# Follistatin-344

Myostatin/activin-binding protein sold as 1 mg vials; about half of tested vials held no follistatin.

- Page: https://peprank.xyz/peptides/follistatin-344
- Category: Hormones & libido (Research peptide)
- Also known as: FS344; FST-344; 'F-344'; follistatin-315 (FS315); AAV1.FS344 / plasmid follistatin (gene therapy)
- Routes: Injection
- Safety tier: Strict: Avoid · Balanced: Avoid · Evidence only: Caution
- Risk axes (0 none to 3 severe): Seen harm 0, Mechanism 2, Data gap 3, Silent harm 3, Product 3
- Positive: 44% of 10 graded reports glowing or positive, shrunk toward the 49% all-report average by 8 reports' weight
- Rank: #46 of 61 research peptides
- Graded reports: 10 (Glowing 3, Positive 1, Nothing 3, Negative 2, Bad reaction 1)
- Evidence: Animal only — data for the protein alone; the only human data are 12 patients given intramuscular AAV1.FS344 gene therapy for muscle disease, which says nothing about injecting the protein
- Access: Grey market
- Onset: Unknown: there are no human pharmacokinetic data for injected follistatin protein. Users claim effects within days, which is not plausible for muscle growth.
- Lasts: Unknown for the protein (users quote anything from 90 minutes to 12 hours); gene therapy is designed to last months or longer.
- Cost per month: ≈ €180–450 (researchers' estimate)
- Updated: 2026-10-30

**Why Avoid under the strict bar:** Blocks myostatin and activin signalling (FSH axis, angiogenesis, glucose) with no human safety data for the injected protein; vials often hold other drugs.

## What users report

Eleven reports: eight on grey-market vials and three on offshore gene therapy. The four glowing or positive vial reports (10 lb in 20 days, a 40 lb deadlift jump in a week, 'super soldier serum') all come from people also on testosterone, tesamorelin/ipamorelin or a hard training block, or describe gains too fast to be muscle. The others get sore, swollen injection sites lasting days, flu-like symptoms, fatigue and fog, or nothing. Replies in these threads overwhelmingly call it a waste of money. Of three gene-therapy patients (offshore clinics in Mexico and Honduras; one paid $25,000), two noticed nothing and one, who gave no details, called the results impressive. Felt nothing: Of 8 reports on the vials, 1 says it does nothing and 3 describe only injection-site or flu-like reactions; 2 of 3 gene-therapy reports felt nothing..

**Effects:** claimed strength and 'pump' (confounded by steroids, GH secretagogues and training); muscle growth in animal and gene-therapy studies

**Downsides:** swollen, painful injection-site lumps lasting days; flu-like symptoms, fatigue and mental fog; very expensive per mg; no measurable effect for many users

**Risks:** Product: in an anti-doping lab test only 9 of 17 black-market 'follistatin 344' vials contained follistatin; some held GHRP-2 or mechano growth factor instead (Reichel 2019); Activin/FSH axis: follistatin neutralises activin, which drives pituitary FSH; mice overexpressing it have reproductive defects; Angiogenic in vivo (rabbit cornea), strongly so together with bFGF: a theoretical route to feeding tumour vessels; Higher circulating follistatin tracks with type 2 diabetes, heart failure and death in a 4,733-person cohort (association, not proof); A related myostatin/activin trap, ACE-031, was halted in a pediatric trial for nosebleeds and telangiectasias

**Caveat:** FS344 is a roughly 38 kDa protein isoform (the precursor of circulating FS315), not a short peptide; whether a lyophilised research vial holds intact, active protein is unverified, and the anti-doping test found many held none. The gene-therapy results come from muscle-disease patients and a different delivery, and the offshore clinics' own outcome data are unpublished or self-reported.

**Typical use:** Users: 50-100 mcg/day subq or IM for 10-20 days, some up to 1 mg/day. No human dose has been studied for the protein.

**Getting it:** Sold as 1 mg 'research' vials of recombinant, mostly E. coli-made protein; never approved. Plasmid follistatin gene therapy is offered at offshore clinics (Próspera and Roatán in Honduras, Mexico) for about $25,000. WADA-prohibited (S4.3); gene doping is banned separately.

**Stacked with:** Testosterone and other anabolic steroids (Most glowing reports come from people on TRT or a steroid cycle, so the steroid explains the gain.); Tesamorelin / ipamorelin or IGF-1 LR3 (Run alongside GH secretagogues or IGF-1 LR3 in 10-20 day 'myostatin' blocks.)

## Risk profile

- **Seen harm 0/3:** No published case reports, regulator warnings or trial SAEs for injected follistatin protein; the 12 muscle-disease patients given AAV1.FS344 gene therapy had no reported adverse effects. Reddit reports are swollen, painful injection sites lasting days, flu-like symptoms and fatigue, which are not serious by the rubric. The zero reflects essentially no documented exposure, not reassurance.
- **Mechanism 2/3:** Credible pathways from its targets: it neutralises myostatin and activin, which suppresses pituitary FSH (hormone axis), and recombinant follistatin is angiogenic in the rabbit cornea, strongly so with bFGF (vessel growth in animals). A related ligand trap, ACE-031, caused nosebleeds and telangiectasias that stopped its pediatric trial, and higher circulating follistatin tracks with diabetes and mortality in a cohort study. Transgenic overexpression causes reproductive defects in mice, but that is lifelong genetic exposure rather than use exposure, so this stays at 2, not 3.
- **Data gap 3/3:** No human safety data for the product sold, recombinant (mostly E. coli-made, His-tagged) follistatin injected subcutaneously. The only human exposure is intramuscular AAV1 gene therapy in 12 patients with muscle disease and unpublished offshore plasmid treatments, which differ in delivery, dose and duration and do not bridge to the vials.
- **Silent harm 3/3:** The angiogenic pathway points at theoretical support for tumour vessels, which is silent and delayed (3 under the rubric). Fertility and glucose effects would build up but show on hormone or glucose tests (a 2); injection-site and flu-like reactions are immediate.
- **Product 3/3:** Grey-market injectable vials. An anti-doping laboratory found follistatin in only 9 of 17 black-market 'follistatin 344' products; the rest held other growth-promoting peptides such as MGF or GHRP-2, and all genuine samples were His-tagged recombinant protein with heavy oligomerisation. Users describe swollen, painful injection sites lasting days.
- **Never if:** Pregnancy, breastfeeding or trying to conceive (follistatin suppresses FSH; overexpressing mice have reproductive defects); Active or past cancer (angiogenic in vivo); Diabetes or prediabetes; Under 18

## Top reports

- Glowing, recovery, 100 mcg/day: “10 pounds of lean muscle in 20 days. Only lost 2 of them. And im a hard gainer as F.” — [r/Biohackers](https://www.reddit.com/r/Biohackers/comments/1iqvast/follistatin344/oec5raz/)
- Glowing, recovery: “ive started follistatin 344 around a week and a half ago and i honestly have seen huge changes” — [r/Biohackers](https://www.reddit.com/r/Biohackers/comments/1iqvast/follistatin344/oongdjd/)
- Glowing, recovery: “344 merk ik veel spiergroei en herstel. Heb nooit spierpijn en het is alsof ik op een “super soldier serum” ben zeggen me vrienden.” — [r/Testosterone](https://www.reddit.com/r/Testosterone/comments/1wqcgvo/running_500mgs_test_subq_with_follistatin_344/pc2zxsl/)
- Positive, recovery, 100 mcg/day for 10 days: “I did 100mcg/day for 10 days. Injected into abdomen w insulin needle. Yes I put on about 5lbs of lean mass over 5 weeks.” — [r/BodyHackGuide](https://www.reddit.com/r/BodyHackGuide/comments/1q2njfd/igf1_lr3_follistatin_344_gh_morning_test_nppdeca/o852o9c/)
- Nothing, longevity: “I did my Follistatin 344 gene therapy at Roatan with Dr.Terry it’s been 3 months for me now since, but I haven’t noticed any effects yet.” — [r/Biohackers](https://www.reddit.com/r/Biohackers/comments/18o0nz1/follistatin_344_plasma_gene_therapy_anyone_tried/mbjp8ag/)

## Studies

- [Lee & McPherron 2001: regulation of myostatin activity and muscle growth](https://pubmed.ncbi.nlm.nih.gov/11459935/) (animal, 2001): Follistatin blocked myostatin binding to the ActRIIB receptor, and mice overexpressing it in skeletal muscle had dramatic increases in muscle mass.
- [Mendell et al. 2015: phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy](https://pubmed.ncbi.nlm.nih.gov/25322757/) (open-label, n=6, 2015): AAV1.FS344 injected into both quadriceps: 4 of 6 patients walked 29-125 m farther in 6 minutes, 2 did not improve; no adverse effects; biopsies showed less fibrosis.
- [Mendell et al. 2017: follistatin gene therapy for sporadic inclusion body myositis](https://pubmed.ncbi.nlm.nih.gov/28279643/) (controlled, n=14, 2017): Six treated patients with an exercise programme gained a median 56 m/year on the 6-minute walk while eight matched, non-randomised controls lost 25.8 m/year (p = 0.01).
- [Reichel et al. 2019: detection of black-market follistatin 344](https://pubmed.ncbi.nlm.nih.gov/31758732/) (in-vitro, n=17, 2019): Only 9 of 17 products labelled follistatin contained it, all as His-tagged FS344 with heavy oligomerisation; others held growth-promoting peptides such as MGF or GHRP-2.
- [Kozian et al. 1997: follistatin regulates autocrine endothelial activity and induces angiogenesis](https://pubmed.ncbi.nlm.nih.gov/9042163/) (animal, 1997): Recombinant follistatin made human endothelial cells proliferate and was angiogenic in the rabbit cornea, strongly so combined with bFGF.
- [Guo et al. 1998: overexpression of mouse follistatin causes reproductive defects in transgenic mice](https://pubmed.ncbi.nlm.nih.gov/9440814/) (animal, 1998): Mice engineered to overproduce follistatin developed reproductive defects, consistent with its suppression of activin and FSH.
- [Elevated circulating follistatin associates with increased risk of mortality and cardiometabolic disorders (Malmö cohort, 2023)](https://www.nmcd-journal.com/article/S0939-4753(23)00371-X/fulltext) (observational, n=4733, 2023): Over about 22 years, higher plasma follistatin was associated with more deaths, heart failure, stroke, coronary events and kidney disease, partly through diabetes.
- [Campbell et al. 2017: myostatin inhibitor ACE-031 in boys with Duchenne muscular dystrophy](https://pubmed.ncbi.nlm.nih.gov/27462804/) (rct, 2017): A related decoy-receptor approach to the same ligands was stopped early for nosebleeds and telangiectasias, with only trends toward lean-mass gain.

## Sources

- [WADA: detection of follistatin doping in urine and blood (most black-market products are E. coli-expressed)](https://www.wada-ama.org/en/resources/scientific-research/detection-follistatin-doping-urine-and-blood)
- [WADA 2026 Prohibited List, S4.3 (myostatin-binding proteins, e.g. follistatin)](https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf)
- [MIT Technology Review 2023: Minicircle tests follistatin gene therapy in Próspera, Honduras](https://www.technologyreview.com/2023/02/13/1068330/minicircle-prospera-honduras-biohacking-follistatin-gene-therapy/)
- [Fortune 2023: Bryan Johnson's $25,000 follistatin gene therapy on Roatán](https://fortune.com/2023/12/21/bryan-johnson-human-guinea-pig-unproven-tests-reprogram-human-genes-follistatin-roatan-island-honduras/)
- [Superpower peptide guide: Follistatin-344 (summary of the gene-therapy evidence)](https://superpower.com/guides/peptides/follistatin-344)