). Peptryn lists none. We read no certificate for either. Peptides for Sale also lists ACE-031, which our myostatin post covers, and describes its follistatin as a reference compound for mouse studies.
Our guide to reading a COA explains what to look for, and the reviews of Core Power Peptides and Peptides for Sale list what we could not confirm for each.
Sports status
The Cologne anti-doping laboratory says WADA has banned myostatin inhibition since 1 January 2008, and USADA's summary of the 2019 list shows the category covering myostatin-binding proteins and agents that block the activin receptor. The vendors describe follistatin as binding myostatin, which would place it inside that wording. We did not find the list naming follistatin in a source we could read, so tested athletes should read the current list themselves.
Frequently asked questions
What is follistatin 344?
A form of follistatin, a protein that binds myostatin and activin. The vendors we read disagree on whether 344 is the circulating form or a precursor, and we could not settle it.
Has follistatin been tested in people?
Follistatin gene therapy has been tried in six-person groups, and a follistatin-based protein, ACE-083, has been injected into single muscles. We found no human trial of follistatin 344 protein as sold in a vial.
Did muscle volume gains bring better function?
Not consistently. In the two ACE-083 disease trials, muscle volume rose significantly while functional measures did not improve consistently.