MGF

MGF (mechano growth factor), known as IGF-1Ec in humans, is a splice variant of insulin-like growth factor 1 (IGF-1). Alternative splicing lets a single gene produce several related proteins, and in this case the IGF1 gene yields a form with a distinctive C-terminal E-domain tail that the liver-made IGF-1Ea form lacks ¹. Muscle produces MGF rapidly after mechanical loading or injury, where it behaves as an early repair signal rather than a steady hormone ².

Two related products are studied. Full-length MGF (pro-IGF-1Ec) activates the classic IGF-1 receptor, about nine times less potently than IGF-1 itself ⁴. The short synthetic E-domain peptide (MGF-Ct24E, also called Goldspink-MGF) does not touch that receptor at all and works through a separate, still-unidentified pathway ³. Most of the tissue-repair literature, and most community use, involves this E-domain peptide.

Research spans skeletal muscle repair, tendon and ligament healing, cartilage protection in osteoarthritis, neuroprotection after ischemia, and cardiac recovery after heart attack, all in animal and cell models ¹⁰. No human trial of exogenous MGF exists ³³.

MGF's split personality comes from its two forms. The IGF1 gene has six exons, and alternative splicing produces three prohormones that all carry the same 70-amino-acid mature IGF-1 peptide but differ in their E-domain tails ². The Ec tail is what makes MGF different.

Two receptor profiles

Full-length MGF activates the IGF-1 receptor, reaching the same maximal activation as IGF-1 but with roughly ninefold lower potency (EC50 7.83 vs 0.86 nM), and it also stimulates insulin receptors IR-A and IR-B ⁴. The isolated E-domain peptide does not activate the IGF-1 receptor at any concentration ⁴. Instead it switches on ERK1/2 growth signaling without activating Akt, the opposite pattern of mature IGF-1. Blocking the IGF-1 receptor leaves E-domain effects intact, so a distinct receptor is involved, and it has not yet been identified ³.

The native repair signal

Muscle raises MGF transcript within hours of mechanical overload or damage, and the signal shifts toward IGF-1Ea during later remodeling. That timing places MGF as a quick-start trigger for repair ¹. The E-domain peptide reinforces that job: it attracts human mesenchymal stem cells more potently than mature IGF-1 after 20 hours ²⁸, and it blocks the cell-death program by preserving mitochondrial membrane potential and stopping caspase-3 activation, which reduced dying cells in post-heart-attack mouse hearts ¹². Downstream wiring varies by tissue: FAK-ERK1/2 in tendon cells ³⁵, PI3K-Akt plus MEK-ERK1/2 in cartilage cells under low oxygen ¹⁷, and Erk5-MEF2C in intestinal smooth muscle ²².

A gap in the picture

No human pharmacokinetic study exists, and the E-domain has never been isolated as a free peptide from tissues or biological fluids, so clearance is undefined ². Effective concentrations in cell work sit around 10 to 60 ng/mL ¹⁸. Community practice treats the native peptide as very short-lived and favors PEG-MGF, a pegylated version, for multi-hour activity, but this has not been formally measured.

Muscle

The E-domain peptide increases proliferation of myoblasts (muscle precursor cells) and delays their maturation into fibers ³. It also improved engraftment of transplanted human muscle precursor cells in mice ¹⁰ and raises the fusion potential of human muscle progenitor cells across ages ²⁷. A conflicting study found no effect of the C-terminal peptide on myoblasts or primary muscle stem cells, so this finding base is genuinely mixed ⁸. In injured mouse muscle, MGF overexpression also delayed macrophage clearance and sustained a pro-inflammatory state without changing final regeneration outcomes ⁹.

Human data are expression data, not treatment data. IGF-1Ec mRNA rises in thigh muscle after eccentric (lengthening) contractions but not concentric ones ⁶. Under medically induced testosterone suppression, the exercise-driven rise fell from 4.7-fold to 2-fold alongside blunted hypertrophy ⁵. And aged rats fail to upregulate MGF after overload, which correlates with poor satellite-cell activation ⁷.

Tendon, ligament, and cartilage

MGF restored migration and adhesion of mechanically injured human ACL fibroblasts and accelerated ACL regeneration in a rabbit partial-tear model ²⁰. In osteoarthritis models it boosted chondrocyte proliferation and matrix synthesis and slowed cartilage degeneration in rabbits ¹⁷. In a transgenic rat model of ankylosing spondylitis, MGF delayed arthritis onset from day 14 to day 23 and shifted inflammatory signaling toward resolution ¹⁹.

Nerves and heart

The E-domain peptide protected neurons in a gerbil model of transient brain ischemia, matching full-length IGF-1 potency with longer-lasting effect ¹⁴. Transgenic overexpression increased new neurons in the aging mouse brain and preserved olfactory function at 24 months ¹⁵, and the peptide protects sensory neurons from cisplatin toxicity via nucleolin binding ¹⁶. In the heart, MGF expression rises late after infarction ³², and E-domain delivery reduced apoptosis and preserved function in mouse heart-attack models ¹². Cardiac effects are dose-biphasic in mice, with low and high doses depressing contractility and a mid-dose doing the opposite ¹¹.

Where the evidence stands

No human trial has tested exogenous MGF for any of these endpoints ³³. Confidence in each indication tracks the animal and cell data above, and the muscle-repair claim remains the most contested.

Everything below traces back to community and practitioner protocols, because no human dose-finding study exists for MGF ³³. The anchor for those protocols is the endogenous signal: IGF-1Ec mRNA rises acutely after eccentric contractions ⁶ and after exercise-induced muscle damage ³⁹, so community protocols time injections to that window.

The timeline above shows a representative community schedule.

Form	Route	Dose	Frequency	Cycle
MGF E peptide, site-local	IM into trained muscles	50-200 mcg per muscle; 100-400 mcg per session	Post-workout on training days	4-6 weeks
PEG-MGF, systemic	SC or IM	200-500 mcg	2-3 times per week	4-8 weeks
Full-length MGF	IM or SC	100-300 mcg	Post-workout	4-6 weeks

Timing

Post-workout delivery follows the evidence that IGF-1Ec message rises quickly after eccentric loading and after muscle damage in humans ⁶. PEG-MGF carries a longer reported activity window, so community timing for it is less strict. Community scaling runs about 1.5 to 5 mcg per kilogram per muscle for MGF and 2.5 to 7 mcg per kilogram per dose for PEG-MGF.

Duration

Animal studies used windows of 2 weeks (mouse cardiac ¹¹, rabbit knee OA ¹⁸), 4 weeks (rabbit ACL ²⁰), and 6 to 7 weeks (rat OA and AS models ¹⁹). Community cycles run 4 to 8 weeks on followed by 4 or more weeks off; cycling reflects caution about sustained proliferative signaling, not documented desensitization.

Oral MGF has no absorption data and is considered ineffective; injection is the only route with any evidence (community practice).

MGF research products are lyophilized (freeze-dried) peptides, either full-length IGF-1Ec or the 24-amino-acid E-domain fragment, and they must be dissolved before use ²⁵. The standard diluent is bacteriostatic water (0.9% benzyl alcohol), which supports multi-dose vials; solutions made with plain sterile water should be used immediately (community practice).

Handle it gently. Let the sealed vial reach room temperature before opening to avoid condensation on the dry cake, drip diluent against the vial wall, and rotate rather than shake. The short E-domain peptide is aggregation-prone under agitation ²⁵.

Storage

• Unreconstituted powder: -20°C for 12 months or more; 2-8°C is fine for weeks to a few months. Protect from light and humidity (community practice).
• Reconstituted solution: refrigerate at 2-8°C and use within roughly 14 to 30 days; discard if cloudy or particulate. Do not refreeze. For longer storage, aliquot and freeze at -20°C for up to about 3 months, avoiding repeated freeze-thaw cycles (community practice).

Stability work supports the peptide's durability in protected carriers: sustained release from microrods still recruited stem cells after two weeks ⁴³, and microencapsulation was used specifically to preserve bioactivity ⁶⁰. The native non-amidated sequence is metabolically fragile, and stabilized C-terminally amidated analogues dominate black-market supply ²⁵.

The calculator below handles dilution math for your vial size, so you do not need to work out concentrations by hand.

No formal drug-interaction studies exist for MGF; the picture below extrapolates from pharmacology and from human studies of endogenous expression ³³.

• GH and GH secretagogues: synergistic. GH drives MGF expression in muscle cells ⁴⁶ and is the dominant stimulus in GH-deficient mouse muscle ³⁶. Stacks with ipamorelin or CJC-1295 add endocrine load, so glucose, cortisol, and prolactin monitoring appears in research guidance ³³.
• Androgens: synergistic. Testosterone induces MGF through an early transcriptional program ⁴⁸, and androgen suppression blunts exercise-induced IGF-1Ec upregulation in humans ⁵.
• Insulin and secretagogues: theoretical additive effect, full-length MGF only. It activates insulin receptors with high maximal efficacy but far weaker potency than insulin ⁴. The isolated E-peptide does not activate these receptors ⁴.
• Glucocorticoids: antagonistic. Dexamethasone suppresses MGF while inducing muscle atrophy in rats, and hydrogen sulfide donors restore MGF expression ⁴⁹.
• Cisplatin: protective in sensory neurons via nucleolin binding, research-stage only ¹⁶.
• IGF-1R blockers: neutral for the E-peptide, since its signaling survives IGF-1R blockade ³.
• MEK/ERK inhibitors: would blunt E-domain proliferative signaling, which runs through ERK1/2 rather than Akt ³.

Condition-level cautions include fibrostenotic Crohn's disease, where MGF drives smooth-muscle hypertrophy and stricture formation via Erk5 ²², and vascular disease, where MGF appears in neointima around stent struts and promotes smooth-muscle growth ⁵².

Cycling conversations around MGF rest on two ideas that matter more than receptor desensitization. First, MGF is a transient injury signal, not a tonic hormone: it rises acutely with overload and gives way to IGF-1Ea during remodeling ¹, and aged muscle loses this burst ⁷. Pulsed courses are meant to approximate that native pattern. Second, because the E-peptide is mitogenic in cancer cell models ²³, time-limited exposure caps cumulative proliferative signaling (community rationale).

Form	Dose	Frequency	Cycle
MGF E peptide	50-200 mcg per muscle; 100-400 mcg per session	2-4 times per week, post-workout	4-8 weeks on, 4 weeks off
PEG-MGF	200-400 mcg	2-3 times per week	8-12 weeks on, 4-8 weeks off

These are community patterns with no human validation ³³. The need to cycle is not driven by documented receptor tolerance, and it is worth remembering that one study found no effect of the C-terminal peptide on myoblasts at all ⁸, so the benefit itself is contested.

Signals that practitioners use to call for a break: a plateau in recovery effect, injection-site reactions or fluid retention ³³, dysglycemia symptoms ³³, and any persistent nodule or swelling given MGF's cancer-tissue associations ²³ (community observation).

Common combinations reported in the literature and in community practice, with what the evidence supports.

• IGF-1 LR3: complementary rather than redundant. The E-domain signals through ERK1/2 while mature IGF-1 signals through Akt and the IGF-1 receptor, and MGF plus IGF-1 were additive in a neuroprotection model ³. Full-length MGF is the redundant partner here, since it re-activates the same receptor at about ninefold lower potency ⁴.
• GH secretagogues (ipamorelin, CJC-1295, sermorelin): synergy through GH-driven MGF expression ³⁶; standard growth-axis stacks add endocrine and metabolic burden, so monitoring GH-axis labs and glucose follows ³³.
• BPC-157 and TB-500: a common healing stack with no conflict data. One nuance from the muscle-injury work: MGF delays macrophage resolution ⁹, worth keeping in mind when timing these around acute injury.
• TGF-beta3: synergy for cartilage in rabbit osteochondral scaffolds, with markedly better stem-cell recruitment and hyaline markers than either alone ⁵⁶.
• FGF-2: mixed. MGF plus FGF-2 outperformed MGF alone on postmitotic neurons, but the combination failed to reproduce FGF-2's apoptosis protection in neural stem-cell assays ⁵⁵.

Form selection matters in any stack: full-length and E-domain MGF differ in receptor pharmacology ⁴, and black-market vials have tested as amidated analogues rather than human-sequence peptide ²⁵.

MGF has no FDA approval for any indication, no EMA or other major-jurisdiction marketing authorization, and no documented clinical development program ²⁵. It is not a scheduled substance under the Controlled Substances Act, but it circulates as an unapproved research chemical in grey-market channels, outside any pharmaceutical quality system ³³.

Anti-doping status is strict. WADA prohibits mechano growth factors at all times, in and out of competition, under the S2 peptide hormones category, and the ban covers analogues including the amidated black-market variants ²⁵. Urine methods detect MGF-class peptides at limits of 5 to 50 pg/mL ²⁶, and a diagnostic transition (m/z 717.8 to 431.1) distinguishes the C-terminally amidated analogue from endogenous forms, so confirmed exogenous use is detectable ²⁵. Full-length biotechnologically produced MGF has been characterized specifically for doping-control purposes ⁵⁷.

For drug-tested athletes, mislabeled grey-market MGF carries strict-liability risk. Seized products have repeatedly tested as modified analogues rather than the human sequence ²⁵.

What is reported

No human safety trial exists for any form of MGF ³³. Class-level effects reported across growth-hormone and IGF-axis peptides include dysglycemia, fluid retention, muscle and joint pain, prolactin and cortisol changes, and injection-site reactions ³³. Community reports specific to MGF products add injection-site stinging and nodules, transient water retention, early-cycle lethargy and headache, and joint stiffness (community observation).

Mechanistic concerns

• Mitogenic risk: IGF-1Ec is overexpressed in prostate, colorectal, breast, and endometrial cancers, and the E-peptide drives growth of prostate cancer and osteosarcoma cells in culture ²³. An antibody against the E-domain reduced prostate tumor growth in mice ⁴¹. No human data show exogenous MGF causes cancer; the concern remains biologically plausible but unproven ³³.
• Cardiac: mouse work shows a non-linear dose response, with low and high doses depressing systolic and diastolic function and a mid-dose doing the opposite ¹¹.
• Inflammation: MGF overexpression in injured muscle delayed macrophage clearance and sustained pro-inflammatory signaling ⁹.
• Blood glucose: full-length MGF activates insulin receptors, creating a theoretical hypoglycemia risk at high doses; the isolated E-peptide does not ⁴.
• Stricture risk: in Crohn's disease tissue, MGF drives smooth-muscle hypertrophy and stricture formation ²².

Where caution is strongest

Absolute stops in the literature include active or prior malignancy, pregnancy and breastfeeding, recurrent hypoglycemia or type 1 diabetes with hypoglycemia unawareness, and known hypersensitivity. Relative cautions include structural heart disease, fibrostenotic Crohn's disease, diabetes or prediabetes, pediatric use (MGF is expressed in growth-plate cartilage with unknown exogenous effects) ³⁰, and elderly use given the age-related loss of the endogenous response ⁷. Product identity is a separate risk: seized vials have tested as amidated analogues ²⁵.

One open question deserves emphasis: whether the isolated E-domain peptide is bioactive in human muscle at all remains disputed, with one study reporting no effect on myoblasts or primary muscle stem cells ⁸, and no endogenous E-peptide has ever been isolated from tissues or fluids ².