IGF-1 LR3 and MGF both sit in the IGF-1 pathway that drives muscle growth, but they act differently. IGF-1 LR3 is a long-acting, systemic IGF-1 analog; MGF (mechano growth factor) is a splice variant of IGF-1 released locally in response to muscle stress, studied for activating muscle repair cells. Both are unapproved research chemicals banned in sport.
At a glance
| IGF-1 LR3 | MGF | |
|---|---|---|
| Class | Long-acting IGF-1 analog | IGF-1 splice variant (mechano growth factor) |
| Action | Systemic, sustained IGF-1 signaling | Local muscle repair / satellite-cell activation |
| Duration | Long-acting (LR3 modification) | Short-acting (natural form) |
| FDA status | Not approved (research chemical) | Not approved (research chemical) |
| Human evidence | Limited | Limited / preclinical |
| Sport status | Banned (WADA) | Banned (WADA) |
The bottom line
Bottom line: Both target IGF-1 biology, but IGF-1 LR3 aims for broad, sustained systemic signaling while MGF is about local muscle repair. Neither has meaningful human outcome evidence for physique or performance, both are unapproved research chemicals, and both are prohibited in sport.
Frequently asked questions
What's the difference between IGF-1 LR3 and MGF?
IGF-1 LR3 is a long-acting systemic IGF-1 analog, while MGF is a splice variant of IGF-1 released locally in stressed muscle and studied for activating repair (satellite) cells. They act through related but distinct routes.
Do they build muscle?
Both are studied within the muscle-growth IGF-1 pathway, but robust human evidence for physique or performance benefit is lacking. Both are unapproved research chemicals.
Are they legal in sport?
No. IGF-1 analogs and related growth factors are banned at all times under the World Anti-Doping Agency code, and neither is FDA-approved.
References
Combined peer-reviewed sources from both peptide guides. Inclusion is not endorsement.
- Voorhamme D, Yandell CA. LONG R3IGF-I as a more potent alternative to insulin in serum-free culture of HEK293 cells. Mol Biotechnol. 2006. Peer-reviewed study
- Mongongu C, Coudore F, Domergue V, et al. Detection of LongR3-IGF-I and related analogs for antidoping purposes. Drug Test Anal. 2021. Peer-reviewed study
- Renehan AG, Zwahlen M, Minder C, et al. IGF-I, IGFBP-3, and cancer risk: systematic review and meta-regression analysis. Lancet. 2004. Peer-reviewed study
- Lu Z, Liu N, Huang H, et al. Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris. Appl Microbiol Biotechnol. 2023. Peer-reviewed study
- Hadsell DL, Parlow AF, Torres D, et al. Enhancement of maternal lactation performance during prolonged lactation in the mouse by mouse GH and long-R3-IGF-I is linked to changes in mammary signaling and gene expression. J Endocrinol. 2008. Peer-reviewed study
- Engel MG, Narayan S, Cui MH, et al. Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice. J Alzheimers Dis. 2025. Peer-reviewed study
- Hill M, Goldspink G. Expression and splicing of the IGF gene in rodent muscle is associated with muscle satellite (stem) cell activation following local tissue damage. J Physiol. 2003. Peer-reviewed study
- Yang S, Alnaqeeb M, Simpson H, Goldspink G. Cloning and characterization of an IGF-1 isoform expressed in skeletal muscle subjected to stretch. J Muscle Res Cell Motil. 1996. Peer-reviewed study
- Retraction: Mechano growth factor attenuates mechanical overload-induced nucleus pulposus cell apoptosis through inhibiting the p38 MAPK pathway. Biosci Rep. 2024. Peer-reviewed study
- Kandalla PK, Goldspink G, Butler-Browne G, et al. Mechano Growth Factor E peptide (MGF-E), derived from an isoform of IGF-1, activates human muscle progenitor cells and induces an increase in their fusion potential at different ages. Mech Ageing Dev. 2011. Peer-reviewed study
- Schlegel W, Raimann A, Halbauer D, et al. Insulin-like growth factor I (IGF-1) Ec/Mechano Growth factor--a splice variant of IGF-1 within the growth plate. PLoS One. 2013. Peer-reviewed study
- Li C, Vu K, Hazelgrove K, et al. Increased IGF-IEc expression and mechano-growth factor production in intestinal muscle of fibrostenotic Crohn's disease and smooth muscle hypertrophy. Am J Physiol Gastrointest Liver Physiol. 2015. Peer-reviewed study