Section 01
What it's used for
Whole-body muscle effects
Unlike natural MGF, which must be injected into a muscle, PEG-MGF is modified to spread through the body after injection, so it is being studied for whole-body muscle-building effects rather than effects at one injection site.
▸Clinical wording
PEG-MGF enables systemic administration for whole-body muscle anabolic effects, unlike native MGF which requires local injection.
Muscle-wasting conditions
Researchers are studying PEG-MGF for conditions causing body-wide muscle loss: age-related loss (sarcopenia), illness-related wasting (cachexia), and muscle diseases (myopathies), where injecting one muscle at a time is impractical.
▸Clinical wording
Research for systemic treatment of sarcopenia, cachexia, and myopathies where local injection is impractical.
Recovery after exercise damage
PEG-MGF is being studied for helping muscles recover after exercise-related damage, through activating satellite cells, the muscle's own repair cells, throughout the body rather than only at the site of an injury or injection.
▸Clinical wording
Studied for recovery from exercise-induced muscle damage through systemic satellite cell activation.
Section 02
Mechanism of Action
An alternative reading of a growth gene
- MGF is an alternative version of the growth factor gene (IGF-1) carrying a different tail segment.
- In rodent muscle, local damage changed how that gene was read, alongside activation of muscle stem cells.
- PEG-MGF is a synthetic copy of that tail segment with a polyethylene glycol group attached.
- Its presumed biology is inherited entirely from studies of the unmodified tail peptide.
▸Clinical wording
MGF as a mechanically induced IGF-1 splice variant
MGF is the name given to a splice variant of the IGF-1 gene (IGF-1Ec in humans, IGF-1Eb in rodents) whose distinguishing feature is an alternative C-terminal E domain. Hill and Goldspink showed in rodent muscle that local tissue damage alters splicing of the IGF-1 gene and that this shift is associated with activation of muscle satellite (stem) cells during repair (Journal of Physiology, 2003). PEG-MGF is a synthetic peptide corresponding to that E domain with a polyethylene glycol group attached, so its presumed biology is inherited entirely from work on the unmodified E-domain peptide.
Effects seen in muscle cell cultures
- In muscle cell culture the tail peptide increased cell division while blocking final maturation.
- That is the opposite of what mature IGF-1 does in the same cells.
- The effect persisted when the IGF-1 receptor was blocked, which the authors read as a separate receptor.
- In human muscle progenitor cells it extended proliferative life span, with the effect diminishing in older donors.
▸Clinical wording
E-domain peptide effects on myoblasts and satellite cells
Yang and Goldspink reported that in myoblast culture the MGF E domain increased proliferation while inhibiting terminal differentiation — the opposite of mature IGF-1 — and that the effect persisted when the IGF-1 receptor was blocked with antibodies, which they read as evidence for a separate receptor (FEBS Letters, 2002). Kandalla and colleagues treated primary human muscle progenitor cells from donors of different ages and found that MGF-E significantly increased proliferative life span and delayed senescence in cells from neonatal and young adult donors, with the effect diminishing in older donors (Mechanisms of Ageing and Development, 2011).
The proposed mechanism failed replication
- Another group found the peptide's signalling and growth effects in muscle cells did depend on the IGF-1 receptor.
- The peptide raised one signalling marker dose-dependently but did not activate the receptor on its own.
- Instead it increased the receptor's availability at the cell surface by roughly 40%.
- An independent industry group found no increase in cell proliferation at concentrations up to 500 ng/ml.
▸Clinical wording
Contested receptor mechanism and failed replication
The receptor-independent claim has not held up uniformly. Brisson and Barton found in C2C12 myoblasts and IGF-1R-overexpressing fibroblasts that E-peptide signalling, mitogenic and motogenic effects were dependent on the IGF-1 receptor: E-peptides raised ERK1/2 phosphorylation dose-dependently but did not activate the receptor alone, instead increasing its cell-surface availability by roughly 40%, while Akt was unchanged (PLoS ONE, 2012). An independent industry group later reported that synthetic MGF peptide at up to 500 ng/ml failed to increase proliferation of C2C12 cells or primary human skeletal muscle myoblasts (Fornaro et al., AJP-Endocrinology and Metabolism, 2014).
Nobody has isolated the natural peptide
- A review noted that no such peptide product has been isolated from cells, culture medium, tissue or body fluids.
- The evidence base rests largely on messenger RNA splice-variant measurements and on synthetic peptides.
- The authors warn that extrapolating messenger RNA data to protein-level action needs extreme care.
- Whether a distinct MGF peptide is produced and acts in the body remains unestablished.
▸Clinical wording
Uncertain existence of the endogenous peptide
Matheny and colleagues reviewed the field and noted that no analogous peptide product of the Igf1 gene has been identified in or isolated from cultured cells, their conditioned medium, or in vivo animal tissues or biological fluids (Endocrinology, 2010). The MGF evidence base rests largely on mRNA splice-variant measurements and on synthetic peptides, and the authors caution that extreme care is needed when extrapolating mRNA data to actions at the protein level. Whether a distinct MGF peptide is produced and acts in vivo therefore remains unestablished.
What the attached polymer changes
- No peer-reviewed study of PEG-MGF itself could be located, so the polymer's role is inferred from PEGylated IGF-1.
- In 62 healthy volunteers, PEGylated IGF-1 lasted 140-200 hours and suppressed growth hormone far less.
- Researchers state the trade-off plainly: a longer half-life frequently costs biological activity.
- Their PEGylated conjugate showed altered binding, proliferation and uptake until the linker was cleaved.
▸Clinical wording
PEGylation effects inferred from PEGylated IGF-1
No peer-reviewed study of PEG-MGF itself could be located, so the contribution of the PEG group is inferred from PEGylated IGF-1. In a first-in-man study in 62 healthy volunteers, PEGylated rhIGF-1 showed a half-life of 140-200 hours and a much weaker suppression of growth hormone than unmodified rhIGF-1 (Kletzl et al., Growth Hormone & IGF Research, 2017). Braun and colleagues state the trade-off directly: PEGylation increases half-life but frequently comes at the cost of reduced bioactivity, and their PEGylated IGF-1 conjugate showed altered binding-protein affinity, cell proliferation and endocytosis until the linker was cleaved (Journal of Controlled Release, 2018).
Section 03
Biological Pathways
- MGF splice-variant originLocal muscle damage shifts IGF-1 gene splicing toward MGF, a variant whose appearance accompanies activation of muscle satellite (stem) cells during repair in rodent studies (Hill and Goldspink, 2003).
- Proliferation over differentiationIn myoblast culture, the MGF E domain raised proliferation while inhibiting differentiation, opposite to mature IGF-1, and this persisted with the IGF-1 receptor blocked (Yang and Goldspink, 2002).
- Contested IGF-1R dependenceA later study found E-peptide mitogenic signaling was IGF-1R dependent, raising ERK1/2 and receptor surface availability, while a separate test found no proliferation increase (Brisson 2012; Fornaro 2014).
- PEGylation pharmacokineticsNo study of PEG-MGF exists; PEGylated IGF-1 shows the trade-off, extended half-life to 140-200 hours via reduced renal clearance but weakened bioactivity and GH suppression (Kletzl 2017; Braun 2018).
Section 04
Dosage Information
PEGylated YQPPSTNKNTKSQRRKGSTFEEHK| Route / system | Context | Range studied | Limitation |
|---|---|---|---|
| Subcutaneous / intramuscular | Bodybuilding practice after training, in a 2026 review | 200–400 µg 2–3 times a week — about 2–6 µg/kg for a 70–90 kg adult; loading 100 → 200 → 300 µg over 8 weeks, cycles of 8–16 weeks | The review that collected these numbers ranks the evidence lowest: no peer-reviewed human study reports even the route it is given by, let alone an effect. |
| Intramuscular — mouse injury model | Bruised mouse muscle — MGF without PEG, not this molecule | 5 µg in 20 µl into each calf muscle on the day of injury and days 1 and 2. No live animal of any species has had the PEGylated form. | The same microgram figure does not cover both forms: adding PEG changes how fast it clears and where it goes, and this went into the injured muscle itself. |
| Subcutaneous — fate in the body | The PEGylated form, in any species, humans included | Nothing measured: no half-life, no peak level, no share reaching the blood. The 2026 review lists the half-life as not reported. | PEG was added to fix a half-life of minutes, and dosing twice a week assumes it worked. The "several days" sellers quote was never measured in any species. |
Results
Syringe Fill Level (100u syringe)
Set positive values for: Recommended dose per kg.
Research Use Only. This information is for educational and research purposes only. Not intended for medical advice or self-medication.
Section 05
Protocols
- Protocol 01
IGF-1 LR3 + PEG-MGF Advanced Stack
Maximum muscle growth stack combining systemic IGF-1 with localized MGF for hypertrophy and repair.
- Focus
- Sport & Performance
- Level
- Advanced
- Duration
- 6–8 weeks
Section 06
Stability & Storage
Lyophilised powder
The lyophilised powder is stored at −20 °C for 12–18 months. PEG protection makes it more stable than native MGF, and it is reconstituted with bacteriostatic water before use.
After reconstitution
Once reconstituted, the solution is kept at 2–8 °C and used within 21 days. Refrigeration between doses helps maintain the peptide's stability.
Section 07
Side Effects & Precautions
Similar profile to MGF with potential additional PEG-related effects: injection site irritation, potential anti-PEG antibody development with chronic use. Hypoglycemia risk. Limited human safety data.
Section 08
Regulatory Status
It remains a research peptide: no approved label, indication, dose or established human safety profile exists for it.
FDA / United States
Not approved
In 2023 the FDA assigned PEG-MGF to Category 2 of the interim 503A bulk-substances list over safety concerns and lifted that listing in April 2026 when the nomination was pulled for further review; a fresh Pharmacy Compounding Advisory Committee hearing is scheduled before the end of February 2027. Removal from Category 2 is not addition to the 503A Bulks List — PEG-MGF is not on that list, so no lawful compounding route is open.
EU / EMA
Not approved
PEG-MGF has no EU marketing authorisation and does not appear among medicines evaluated by the CHMP.
WADA
Prohibited under S2
As an IGF-1-related growth factor, PEG-MGF falls under category S2 (Peptide Hormones, Growth Factors and Related Substances) — banned at all times, in and out of competition, with no therapeutic-use exemption.
Clinical trials
No completed human trial exists
The pegylation extends the half-life seen in animal models, but no dose-ranging, safety or efficacy study in humans has been published.
A «research use only» label does not turn PEG-MGF into an approved medicine and says nothing about its purity. Regulatory status differs between jurisdictions and changes over time — check the current documents of your own regulator before relying on any of this.
Section 09
Research Studies
- [1]Expression and splicing of the insulin-like growth factor gene in rodent muscle is associated with muscle satellite (stem) cell activation following local tissue damageHill M, Goldspink G. · The Journal of Physiology · 2003
- [2]Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiationYang SY, Goldspink G. · FEBS Letters · 2002
- [3]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 agesKandalla PK, Goldspink G, Butler-Browne G, Mouly V. · Mechanisms of Ageing and Development · 2011
- [4]Insulin-like growth factor-I E-peptide activity is dependent on the IGF-I receptorBrisson BK, Barton ER. · PLoS ONE · 2012
- [5]Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cellsFornaro M, Hinken AC, Needle S, et al. · American Journal of Physiology-Endocrinology and Metabolism · 2014
- [6]Minireview: mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regenerationMatheny RW Jr, Nindl BC, Adamo ML. · Endocrinology · 2010
- [7]First-in-man study with a novel PEGylated recombinant human insulin-like growth factor-IKletzl H, Guenther A, Höflich A, et al. · Growth Hormone & IGF Research · 2017
- [8]Bioresponsive release of insulin-like growth factor-I from its PEGylated conjugateBraun AC, Gutmann M, Mueller TD, Lühmann T, Meinel L. · Journal of Controlled Release · 2018
- [9]PEGylation, successful approach to drug deliveryVeronese FM, Pasut G. · Drug Discovery Today · 2005
Section 10
Frequently Asked Questions
The core mechanism is contested rather than confirmed. One line of research reports the MGF E-domain drives myoblast proliferation independently of the IGF-1 receptor, but a separate group found the effect was IGF-1-receptor-dependent after all, and an industry study found synthetic MGF peptide had no effect on myoblast proliferation at concentrations up to 500 ng/ml. No published study has tested PEG-MGF, the PEGylated form itself, in any animal or person.
This has never been measured for the PEGylated peptide in any species. A 2026 review that collects self-administration protocols lists PEG-MGF's half-life as 'not reported' — no peak level, no half-life, no share of a dose reaching the blood has been published for this molecule.
Native MGF clears from the bloodstream within minutes, so it has to be injected directly into the target muscle. Adding a polyethylene glycol chain is meant to slow that clearance so the peptide can be given under the skin and reach muscle throughout the body instead of just at the injection site. That extended half-life for the PEGylated form has never actually been measured in an animal or a person.
Self-administration protocols collected in a 2026 review describe 200 to 400 µg two to three times a week, roughly 2 to 6 µg/kg, often with a loading pattern rising from 100 to 300 µg over eight weeks. The review ranks this evidence at its lowest tier: no peer-reviewed human study reports even the route it's given by, let alone measures an effect from it.
Human safety data are limited. Reported effects mirror plain MGF plus PEG-specific concerns: injection-site irritation, possible anti-PEG antibody formation with repeated dosing, and a theoretical hypoglycemia risk tied to IGF-1-axis activity.
Yes. PEG-MGF is classed as an IGF-1-related growth factor, and that category is prohibited by WADA under S2 at all times, in and out of competition — unlike GLP-1-type incretin drugs, which sit in a different, non-prohibited category.
The lyophilised powder is kept at −20 °C, where it's estimated to stay stable for 12 to 18 months; PEGylation reportedly makes it more stable than unmodified MGF. Once reconstituted with bacteriostatic water, the solution is kept at 2–8 °C and used within 21 days.