activin/myostatin-binding glycoprotein precursor; gene-therapy transgene in clinical studies

Follistatin-344

aka FST-344 · FS344 · FST344 · follistatin 344 precursor

Evidence grade
Grade D: Preclinical only
for injected protein for muscle growth
User score too few reports (9) needs ≥ 10 reports
US FDA Not approved checked 2026-11-13
WADA 2026 Prohibited (S4.3) at all times · checked 2026-11-13
EU No data · checked 2026-11-13

Goals: Recovery & injury · Muscle & strength Compare with another peptide →

User reports

approximate — combined from two independent Reddit reads

Men 45–60

0 men aged 45–60

No reports in this group yet.

All men

0 men

No reports in this group yet.

Everyone

9 people

small sample · n = 9

Outcome positive 5 of 9 · unclear 3 of 9 · mixed 1 of 9 · no effect 1 of 9

Benefits muscle 4 of 9 · strength 2 of 9 · other 1 of 9

Side effects none reported

Why stopped cost 2 of 9 · other 1 of 9

Stopped 4 of 9 Used with other compounds 0 of 9

User reports are anecdata, not evidence: self-selected, unverified, often combined with other compounds.

In their words

  • “definite, but modest effect on building muscle”

  • “I tried it for a week. I definitely felt the effect. I stopped out of fear of heart enlargement.”

  • “couldn't tell anything from the other two”

  • “Had a definate, but modest effect on building muscle. I was advised that I should continue cycle for 12 weeks.”

  • “I tried it for a week, but in the end I was too afraid of messing up my heart to continue.”

  • “100mcg daily. 20days cycle. The pump is insane. You became so strong that you need to be careful.”

Read summaries and method notes

Read 1. No verified man aged 45–60 (n=0). Three firsthand users: one reported a modest muscle-building effect over five weeks (stopped because of cost, no side effects on bloodwork), one felt an effect but stopped after a week for fear of heart enlargement, one noticed nothing from Follistatin-344/315. Follistatin gene-therapy reports were excluded as a different modality. Evidence is extremely sparse and product quality was repeatedly questioned.

Read 2. No man aged 45–60 or stated man (an 82-year-old gene-therapy report is a third-party summary, not a peptide self-report). Eight users: 5 positive for muscle (4) and strength (2) — a stronger pump and muscle gain within 2–20 days, or modestly fuller muscles over 5 weeks — and 3 unclear early or abandoned reports. Nobody reported physical side effects; three stopped early (two for cost of about $155/week or up to $1,800 for 3 months, one after a week for fear of heart risks). Recurring warnings about ineffective cheap products.

Note 1. Very sparse firsthand peptide use. Follistatin-344 gene-therapy reports were excluded because the delivery modality is materially different. No verified age/sex-qualified men.

Note 2. No explicit age/sex in the self-reports. Two threads covered minicircle/plasmid gene therapy without firsthand reports; r/PeptideSelect was excluded. Three seed threads were not available.

Each read counted people independently. Overlap between the two reads is estimated from shared threads and removed; counts are approximate. How we count.

Summary

344-amino-acid glycoprotein isoform of endogenous follistatin. Potent antagonist of the TGF-β superfamily — primarily myostatin and activin A. Converts in vivo to circulating FS-315. Sequesters ligands such as activin, reducing downstream ActRIIB/Smad2/3 signalling. The small AAV-FS344 gene-transfer studies are early, nonrandomized disease studies; efficacy does not transfer to injected protein. A sarcopenia study examined declining levels, not a therapeutic intervention, and did not associate baseline levels with acute sarcopenia. Experimental gene transfer is investigational, not an approved off-label treatment.

Safety

  • Published central serous chorioretinopathy case series after reported injected follistatin-344
  • Small gene-transfer cohorts do not establish injectable-protein or long-term safety
  • Gonadal hormones remained normal in the small AAV trials; FSH suppression was not demonstrated there
  • Cancer, reproductive and cardiovascular risks of enhancement use remain unquantified
  • Mouse lifespan claim comes from a paper retracted in 2025

From labels, regulators and trials. No signal in small studies ≠ safe.

Evidence D injected protein for muscle growth

D stands. The only human efficacy data are two 6-person open-label AAV gene-transfer studies in muscle disease - a different intervention from injecting the protein. The one human report on the injected product is an 11-case eye-disease (central serous chorioretinopathy) series.

Human trials · 3

  1. PMID 253227572015open-label phase 1/2a dose-escalation gene-transfer study 6 people

    ambulatory men with Becker muscular dystrophy

    AAV1-FS344: four participants improved 6-minute walking distance by 29–125 m; no randomized control and no established relevance to injected protein. Source

  2. PMID 282796432017open-label gene-transfer study with exercise and 8 nonrandomized untreated comparators 6 people

    sporadic inclusion body myositis

    Median annualized 6-minute walk change +56.0 m versus -25.8 m in untreated comparators; exercise and nonrandomized design limit attribution. Source

  3. PMID 326715992020retrospective adverse-event case series, not an efficacy trial 11 people

    male bodybuilding athletes reporting high-dose subcutaneous follistatin-344

    Central serous chorioretinopathy after exposure; recurrent disease in three with repeated exposure; incidence and causality not established. Source

Bar length = trial size on a log scale.

Dose ranges

Reported ranges from labels and studies, with context. Not a recommendation.

  • clinical trial — AAV1 gene transfer, not protein injection
    3 × 10^11–6 × 10^11 vector genomes/kg/leg, delivered to quadriceps in the Becker muscular dystrophy study Source

Editorial ratings EDITORIAL

Editors’ judgement, 0–5. Opinion, not data; separate from grade and user score.

  • Safety 2 out of 5
  • Sleep 2 out of 5
  • Recovery 3 out of 5
  • Cognitive 1.5 out of 5

Sources

  1. pubmed.ncbi.nlm.nih.gov/25322757/
  2. pmc.ncbi.nlm.nih.gov/articles/PMC5383643/
  3. pubmed.ncbi.nlm.nih.gov/32671599/
  4. accessdata.fda.gov/scripts/opdlisting/oopd/detailedIndex.cfm?cfgridkey=369612
  5. wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf
  6. pmc.ncbi.nlm.nih.gov/articles/PMC4426808/
  7. pubmed.ncbi.nlm.nih.gov/16198295/
  8. pubmed.ncbi.nlm.nih.gov/35537048/
  9. pubmed.ncbi.nlm.nih.gov/40789040/
  10. pmc.ncbi.nlm.nih.gov/articles/PMC12377719/
  11. pubmed.ncbi.nlm.nih.gov/22052313/
  12. fda.gov/advisory-committees/advisory-committee-calendar/july-23-24-2026-meeting-pharmacy-c
  13. wada-ama.org/sites/default/files/resources/files/research_19c09cr.pdf
  14. pmc.ncbi.nlm.nih.gov/articles/PMC2852878/
  15. pmc.ncbi.nlm.nih.gov/articles/PMC2393740/
  16. pmc.ncbi.nlm.nih.gov/articles/PMC8225567/
  17. pubmed.ncbi.nlm.nih.gov/33964607/
  18. clinicaltrials.gov/study/NCT01519349
  19. fda.gov/media/94155/download

Reddit threads read · 9

6 further sources on commercial or non-primary hosts not listed.

Research checked 2026-11-13.