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AMIRAVOResearch Library

Follistatin 344 vs IGF-1 LR3

Follistatin 344 and IGF-1 LR3 act on different pathways and have been studied in very different ways 1,7. FS344 is an alternatively spliced follistatin isoform used as a myostatin antagonist, and in humans it has been given only as a gene-therapy vector (rAAV1.CMV.huFollistatin344) injected into muscle in small trials 1,2,3. IGF-1 LR3 is a recombinant IGF-I fusion analogue created as a laboratory reagent, with no registered human study located 7,10. Anti-doping laboratories have analysed black-market material sold under both names and found His-tagged research-grade protein, and in the follistatin case frequent absence of the labelled substance 6,9.

Unbranded reference vial illustrating Follistatin 344; not an actual product
Follistatin 344
Not approved — research use only
Unbranded reference vial illustrating IGF-1 LR3; not an actual product
IGF-1 LR3
Not approved — research use only

Side by side

FieldFollistatin 344IGF-1 LR3
ClassMyostatin-binding protein (follistatin isoform FS344) 1Recombinant IGF-1 fusion analogue with reduced binding to IGF-binding proteins 7
Origin and structureAlternatively spliced follistatin cDNA whose product is a 315-amino-acid secreted peptide, chosen to avoid cell-surface binding and off-target effects 1Long [Arg3]-IGF-I: IGF-I with 11 N-terminal residues of methionyl porcine growth hormone plus Val-Asn and Arg replacing Glu-3, expressed in E. coli 7
Proposed mechanismAntagonises myostatin, which in preclinical species increased muscle size and strength 1Acts at the IGF-I receptor while binding poorly to IGF-binding proteins, which increased potency and duration in cells and animals 7,8
Half-lifeNot applicable as studied in humans: the gene-therapy approach produces sustained local expression rather than a dosed protein 1,2Not located; in pigs, variants including LR3-IGF-I suppressed plasma glucose far longer than native IGF-I (animal data) 8
Highest human trial phasePhase 1/2a gene therapy, completed: 6 patients with Becker muscular dystrophy, 6 with sporadic inclusion body myositis, and a 3-patient Duchenne study 2,3,4,5No registered study located (ClinicalTrials.gov searched 24 October 2026) 10
FDA statusNot FDA-approved in any form; follistatin is not named on the FDA compounding page as of 22 April 2026 12Not FDA-approved and not named on the FDA compounding page as of 22 April 2026 12. Recombinant IGF-1 itself is approved as mecasermin (INCRELEX, BLA 021839), a different molecule 11
Published human outcomesIn the Becker trial, 6-minute walk distance improved in 4 of 6 patients and was unchanged in 2, with histological changes reported 2; in the inclusion body myositis trial, annualised walk distance improved compared with matched untreated subjects 3None located 10
Safety signalsNo adverse effects were encountered in the Becker trial 2; a review notes theoretical concerns about follistatin suppressing follicle-stimulating hormone, which the FS344 approach was designed to avoid 1Not located for humans; the authors of the black-market analysis state that effects of His-tagged Long-R3-IGF-I in humans have not been described 9
WADA statusNamed under S4.3 as a myostatin-binding protein (follistatin); prohibited at all times (2026 List) 13Covered under S2.3, which names IGF-1 (mecasermin) and its analogues; prohibited at all times (2026 List) 13
Who funded the evidenceTrials were run by Nationwide Children's Hospital and Ohio State University investigators 2,3,4,5Australian CSIRO-linked academic groups developed and tested the analogues 7,8; the product analysis came from a German anti-doping laboratory 9

Follistatin 344: what the data says

Follistatin has been pursued in humans as a gene therapy rather than an injected protein. A review describes FS344 as an alternatively spliced isoform selected so that its 315-amino-acid secreted product avoids cell-surface binding sites, reducing off-target effects on the hypothalamic-pituitary-gonadal axis 1.

  • In a phase 1/2a trial in 6 patients with Becker muscular dystrophy (humans), vector was injected into both quadriceps; 6-minute walk distance improved in 4 patients and was unchanged in 2, with no adverse effects encountered 2.
  • In 6 patients with sporadic inclusion body myositis (humans), annualised 6-minute walk distance improved by 56 metres per year versus a decline of 25.8 metres per year in 8 matched untreated subjects 3.
  • A Duchenne muscular dystrophy study enrolled 3 participants and has posted results 5.
  • An anti-doping laboratory found that only 9 of 17 black-market products labelled follistatin actually contained it, with some instead containing MGF or GHRP-2, and all 9 containing His-tagged FS344 with oligomers 6.

IGF-1 LR3: what the data says

IGF-1 LR3 originated as a research reagent. In rat myoblasts and hepatoma cells (cell data), Long [Arg3]-IGF-I and related analogues were more potent than native IGF-I at stimulating protein and DNA synthesis 7.

  • In pigs and marmoset monkeys (animal data), variants with poor IGF-binding-protein affinity lowered plasma glucose 2- to 3-fold more potently than IGF-I and for substantially longer 8.
  • An anti-doping laboratory identified His-tagged Long-R3-IGF-I in a black-market vial and noted it is usually produced for biochemical studies, with human effects undescribed 9.
  • No registered human study was located 10. The approved IGF-1 product is mecasermin, a different molecule 11.

Key research differences

  • Pathway: FS344 antagonises myostatin 1, whereas IGF-1 LR3 acts at the IGF-I receptor 7.
  • How it has been given to humans: FS344 only as an AAV gene-therapy vector injected into muscle 2,3; IGF-1 LR3 not in any registered human study 10.
  • Human outcome data: FS344 gene therapy reported walk-distance changes in small completed trials 2,3; none were located for IGF-1 LR3 10.
  • Anti-doping classification: follistatin falls under S4.3 (myostatin inhibitors), IGF-1 analogues under S2.3 13.
  • Product identity problems: most follistatin black-market products tested did not contain the labelled substance 6, while the IGF-1 LR3 product tested was a His-tagged research-grade protein 9.

Where the evidence is limited

No study has compared FS344 and IGF-1 LR3. The human FS344 data come from unblinded gene-therapy trials with 3 to 6 participants per group and matched external comparators rather than randomised controls, and the intervention is a viral vector, not an injected peptide, so it does not describe what injected follistatin protein would do 2,3. IGF-1 LR3 has no human study at all, and its preclinical findings concern glucose and tissue growth in cells, pigs and marmosets 7,8,10. Analyses of illicit products under both names show the marketed material is often research-grade or not the labelled substance 6,9.

Frequently asked questions

Has follistatin 344 been given to people as a protein?
Not in the studies located. Human use has been as a gene therapy, rAAV1.CMV.huFollistatin344, injected into muscle in small completed trials 2,3,4.
Is there any human study of IGF-1 LR3?
No registered study was located on ClinicalTrials.gov 10. Published work is in cells, pigs and marmoset monkeys, plus one analysis of a black-market vial 7,8,9.
Can follistatin 344 and IGF-1 LR3 be compared directly?
No. They act on different pathways, and only follistatin has human data, from gene-therapy trials rather than protein administration 1,2,10.
What do anti-doping analyses say about products sold under these names?
Only 9 of 17 products labelled follistatin contained follistatin, all as His-tagged FS344, and some contained MGF or GHRP-2 instead 6. A vial sold as IGF-1 LR3 contained His-tagged Long-R3-IGF-I, a research reagent 9.

References

  1. Inhibition of myostatin with emphasis on follistatin as a therapy for muscle disease Muscle & Nerve. 2009
  2. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy Molecular Therapy. 2015
  3. Follistatin Gene Therapy for Sporadic Inclusion Body Myositis Improves Functional Outcomes Molecular Therapy. 2017
  4. Follistatin Gene Transfer to Patients With Becker Muscular Dystrophy and Sporadic Inclusion Body Myositis (NCT01519349) ClinicalTrials.gov. 2023
  5. Clinical Intramuscular Gene Transfer of rAAV1.CMV.huFollistatin344 Trial to Patients With Duchenne Muscular Dystrophy (NCT02354781) ClinicalTrials.gov. 2023
  6. Detection of black market follistatin 344 Drug Testing and Analysis. 2019
  7. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency Journal of Molecular Endocrinology. 1992
  8. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys Journal of Endocrinology. 1997
  9. Detection of His-tagged Long-R3-IGF-I in a black market product Growth Hormone & IGF Research. 2010
  10. ClinicalTrials.gov API search for "long R3" IGF (0 studies returned, 24 October 2026) ClinicalTrials.gov. 2026
  11. Drugs@FDA (openFDA) record for mecasermin (INCRELEX, BLA 021839, Ipsen) FDA openFDA. 2026
  12. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of 04/22/2026) FDA (Human Drug Compounding). 2026
  13. Prohibited List 2026 (in force 1 January 2026) World Anti-Doping Agency. 2026

For research use only. Not for human or veterinary use. Not a drug, food, or dietary supplement. This page compares published research and is not medical advice or a recommendation.