PEG-MGF

updated

PEG-MGF is the pegylated form of synthetic mechano growth factor, a peptide matching the 24 most C-terminal residues of the IGF-IEb splice variant. The splice variant is real and its expression in muscle rises with lifting, but a PubMed search on 9 October 2026 for the exact phrase PEG-MGF returned one record, a 2026 narrative review, and there is no primary study of the pegylated peptide in any species. No controlled human study exists, and a 2010 review states that no free-standing MGF peptide has been isolated from cells, tissues or fluids.

Pegylated mechano growth factor (C-terminal peptide of the IGF-IEb splice variant)

  • MGF is the name given to the IGF-IEb mRNA splice variant, upregulated in skeletal muscle after injury and mechanical loading; the synthetic peptide people inject corresponds to its 24 most C-terminal residues.
  • A 2010 review states that no analogous peptide product of the Igf1 gene has been identified in or isolated from cultured cells, their conditioned medium, or animal tissues or biological fluids.
  • In healthy men aged 74, 5 weeks of resistance training increased MGF mRNA in vastus lateralis biopsies by 163%; nobody in that study received MGF.
  • In cultured myoblasts, the MGF E domain peptide inhibited terminal differentiation while increasing proliferation, through a receptor that has not been identified.
  • A synthetic MGF E peptide stimulated prostate cancer cell growth, and silencing the IGF-1 receptor or insulin receptor did not affect that activity.
  • A PubMed search on 9 October 2026 for the exact phrase PEG-MGF returned 1 record, and a search for mechano growth factor with nitrogen balance or nitrogen retention returned 0 records.

What are MGF and PEG-MGF, and are they approved for anything?

The name MGF covers a gene splice variant and a synthetic 24-residue peptide, and PEG-MGF is the pegylated form of that peptide that is sold. No approval for MGF or PEG-MGF appears in the records reviewed, and a PubMed search for the exact phrase PEG-MGF returned one record, a review.

The gene variant. MGF is the name given to the IGF-IEb mRNA splice variant, which is upregulated in skeletal muscle after injury and mechanical loading, with upregulation correlating with markers of satellite cell and myoblast proliferation. The splice variant is well documented.

The unpegylated peptide. A synthetically manufactured peptide, also termed MGF, corresponds to the 24 most C-terminal residues of IGF-IEb and has been shown to promote cellular proliferation and survival in cell work.

PEG-MGF. This is the pegylated form of that synthetic peptide, and it is the product sold. No formula or molecular weight is printed, because pegylation specifications differ by manufacturer and no reference product exists. All the biology on this page belongs to the gene variant or to the unpegylated peptide, not to PEG-MGF.

A PubMed search on 9 October 2026 for the exact phrase PEG-MGF returned 1 record, a 2026 narrative review. A ClinicalTrials.gov query for mechano growth factor returned 8 studies, none of an MGF or PEG-MGF product; they cover acromegaly, multiple sclerosis, growth hormone in Phelan McDermid syndrome, robatumumab, maternal environmental enteric dysfunction, retinopathy of prematurity, IGF-I in hyperinsulinism and hydrocortisone in Addison disease. No approval for MGF or PEG-MGF appears in the records reviewed, and the 2026 review notes the absence of regulatory approval for physique or performance indications.

2010 endocrinology review: splice variant documented, free peptide never isolated

Narrative review

Matheny RW Jr et al. Endocrinology. 2010;151(3):865-75. PMID 20130113.

MGF is the name given to the IGF-IEb mRNA splice variant, which is upregulated in skeletal muscle after injury and mechanical loading, with upregulation correlating with markers of satellite cell and myoblast proliferation. A synthetically manufactured peptide, also termed MGF, corresponding to the 24 most C-terminal residues of IGF-IEb, has been shown to promote cellular proliferation and survival. However, as the review states, 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.

Participants / model
Review of cell, animal and human gene expression work
Treatment
Not applicable; synthetic peptide versus gene product
Follow-up
Not applicable
Study design
Review in a primary endocrinology journal
Funding
not stated in the source

The gene splice variant is well documented. The free-standing peptide people inject has not been shown to exist in the body.

Read the original source
Searches, 9 October 2026: one record for PEG-MGF, a review; no primary study

PubMed search record

PubMed search run on 9 October 2026: the exact phrase PEG-MGF, 1 record. A broader PubMed search for PEG-MGF or pegylated mechano growth factor, 5 records. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention, 0 records. A ClinicalTrials.gov query for mechano growth factor, 8 studies.

A PubMed search for the exact phrase PEG-MGF returned 1 record, the 2026 narrative review. A broader search for PEG-MGF or pegylated mechano growth factor returned 5 records; the other 4 concern PEGylated IGF-I conjugates, a first-in-man PEGylated recombinant human IGF-I study, PEG-rhGH dosing and an IGF-I system review, none of which is PEG-MGF. A ClinicalTrials.gov query for mechano growth factor returned 8 studies, none of an MGF or PEG-MGF product; they cover acromegaly, multiple sclerosis, growth hormone in Phelan McDermid syndrome, robatumumab, maternal environmental enteric dysfunction, retinopathy of prematurity, IGF-I in hyperinsulinism and hydrocortisone in Addison disease. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention returned 0 records. The records reviewed contain no primary study of PEG-MGF of any kind, in any species, and no study of nitrogen balance for MGF or PEG-MGF.

Participants / model
Records returned, not a population
Treatment
Not applicable
Follow-up
Searches run on 9 October 2026
Study design
Literature and registry searches
Funding
not stated in the source

A search result shows what the databases returned on that date. It is not proof that no unindexed study exists.

Read the original source
2026 narrative review: PEG-MGF listed among IGF-1 analogues, evidence tiers, class-level adverse effects

Narrative review

Dominikowski A et al. Front Endocrinol (Lausanne). 2026;17:1822475. PMID 42395176.

A 2026 narrative review of performance-enhancing peptides modulating the GH-IGF-1 axis lists pegylated mechano growth factor (PEG-MGF) alongside IGF-1 LR3 among the IGF-1 analogues encountered in clinical practice and online self-administration protocols. It stratifies peptides into evidence tiers running from regulatory-grade randomized trial data down to a complete absence of human studies, notes the absence of regulatory approval for physique or performance indications and the uncertainty around product composition, dose and stacking practices in unregulated supply chains, and describes class-level reported adverse effects spanning endocrine and metabolic disturbances including prolactin and cortisol elevations and dysglycaemia, fluid retention syndromes, myalgia and arthralgia, and injection-site reactions. It also flags biologically plausible but unproven mitogenic concerns for the class.

Participants / model
Review of published evidence and reported self-administration practice
Treatment
Narrative review, no new exposure
Follow-up
Not applicable
Study design
Narrative review
Funding
not stated in the source

The adverse effects are class-level statements and are not data on PEG-MGF. This review is the only PubMed record for the exact phrase PEG-MGF.

Read the original source

Has the injected MGF peptide been found in the body?

No. A 2010 review states that no analogous peptide product of the Igf1 gene has been identified in or isolated from cultured cells, their conditioned medium, or animal tissues or biological fluids. The splice variant is documented, but the free-standing peptide has not been shown to exist in the body.

The gene splice variant is well documented. The free-standing peptide that people inject is a different matter. A 2010 review in an endocrinology journal states 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.

That matters for the sales premise that injecting the peptide restores a natural signal. The sources reviewed do not show that the natural signal exists in peptide form.

2010 endocrinology review: splice variant documented, free peptide never isolated

Narrative review

Matheny RW Jr et al. Endocrinology. 2010;151(3):865-75. PMID 20130113.

MGF is the name given to the IGF-IEb mRNA splice variant, which is upregulated in skeletal muscle after injury and mechanical loading, with upregulation correlating with markers of satellite cell and myoblast proliferation. A synthetically manufactured peptide, also termed MGF, corresponding to the 24 most C-terminal residues of IGF-IEb, has been shown to promote cellular proliferation and survival. However, as the review states, 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.

Participants / model
Review of cell, animal and human gene expression work
Treatment
Not applicable; synthetic peptide versus gene product
Follow-up
Not applicable
Study design
Review in a primary endocrinology journal
Funding
not stated in the source

The gene splice variant is well documented. The free-standing peptide people inject has not been shown to exist in the body.

Read the original source

What do cell studies show for the unpegylated peptide?

In cultured myoblasts the MGF E domain peptide inhibited terminal differentiation while increasing proliferation, through a receptor that has not been identified. There is no primary study of PEG-MGF in any species.

The founding cell experiment for the muscle claim used cultured myoblasts and the unpegylated E domain peptide. Unlike mature IGF-I, the distinct E domain of MGF inhibited terminal differentiation while increasing myoblast proliferation. Blocking the IGF-I receptor with a specific antibody indicated that the function of the MGF E domain is mediated via a different receptor, which has not been identified. The paper carries a published erratum (FEBS Lett 2006;580(10):2530), which should be read before the result is cited.

A review of the E domain literature describes a synthetic analogue corresponding to the last 24 amino acids of the E domain of the IGF-1Ec isoform, used to elucidate its potential biological role, and notes that IGF-1Ec expression is upregulated after injury in skeletal muscle, during post-infarctal myocardium remodelling, and in cancer tissues and cell lines. The review frames this as a putative bioactivity under investigation, not an established one.

These are cell results for the unpegylated peptide. A PubMed search on 9 October 2026 for the exact phrase PEG-MGF returned 1 record, a narrative review, and the records reviewed contain no primary study of PEG-MGF of any kind, in any species.

Cultured myoblasts: E domain peptide, proliferation up, differentiation blocked, receptor unidentified

Cell study

Yang SY et al. FEBS Lett. 2002;522(1-3):156-60. PMID 12095637.

Unlike mature IGF-I, the distinct E domain of MGF inhibited terminal differentiation while increasing myoblast proliferation. Blocking the IGF-I receptor with a specific antibody indicated the function of the MGF E domain is mediated via a different receptor, which has not been identified.

Participants / model
Cultured myoblasts
Treatment
Media exposure to the MGF E domain peptide
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a cultured myoblast result for the unpegylated E domain peptide. The paper carries a published erratum (FEBS Lett 2006;580(10):2530) that should be read before the result is cited.

Read the original source
E domain review: putative bioactivity under investigation, not established

Narrative review

Vassilakos G et al. Hormones (Athens). 2014;13(2):182-96. PMID 24776619.

A synthetic analogue corresponding to the last 24 amino acids of the E domain of the IGF-1Ec isoform has been used to elucidate its potential biological role. IGF-1Ec expression is upregulated after injury in skeletal muscle, during post-infarctal myocardium remodelling, and in cancer tissues and cell lines.

Participants / model
Review of cell and tissue work
Treatment
Synthetic 24-residue E domain analogue
Follow-up
Not applicable
Study design
Review
Funding
not stated in the source

The review frames the bioactivity as putative and under investigation, not established.

Read the original source
Searches, 9 October 2026: one record for PEG-MGF, a review; no primary study

PubMed search record

PubMed search run on 9 October 2026: the exact phrase PEG-MGF, 1 record. A broader PubMed search for PEG-MGF or pegylated mechano growth factor, 5 records. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention, 0 records. A ClinicalTrials.gov query for mechano growth factor, 8 studies.

A PubMed search for the exact phrase PEG-MGF returned 1 record, the 2026 narrative review. A broader search for PEG-MGF or pegylated mechano growth factor returned 5 records; the other 4 concern PEGylated IGF-I conjugates, a first-in-man PEGylated recombinant human IGF-I study, PEG-rhGH dosing and an IGF-I system review, none of which is PEG-MGF. A ClinicalTrials.gov query for mechano growth factor returned 8 studies, none of an MGF or PEG-MGF product; they cover acromegaly, multiple sclerosis, growth hormone in Phelan McDermid syndrome, robatumumab, maternal environmental enteric dysfunction, retinopathy of prematurity, IGF-I in hyperinsulinism and hydrocortisone in Addison disease. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention returned 0 records. The records reviewed contain no primary study of PEG-MGF of any kind, in any species, and no study of nitrogen balance for MGF or PEG-MGF.

Participants / model
Records returned, not a population
Treatment
Not applicable
Follow-up
Searches run on 9 October 2026
Study design
Literature and registry searches
Funding
not stated in the source

A search result shows what the databases returned on that date. It is not proof that no unindexed study exists.

Read the original source

What happens to MGF in muscle after lifting?

In healthy men aged 74, 5 weeks of resistance training raised MGF mRNA in muscle biopsies by 163%. Nobody in the study received MGF; it measures the body's own gene expression.

The human data that exist are about expression, not administration. In healthy men aged 74 plus or minus 1 year assigned to resistance training with placebo, resistance training with growth hormone, or growth hormone alone, vastus lateralis biopsies were taken at baseline, 5 weeks and 12 weeks.

Growth hormone alone did not change MGF mRNA at 5 weeks but increased IGF-IEa mRNA by 237%, and at 12 weeks MGF mRNA was up 80% from baseline. Five weeks of resistance training increased MGF mRNA by 163%, IGF-IEa by 68% and IGF-IEb by 75%, with no further change at 12 weeks. Five weeks of training combined with growth hormone increased MGF mRNA by 456% and IGF-IEa by 167%.

Nobody in this study received MGF. It measures the body's own gene expression in response to lifting and to growth hormone.

Healthy men aged 74: resistance training raised MGF mRNA by 163% at 5 weeks, no MGF given

Human study

Hameed M et al. J Physiol. 2004;555(Pt 1):231-40. PMID 14565994.

In healthy men aged 74 plus or minus 1 year assigned to resistance training with placebo, resistance training with growth hormone, or growth hormone alone, vastus lateralis biopsies were taken at baseline, 5 weeks and 12 weeks. Growth hormone alone did not change MGF mRNA at 5 weeks but increased IGF-IEa mRNA by 237%; at 12 weeks MGF mRNA was up 80% from baseline. Five weeks of resistance training increased MGF mRNA by 163%, IGF-IEa by 68% and IGF-IEb by 75%, with no further change at 12 weeks. Five weeks of training combined with growth hormone increased MGF mRNA by 456% and IGF-IEa by 167%.

Participants / model
Healthy elderly men, mean age 74
Treatment
Resistance training with or without growth hormone administration; muscle biopsy
Follow-up
12 weeks
Study design
Original clinical study
Funding
not stated in the source

Nobody in this study received MGF. It measures the body's own gene expression in response to lifting and to growth hormone.

Read the original source

Does PEG-MGF repair or build muscle, or improve nitrogen balance?

No study shows it. The satellite cell and myoblast claim is supported only in cultured cells for the unpegylated peptide, the muscle repair and growth claim has no in vivo study for PEG-MGF, and a search for MGF with nitrogen balance or retention returned 0 records.

Sellers describe pegylated mechano growth factor for muscle repair and growth after training or injury, through satellite cells, myoblasts and nitrogen balance.

The satellite cell and myoblast mechanism is supported only in cultured cells, for the non-pegylated E domain peptide. The muscle repair and growth claim has no in vivo study for PEG-MGF. The nitrogen balance claim has zero records in the literature searched: a PubMed search on 9 October 2026 for mechano growth factor with nitrogen balance or nitrogen retention returned 0 records.

The clinical literature lists the product among self-administration compounds. A 2026 narrative review lists PEG-MGF alongside IGF-1 LR3 among IGF-1 analogues encountered in clinical practice and online self-administration protocols. It stratifies peptides into evidence tiers running from regulatory-grade randomized trial data down to a complete absence of human studies, and notes the absence of regulatory approval for physique or performance indications and the uncertainty around product composition, dose and stacking practices in unregulated supply chains.

A broader PubMed search for PEG-MGF or pegylated mechano growth factor returned 5 records. The other 4 concern PEGylated IGF-I conjugates, a first-in-man PEGylated recombinant human IGF-I study, PEG-rhGH dosing and an IGF-I system review, and none is PEG-MGF.

Cultured myoblasts: E domain peptide, proliferation up, differentiation blocked, receptor unidentified

Cell study

Yang SY et al. FEBS Lett. 2002;522(1-3):156-60. PMID 12095637.

Unlike mature IGF-I, the distinct E domain of MGF inhibited terminal differentiation while increasing myoblast proliferation. Blocking the IGF-I receptor with a specific antibody indicated the function of the MGF E domain is mediated via a different receptor, which has not been identified.

Participants / model
Cultured myoblasts
Treatment
Media exposure to the MGF E domain peptide
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a cultured myoblast result for the unpegylated E domain peptide. The paper carries a published erratum (FEBS Lett 2006;580(10):2530) that should be read before the result is cited.

Read the original source
2026 narrative review: PEG-MGF listed among IGF-1 analogues, evidence tiers, class-level adverse effects

Narrative review

Dominikowski A et al. Front Endocrinol (Lausanne). 2026;17:1822475. PMID 42395176.

A 2026 narrative review of performance-enhancing peptides modulating the GH-IGF-1 axis lists pegylated mechano growth factor (PEG-MGF) alongside IGF-1 LR3 among the IGF-1 analogues encountered in clinical practice and online self-administration protocols. It stratifies peptides into evidence tiers running from regulatory-grade randomized trial data down to a complete absence of human studies, notes the absence of regulatory approval for physique or performance indications and the uncertainty around product composition, dose and stacking practices in unregulated supply chains, and describes class-level reported adverse effects spanning endocrine and metabolic disturbances including prolactin and cortisol elevations and dysglycaemia, fluid retention syndromes, myalgia and arthralgia, and injection-site reactions. It also flags biologically plausible but unproven mitogenic concerns for the class.

Participants / model
Review of published evidence and reported self-administration practice
Treatment
Narrative review, no new exposure
Follow-up
Not applicable
Study design
Narrative review
Funding
not stated in the source

The adverse effects are class-level statements and are not data on PEG-MGF. This review is the only PubMed record for the exact phrase PEG-MGF.

Read the original source
Searches, 9 October 2026: one record for PEG-MGF, a review; no primary study

PubMed search record

PubMed search run on 9 October 2026: the exact phrase PEG-MGF, 1 record. A broader PubMed search for PEG-MGF or pegylated mechano growth factor, 5 records. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention, 0 records. A ClinicalTrials.gov query for mechano growth factor, 8 studies.

A PubMed search for the exact phrase PEG-MGF returned 1 record, the 2026 narrative review. A broader search for PEG-MGF or pegylated mechano growth factor returned 5 records; the other 4 concern PEGylated IGF-I conjugates, a first-in-man PEGylated recombinant human IGF-I study, PEG-rhGH dosing and an IGF-I system review, none of which is PEG-MGF. A ClinicalTrials.gov query for mechano growth factor returned 8 studies, none of an MGF or PEG-MGF product; they cover acromegaly, multiple sclerosis, growth hormone in Phelan McDermid syndrome, robatumumab, maternal environmental enteric dysfunction, retinopathy of prematurity, IGF-I in hyperinsulinism and hydrocortisone in Addison disease. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention returned 0 records. The records reviewed contain no primary study of PEG-MGF of any kind, in any species, and no study of nitrogen balance for MGF or PEG-MGF.

Participants / model
Records returned, not a population
Treatment
Not applicable
Follow-up
Searches run on 9 October 2026
Study design
Literature and registry searches
Funding
not stated in the source

A search result shows what the databases returned on that date. It is not proof that no unindexed study exists.

Read the original source

How does MGF signal, and through which receptor?

As a gene variant, MGF is upregulated in loaded and injured muscle and tracks satellite cell and myoblast proliferation markers. For the E peptide, the receptor is unidentified in every source reviewed, and blocking or silencing the IGF-1 receptor did not account for its activity in two cell experiments.

As a gene variant, MGF is upregulated in skeletal muscle after injury and mechanical loading, with upregulation correlating with markers of satellite cell and myoblast proliferation.

For the synthetic E peptide, the receptor is not known. In cultured myoblasts, blocking the IGF-I receptor with a specific antibody indicated that the E domain acts through a different receptor, and in prostate cancer cells, silencing the IGF-1 receptor or insulin receptor did not affect the peptide's mitogenic activity. The page does not describe an IGF-1 receptor mechanism, because the sources reviewed do not support one.

No pharmacokinetic data exist for MGF or PEG-MGF in any species, so no half-life is given.

2010 endocrinology review: splice variant documented, free peptide never isolated

Narrative review

Matheny RW Jr et al. Endocrinology. 2010;151(3):865-75. PMID 20130113.

MGF is the name given to the IGF-IEb mRNA splice variant, which is upregulated in skeletal muscle after injury and mechanical loading, with upregulation correlating with markers of satellite cell and myoblast proliferation. A synthetically manufactured peptide, also termed MGF, corresponding to the 24 most C-terminal residues of IGF-IEb, has been shown to promote cellular proliferation and survival. However, as the review states, 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.

Participants / model
Review of cell, animal and human gene expression work
Treatment
Not applicable; synthetic peptide versus gene product
Follow-up
Not applicable
Study design
Review in a primary endocrinology journal
Funding
not stated in the source

The gene splice variant is well documented. The free-standing peptide people inject has not been shown to exist in the body.

Read the original source
Cultured myoblasts: E domain peptide, proliferation up, differentiation blocked, receptor unidentified

Cell study

Yang SY et al. FEBS Lett. 2002;522(1-3):156-60. PMID 12095637.

Unlike mature IGF-I, the distinct E domain of MGF inhibited terminal differentiation while increasing myoblast proliferation. Blocking the IGF-I receptor with a specific antibody indicated the function of the MGF E domain is mediated via a different receptor, which has not been identified.

Participants / model
Cultured myoblasts
Treatment
Media exposure to the MGF E domain peptide
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a cultured myoblast result for the unpegylated E domain peptide. The paper carries a published erratum (FEBS Lett 2006;580(10):2530) that should be read before the result is cited.

Read the original source
Prostate cancer tissue and cell lines: MGF overexpressed, E peptide stimulated growth

Cell study

Armakolas A et al. Prostate. 2010;70(11):1233-42. PMID 20564425.

MGF was overexpressed in human prostate cancer tissues and in PC-3 and LNCaP cells, remarkably higher in prostate cancer and prostatic intraepithelial neoplasia than in normal prostate tissue, while normal prostate epithelial cells did not express MGF at all. Exogenous administration of a synthetic MGF E peptide stimulated prostate cancer cell growth and activated ERK1/2 phosphorylation, and silencing the IGF-1 receptor or insulin receptor did not affect that mitogenic activity.

Participants / model
Human prostate tissue samples; HPrEC, PC-3 and LNCaP cell lines
Treatment
Exogenous synthetic MGF E peptide in culture
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a safety-relevant finding that follows from the mechanism. A growth signal that works independently of the IGF-1 and insulin receptors has an unknown receptor, which makes it harder to reason about than IGF-1. It is a cell and tissue result, not a measured risk in a person.

Read the original source

What risks and unknowns do the sources describe?

No primary study of PEG-MGF exists, so there are no human or animal safety data for it. In prostate cancer cells a synthetic MGF E peptide stimulated growth through a receptor that was not the IGF-1 or insulin receptor, and the 2026 review flags unproven mitogenic concerns for the class.

No primary study of PEG-MGF of any kind, in any species, appears in the records reviewed, so no human or animal safety data exist for it.

MGF was overexpressed in human prostate cancer tissues and in PC-3 and LNCaP cells, remarkably higher in prostate cancer and prostatic intraepithelial neoplasia than in normal prostate tissue, while normal prostate epithelial cells did not express MGF at all. Exogenous synthetic MGF E peptide stimulated prostate cancer cell growth and activated ERK1/2 phosphorylation, and silencing the IGF-1 receptor or insulin receptor did not affect that mitogenic activity. A growth signal that works independently of the IGF-1 and insulin receptors has an unknown receptor, which makes it harder to reason about than IGF-1. This is a cell and tissue result, not a measured risk in a person.

The 2026 narrative review describes class-level reported adverse effects for GH-IGF-1 axis performance peptides: endocrine and metabolic disturbances including prolactin and cortisol elevations and dysglycaemia, fluid retention syndromes, myalgia and arthralgia, and injection-site reactions. It also flags biologically plausible but unproven mitogenic concerns for the class. These are class-level statements, not data on PEG-MGF, and the review notes uncertainty around product composition, dose and stacking practices in unregulated supply chains.

Searches, 9 October 2026: one record for PEG-MGF, a review; no primary study

PubMed search record

PubMed search run on 9 October 2026: the exact phrase PEG-MGF, 1 record. A broader PubMed search for PEG-MGF or pegylated mechano growth factor, 5 records. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention, 0 records. A ClinicalTrials.gov query for mechano growth factor, 8 studies.

A PubMed search for the exact phrase PEG-MGF returned 1 record, the 2026 narrative review. A broader search for PEG-MGF or pegylated mechano growth factor returned 5 records; the other 4 concern PEGylated IGF-I conjugates, a first-in-man PEGylated recombinant human IGF-I study, PEG-rhGH dosing and an IGF-I system review, none of which is PEG-MGF. A ClinicalTrials.gov query for mechano growth factor returned 8 studies, none of an MGF or PEG-MGF product; they cover acromegaly, multiple sclerosis, growth hormone in Phelan McDermid syndrome, robatumumab, maternal environmental enteric dysfunction, retinopathy of prematurity, IGF-I in hyperinsulinism and hydrocortisone in Addison disease. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention returned 0 records. The records reviewed contain no primary study of PEG-MGF of any kind, in any species, and no study of nitrogen balance for MGF or PEG-MGF.

Participants / model
Records returned, not a population
Treatment
Not applicable
Follow-up
Searches run on 9 October 2026
Study design
Literature and registry searches
Funding
not stated in the source

A search result shows what the databases returned on that date. It is not proof that no unindexed study exists.

Read the original source
Prostate cancer tissue and cell lines: MGF overexpressed, E peptide stimulated growth

Cell study

Armakolas A et al. Prostate. 2010;70(11):1233-42. PMID 20564425.

MGF was overexpressed in human prostate cancer tissues and in PC-3 and LNCaP cells, remarkably higher in prostate cancer and prostatic intraepithelial neoplasia than in normal prostate tissue, while normal prostate epithelial cells did not express MGF at all. Exogenous administration of a synthetic MGF E peptide stimulated prostate cancer cell growth and activated ERK1/2 phosphorylation, and silencing the IGF-1 receptor or insulin receptor did not affect that mitogenic activity.

Participants / model
Human prostate tissue samples; HPrEC, PC-3 and LNCaP cell lines
Treatment
Exogenous synthetic MGF E peptide in culture
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a safety-relevant finding that follows from the mechanism. A growth signal that works independently of the IGF-1 and insulin receptors has an unknown receptor, which makes it harder to reason about than IGF-1. It is a cell and tissue result, not a measured risk in a person.

Read the original source
2026 narrative review: PEG-MGF listed among IGF-1 analogues, evidence tiers, class-level adverse effects

Narrative review

Dominikowski A et al. Front Endocrinol (Lausanne). 2026;17:1822475. PMID 42395176.

A 2026 narrative review of performance-enhancing peptides modulating the GH-IGF-1 axis lists pegylated mechano growth factor (PEG-MGF) alongside IGF-1 LR3 among the IGF-1 analogues encountered in clinical practice and online self-administration protocols. It stratifies peptides into evidence tiers running from regulatory-grade randomized trial data down to a complete absence of human studies, notes the absence of regulatory approval for physique or performance indications and the uncertainty around product composition, dose and stacking practices in unregulated supply chains, and describes class-level reported adverse effects spanning endocrine and metabolic disturbances including prolactin and cortisol elevations and dysglycaemia, fluid retention syndromes, myalgia and arthralgia, and injection-site reactions. It also flags biologically plausible but unproven mitogenic concerns for the class.

Participants / model
Review of published evidence and reported self-administration practice
Treatment
Narrative review, no new exposure
Follow-up
Not applicable
Study design
Narrative review
Funding
not stated in the source

The adverse effects are class-level statements and are not data on PEG-MGF. This review is the only PubMed record for the exact phrase PEG-MGF.

Read the original source

Why does PEG-MGF sit in D tier?

The gap between what is sold and what exists is wide: the splice variant is real, but PEG-MGF has no primary study in any species, the injected peptide has not been isolated from the body, and its E peptide stimulated prostate cancer cell growth through an unidentified receptor.

The gene splice variant is real and its expression in human muscle rises with resistance training, by 163% at 5 weeks in elderly men. The synthetic 24-residue E domain peptide has cell data showing myoblast proliferation through an unidentified receptor. PEG-MGF, the product actually sold, has exactly one PubMed record for the exact phrase, a 2026 narrative review that lists it as a self-administration compound, and no primary study in any species.

On top of that absence, a 2010 review states that no peptide product matching synthetic MGF has been isolated from cells, conditioned medium, animal tissue or body fluids, so the premise that injecting it restores a natural signal is unsupported. The marketing is ahead of a molecule whose existence in the body has not been shown.

2010 endocrinology review: splice variant documented, free peptide never isolated

Narrative review

Matheny RW Jr et al. Endocrinology. 2010;151(3):865-75. PMID 20130113.

MGF is the name given to the IGF-IEb mRNA splice variant, which is upregulated in skeletal muscle after injury and mechanical loading, with upregulation correlating with markers of satellite cell and myoblast proliferation. A synthetically manufactured peptide, also termed MGF, corresponding to the 24 most C-terminal residues of IGF-IEb, has been shown to promote cellular proliferation and survival. However, as the review states, 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.

Participants / model
Review of cell, animal and human gene expression work
Treatment
Not applicable; synthetic peptide versus gene product
Follow-up
Not applicable
Study design
Review in a primary endocrinology journal
Funding
not stated in the source

The gene splice variant is well documented. The free-standing peptide people inject has not been shown to exist in the body.

Read the original source
Cultured myoblasts: E domain peptide, proliferation up, differentiation blocked, receptor unidentified

Cell study

Yang SY et al. FEBS Lett. 2002;522(1-3):156-60. PMID 12095637.

Unlike mature IGF-I, the distinct E domain of MGF inhibited terminal differentiation while increasing myoblast proliferation. Blocking the IGF-I receptor with a specific antibody indicated the function of the MGF E domain is mediated via a different receptor, which has not been identified.

Participants / model
Cultured myoblasts
Treatment
Media exposure to the MGF E domain peptide
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a cultured myoblast result for the unpegylated E domain peptide. The paper carries a published erratum (FEBS Lett 2006;580(10):2530) that should be read before the result is cited.

Read the original source
Healthy men aged 74: resistance training raised MGF mRNA by 163% at 5 weeks, no MGF given

Human study

Hameed M et al. J Physiol. 2004;555(Pt 1):231-40. PMID 14565994.

In healthy men aged 74 plus or minus 1 year assigned to resistance training with placebo, resistance training with growth hormone, or growth hormone alone, vastus lateralis biopsies were taken at baseline, 5 weeks and 12 weeks. Growth hormone alone did not change MGF mRNA at 5 weeks but increased IGF-IEa mRNA by 237%; at 12 weeks MGF mRNA was up 80% from baseline. Five weeks of resistance training increased MGF mRNA by 163%, IGF-IEa by 68% and IGF-IEb by 75%, with no further change at 12 weeks. Five weeks of training combined with growth hormone increased MGF mRNA by 456% and IGF-IEa by 167%.

Participants / model
Healthy elderly men, mean age 74
Treatment
Resistance training with or without growth hormone administration; muscle biopsy
Follow-up
12 weeks
Study design
Original clinical study
Funding
not stated in the source

Nobody in this study received MGF. It measures the body's own gene expression in response to lifting and to growth hormone.

Read the original source
Prostate cancer tissue and cell lines: MGF overexpressed, E peptide stimulated growth

Cell study

Armakolas A et al. Prostate. 2010;70(11):1233-42. PMID 20564425.

MGF was overexpressed in human prostate cancer tissues and in PC-3 and LNCaP cells, remarkably higher in prostate cancer and prostatic intraepithelial neoplasia than in normal prostate tissue, while normal prostate epithelial cells did not express MGF at all. Exogenous administration of a synthetic MGF E peptide stimulated prostate cancer cell growth and activated ERK1/2 phosphorylation, and silencing the IGF-1 receptor or insulin receptor did not affect that mitogenic activity.

Participants / model
Human prostate tissue samples; HPrEC, PC-3 and LNCaP cell lines
Treatment
Exogenous synthetic MGF E peptide in culture
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a safety-relevant finding that follows from the mechanism. A growth signal that works independently of the IGF-1 and insulin receptors has an unknown receptor, which makes it harder to reason about than IGF-1. It is a cell and tissue result, not a measured risk in a person.

Read the original source
2026 narrative review: PEG-MGF listed among IGF-1 analogues, evidence tiers, class-level adverse effects

Narrative review

Dominikowski A et al. Front Endocrinol (Lausanne). 2026;17:1822475. PMID 42395176.

A 2026 narrative review of performance-enhancing peptides modulating the GH-IGF-1 axis lists pegylated mechano growth factor (PEG-MGF) alongside IGF-1 LR3 among the IGF-1 analogues encountered in clinical practice and online self-administration protocols. It stratifies peptides into evidence tiers running from regulatory-grade randomized trial data down to a complete absence of human studies, notes the absence of regulatory approval for physique or performance indications and the uncertainty around product composition, dose and stacking practices in unregulated supply chains, and describes class-level reported adverse effects spanning endocrine and metabolic disturbances including prolactin and cortisol elevations and dysglycaemia, fluid retention syndromes, myalgia and arthralgia, and injection-site reactions. It also flags biologically plausible but unproven mitogenic concerns for the class.

Participants / model
Review of published evidence and reported self-administration practice
Treatment
Narrative review, no new exposure
Follow-up
Not applicable
Study design
Narrative review
Funding
not stated in the source

The adverse effects are class-level statements and are not data on PEG-MGF. This review is the only PubMed record for the exact phrase PEG-MGF.

Read the original source
Searches, 9 October 2026: one record for PEG-MGF, a review; no primary study

PubMed search record

PubMed search run on 9 October 2026: the exact phrase PEG-MGF, 1 record. A broader PubMed search for PEG-MGF or pegylated mechano growth factor, 5 records. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention, 0 records. A ClinicalTrials.gov query for mechano growth factor, 8 studies.

A PubMed search for the exact phrase PEG-MGF returned 1 record, the 2026 narrative review. A broader search for PEG-MGF or pegylated mechano growth factor returned 5 records; the other 4 concern PEGylated IGF-I conjugates, a first-in-man PEGylated recombinant human IGF-I study, PEG-rhGH dosing and an IGF-I system review, none of which is PEG-MGF. A ClinicalTrials.gov query for mechano growth factor returned 8 studies, none of an MGF or PEG-MGF product; they cover acromegaly, multiple sclerosis, growth hormone in Phelan McDermid syndrome, robatumumab, maternal environmental enteric dysfunction, retinopathy of prematurity, IGF-I in hyperinsulinism and hydrocortisone in Addison disease. A PubMed search for mechano growth factor with nitrogen balance or nitrogen retention returned 0 records. The records reviewed contain no primary study of PEG-MGF of any kind, in any species, and no study of nitrogen balance for MGF or PEG-MGF.

Participants / model
Records returned, not a population
Treatment
Not applicable
Follow-up
Searches run on 9 October 2026
Study design
Literature and registry searches
Funding
not stated in the source

A search result shows what the databases returned on that date. It is not proof that no unindexed study exists.

Read the original source

Studies and sources

2010 endocrinology review: splice variant documented, free peptide never isolated

Narrative review

Matheny RW Jr et al. Endocrinology. 2010;151(3):865-75. PMID 20130113.

MGF is the name given to the IGF-IEb mRNA splice variant, which is upregulated in skeletal muscle after injury and mechanical loading, with upregulation correlating with markers of satellite cell and myoblast proliferation. A synthetically manufactured peptide, also termed MGF, corresponding to the 24 most C-terminal residues of IGF-IEb, has been shown to promote cellular proliferation and survival. However, as the review states, 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.

Participants / model
Review of cell, animal and human gene expression work
Treatment
Not applicable; synthetic peptide versus gene product
Follow-up
Not applicable
Study design
Review in a primary endocrinology journal
Funding
not stated in the source

The gene splice variant is well documented. The free-standing peptide people inject has not been shown to exist in the body.

Read the original source
Cultured myoblasts: E domain peptide, proliferation up, differentiation blocked, receptor unidentified

Cell study

Yang SY et al. FEBS Lett. 2002;522(1-3):156-60. PMID 12095637.

Unlike mature IGF-I, the distinct E domain of MGF inhibited terminal differentiation while increasing myoblast proliferation. Blocking the IGF-I receptor with a specific antibody indicated the function of the MGF E domain is mediated via a different receptor, which has not been identified.

Participants / model
Cultured myoblasts
Treatment
Media exposure to the MGF E domain peptide
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a cultured myoblast result for the unpegylated E domain peptide. The paper carries a published erratum (FEBS Lett 2006;580(10):2530) that should be read before the result is cited.

Read the original source
E domain review: putative bioactivity under investigation, not established

Narrative review

Vassilakos G et al. Hormones (Athens). 2014;13(2):182-96. PMID 24776619.

A synthetic analogue corresponding to the last 24 amino acids of the E domain of the IGF-1Ec isoform has been used to elucidate its potential biological role. IGF-1Ec expression is upregulated after injury in skeletal muscle, during post-infarctal myocardium remodelling, and in cancer tissues and cell lines.

Participants / model
Review of cell and tissue work
Treatment
Synthetic 24-residue E domain analogue
Follow-up
Not applicable
Study design
Review
Funding
not stated in the source

The review frames the bioactivity as putative and under investigation, not established.

Read the original source
Prostate cancer tissue and cell lines: MGF overexpressed, E peptide stimulated growth

Cell study

Armakolas A et al. Prostate. 2010;70(11):1233-42. PMID 20564425.

MGF was overexpressed in human prostate cancer tissues and in PC-3 and LNCaP cells, remarkably higher in prostate cancer and prostatic intraepithelial neoplasia than in normal prostate tissue, while normal prostate epithelial cells did not express MGF at all. Exogenous administration of a synthetic MGF E peptide stimulated prostate cancer cell growth and activated ERK1/2 phosphorylation, and silencing the IGF-1 receptor or insulin receptor did not affect that mitogenic activity.

Participants / model
Human prostate tissue samples; HPrEC, PC-3 and LNCaP cell lines
Treatment
Exogenous synthetic MGF E peptide in culture
Follow-up
not stated in the source
Study design
Original preclinical study
Funding
not stated in the source

This is a safety-relevant finding that follows from the mechanism. A growth signal that works independently of the IGF-1 and insulin receptors has an unknown receptor, which makes it harder to reason about than IGF-1. It is a cell and tissue result, not a measured risk in a person.

Read the original source
Healthy men aged 74: resistance training raised MGF mRNA by 163% at 5 weeks, no MGF given

Human study

Hameed M et al. J Physiol. 2004;555(Pt 1):231-40. PMID 14565994.

In healthy men aged 74 plus or minus 1 year assigned to resistance training with placebo, resistance training with growth hormone, or growth hormone alone, vastus lateralis biopsies were taken at baseline, 5 weeks and 12 weeks. Growth hormone alone did not change MGF mRNA at 5 weeks but increased IGF-IEa mRNA by 237%; at 12 weeks MGF mRNA was up 80% from baseline. Five weeks of resistance training increased MGF mRNA by 163%, IGF-IEa by 68% and IGF-IEb by 75%, with no further change at 12 weeks. Five weeks of training combined with growth hormone increased MGF mRNA by 456% and IGF-IEa by 167%.

Participants / model
Healthy elderly men, mean age 74
Treatment
Resistance training with or without growth hormone administration; muscle biopsy
Follow-up
12 weeks
Study design
Original clinical study
Funding
not stated in the source

Nobody in this study received MGF. It measures the body's own gene expression in response to lifting and to growth hormone.

Read the original source
2026 narrative review: PEG-MGF listed among IGF-1 analogues, evidence tiers, class-level adverse effects

Narrative review

Dominikowski A et al. Front Endocrinol (Lausanne). 2026;17:1822475. PMID 42395176.

A 2026 narrative review of performance-enhancing peptides modulating the GH-IGF-1 axis lists pegylated mechano growth factor (PEG-MGF) alongside IGF-1 LR3 among the IGF-1 analogues encountered in clinical practice and online self-administration protocols. It stratifies peptides into evidence tiers running from regulatory-grade randomized trial data down to a complete absence of human studies, notes the absence of regulatory approval for physique or performance indications and the uncertainty around product composition, dose and stacking practices in unregulated supply chains, and describes class-level reported adverse effects spanning endocrine and metabolic disturbances including prolactin and cortisol elevations and dysglycaemia, fluid retention syndromes, myalgia and arthralgia, and injection-site reactions. It also flags biologically plausible but unproven mitogenic concerns for the class.

Participants / model
Review of published evidence and reported self-administration practice
Treatment
Narrative review, no new exposure
Follow-up
Not applicable
Study design
Narrative review
Funding
not stated in the source

The adverse effects are class-level statements and are not data on PEG-MGF. This review is the only PubMed record for the exact phrase PEG-MGF.

Read the original source

Why is PEG-MGF in D tier?

D fits a product whose marketing is well ahead of its record. The splice variant is real and rises in human muscle with lifting, the unpegylated peptide has cell data through an unidentified receptor, and PEG-MGF, the product sold, has no primary study in any species. A 2010 review states that the injected peptide has not been isolated from cells, tissues or fluids, so the premise that it restores a natural signal is unsupported.