PEG-MGF vs IGF-1 LR3
Two IGF-1 family compounds sold for muscle. Neither has a human trial. What is the difference, and does the classic alternating protocol make sense?
Reviewed by the amino101 editorial team. , first published .
PEG-MGF and IGF-1 LR3 are the two IGF-1 family peptides that circulate in muscle building protocols, and the first thing to say is that neither has been given to a person in a trial. PEG-MGF is a pegylated copy of the E domain of mechano growth factor, the IGF-1 splice variant that muscle fibers make for a short period after loading. In cell culture the E peptide makes myoblasts proliferate; in mice, delivering the MGF gene grows muscle. The pegylated version sold online has no published pharmacokinetics in any species, and the days long half-life vendors quote is a claim, not a measurement. IGF-1 LR3 is a modified IGF-1 with 83 amino acids, engineered to resist the binding proteins that normally hold IGF-1 in reserve, which gives it a 20 to 30 hour half-life and two to three times the potency of native IGF-1. It was built as a cell culture reagent and is still one. Its main practical risk is hypoglycemia, because it acts like a weak, long lasting insulin. Both are prohibited by WADA under S2. PEG-MGF was placed in FDA Category 2 in 2023 and was reported as staying restricted after the February 2026 announcement. This is an educational comparison; the use people want from either compound is supported by rodents and cell dishes, not by human data.
| PEG-MGF | IGF-1 LR3 | |
|---|---|---|
| Typical dosage | 200 to 400 mcg | 20 to 50 mcg |
| Frequency | 2 to 3 times weekly on training days | once daily |
| Route | Subcutaneous, Intramuscular | Subcutaneous, Intramuscular |
| Half-life | minutes for the bare E peptide; claimed 2 to 3 days for the pegylated form without any published measurement | 20 to 30 hours, because it is not captured by IGF binding proteins |
| Cycle | 4 to 6 weeks | 4 to 6 weeks |
| Research level | Preclinical only | Preclinical only |
| Human trials | None | None |
| Status | Investigational, not approved anywhere, with no human trials. Prohibited by WADA under S2. | Research reagent, not FDA approved; banned in sport |
| Effects timeline | nothing to feel; any change in recovery or muscle is judged over 4 to 6 weeks and cannot be separated from training | muscle fullness and pumps 1 to 2 weeks, recovery 2 to 4 weeks, any size change only over the full cycle with training and food |
Key differences
PEG-MGF vs IGF-1 LR3 dosage
Dosage patterns reported in research and community protocols, by goal. Taken from each compound page. Not a prescription.
| Goal | Dosage | Frequency |
|---|---|---|
| Standard post-training protocol, community | 200 mcg | 3 times weekly after training |
| Higher end | 400 mcg | 2 times weekly after the hardest sessions |
| Bilateral split, community | 200 mcg per side | 2 times weekly after training |
| Alternating with IGF-1 LR3 | 200 to 300 mcg | 2 to 3 times weekly, on weeks without IGF-1 LR3 |
| Goal | Dosage | Frequency |
|---|---|---|
| First cycle | 20 mcg | once daily after training, with food |
| Standard | 40 mcg | once daily after training, with food |
| Upper end | 50 mcg | once daily, only if lower doses were tolerated |
| Training days only | 40 mcg | after each session, skipping rest days |
Convert any of these to syringe units in the dosage calculator.
Side effects compared
- ▲Injection site soreness, bruising or swelling, more so with intramuscular injection
- ▲Transient lightheadedness after a dose
- ▲Mild hypoglycemia symptoms have been reported anecdotally, unverified
- ▲Joint aches when stacked with IGF-1 LR3 or secretagogues
- ▲Infection or nerve irritation from repeated intramuscular injections
- ▲Hypoglycemia with shakiness, sweating, hunger, and brain fog
- ▲Headache
- ▲Water retention
- ▲Joint aches
- ▲Injection site pain or bruising
Which should you choose?
PEG-MGF fits only someone who has read the compound page, understands that there is no human or even animal data on the pegylated peptide, and wants to run it anyway as an experiment. Community protocols report 200 to 400 mcg, 2 to 3 times weekly within an hour or two of training, for 4 to 6 weeks. Subcutaneous injection is the sane route; injecting into trained muscle adds infection and nerve risk with no demonstrated local effect.
IGF-1 LR3 fits an experienced user whose goal is muscle specifically, who will start at 20 mcg, inject after training with a carbohydrate meal, never dose fasted or before bed, and keep glucose tablets nearby for the first several doses. Most people find nothing above 50 mcg except side effects. It is not a fat loss compound, not a recovery compound, and not a first peptide. It is also sold as a cell culture reagent, which is what it is.
Neither, for most people. Both are IGF-1 family compounds that push cells to grow, both carry the same theoretical cancer concern, and both lack a single human study for the purpose they are sold for. If one of them has to be chosen, IGF-1 LR3 at least has measured pharmacology, a known half-life and a known main risk, which means an experienced user can manage it by dosing low, injecting after training with carbohydrate and keeping fast sugar on hand. PEG-MGF is a vendor invention layered on a real but narrow piece of muscle biology, with no evidence that a circulating pegylated peptide does what a locally expressed splice variant does inside a fiber. The classic protocol that alternates PEG-MGF and LR3 to mimic the proliferation then differentiation sequence seen in rodent muscle is a tidy theory that nobody has tested. For the broader question of what either can do next to the compounds people actually compare them with, see IGF-1 LR3 vs HGH and peptides vs steroids. Both are prohibited in sport and this page is educational, not a plan.
Stacking: The classic community pairing: PEG-MGF after training to expand satellite cells, IGF-1 LR3 on other days or in alternating weeks to drive growth. It mirrors the rodent splicing sequence and has never been tested in anyone.
PEG-MGF is a pegylated copy of the E domain peptide of mechano growth factor, the IGF-1 splice variant muscle produces after loading or damage. In rodents and cell cultures it activates satellite cells and promotes repair. There are no human trials of any kind, and the pegylated version sold online has barely been studied even in animals.
IGF-1 LR3 is a modified, long-acting version of insulin-like growth factor 1 that resists binding proteins and stays active for most of a day. People use it for muscle growth and recovery, and it carries a real risk of low blood sugar.
PEG-MGF vs IGF-1 LR3: frequently asked
Does PEG-MGF build muscle?
In mice, delivering the MGF gene into muscle increased fiber size, and the E peptide expands myoblasts in culture. In people there is no evidence either way, because no trial has injected it into anyone. The body already makes MGF after every hard training session. Community reports are mixed and are confounded by the training, food and other compounds people run alongside it.
Is IGF-1 LR3 stronger than PEG-MGF?
They are not doing the same job, at least in theory. LR3 hits the IGF-1 receptor directly for most of a day and drives protein synthesis; the MGF E peptide is thought to act on a different receptor to make satellite cells multiply. In practice LR3 is the one with a measurable effect, hypoglycemia, and a measurable half-life. PEG-MGF has neither, so there is no way to say it is weaker, only that nothing about it has been measured.
Can you take PEG-MGF and IGF-1 LR3 together?
The common protocol alternates them rather than injecting both at once: PEG-MGF after training, LR3 on rest days or in separate weeks, on the theory that proliferation should come before differentiation. There is no study of the pair. Stacking two IGF family compounds compounds the cell growth concern, and anyone with a cancer history has a clear reason to skip both.
Does PEG-MGF cause low blood sugar like IGF-1 LR3?
LR3 reliably does, because it is structurally close enough to insulin to activate the insulin receptor and it stays active for 20 to 30 hours. PEG-MGF's effect on glucose is unknown; mild hypoglycemia symptoms have been reported anecdotally and never verified. Anyone combining either with insulin is in territory that community reports describe as dangerous.
Do you need to inject PEG-MGF or IGF-1 LR3 into the muscle you trained?
Not LR3. Its half-life is nearly a day and it circulates everywhere, so the injection site is folklore. PEG-MGF is injected into trained muscle by some people on the theory that MGF acts locally, but a pegylated peptide still diffuses into the bloodstream, and there is no evidence that local injection produces local growth. Intramuscular injection adds infection and nerve injury risk; the peptide injection sites article covers the safer options.
Are PEG-MGF and IGF-1 LR3 banned?
Both are prohibited by WADA under S2 as growth factors. In the US, PEG-MGF has been in FDA Category 2 since 2023 and reports on the February 2026 HHS announcement list it among the peptides expected to stay restricted. IGF-1 LR3 is not approved anywhere and is sold as a laboratory reagent. For what testing can detect, see do peptides show up on a drug test.
Related reading
Muscle growth and body composition
The messenger and the hormone. Why one is a cell culture reagent and the other is an approved drug.
Guide
Guide
Guide
Guide
Sources
- Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation. FEBS Letters, 2002
- Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise. Journal of Physiology, 2003
- Long R3 IGF-1: a potent IGF-1 analog with reduced binding protein affinity. Journal of Molecular Endocrinology, 1992
- Mecasermin (Increlex) prescribing information. US Food and Drug Administration, 2005