IGF-1 LR3, IGF-1 DES and MGF: growth-factor peptides and the hypoglycemia problem

IGF-1: the hormone behind the peptides

Insulin-like growth factor 1 (IGF-1) carries out much of what growth hormone does: growth hormone signals the liver and other tissues to make IGF-1, and IGF-1 drives growth of bone, muscle and organs. As its name says, it is also structurally similar to insulin and shares many of insulin's effects. In a 1987 study in eight healthy adults, recombinant IGF-1 produced a fall in blood glucose nearly identical to insulin's at the doses used, reaching about 2 mmol/L after 30 minutes, although on a molecule-for-molecule basis it was only 6% as potent as insulin at lowering blood sugar ¹.

In the blood, IGF-1 is mostly locked up. More than 80% is bound in a complex with IGF-binding protein 3 and another protein, which controls how much is free to act and how fast it is cleared ². That restraint is the key to understanding the research peptides: two of them are designed or selected precisely because they escape it.

Three molecules sold under one idea

The peptides sold as 'IGF-1' for muscle are not IGF-1. From our encyclopedia entries, as of October 3, 2026:

IGF-1 LR3 Low is full-length IGF-1 with one amino acid swapped and a 13-amino-acid extension added at the start. It barely binds IGF-binding protein 3, so in cultured muscle cells that protein, which suppresses normal IGF-1, does not hold the analogue back in the same way ³. It was made as a reagent for growing cells and is still produced for that purpose ⁴.

IGF-1 DES Low, or des(1-3)IGF-1, is IGF-1 missing its first three amino acids. Unlike LR3, it occurs naturally in small amounts and has been isolated from bovine colostrum, human brain and pig uterus. Losing the glutamate at position 3 sharply reduces binding to IGF-binding proteins, which makes it about ten times as potent as IGF-1 at stimulating cultured cells; a 1996 review noted that its clinical use had not been evaluated ⁵.

MGF Low, mechano growth factor, is not an IGF-1 at all in the form sold. The IGF-1 gene can be read in several ways, and one variant, IGF-1Ec, rises in muscle after loading or injury; MGF products are a synthetic 24-amino-acid peptide from that variant's end piece ⁶. Our IGF-1 LR3 vs MGF comparison covers those two side by side.

What the research actually shows

None of the three has a published study in people. IGF-1 LR3's studies are in animals: infused for a week in guinea pigs it did not change body weight gain or carcass composition ⁷; injected in calves it lowered their own IGF-1 and growth hormone, and lowered blood glucose and insulin ⁸; in rats it increased intestinal glucose uptake ⁹; and in fetal sheep a short infusion lowered fetal insulin by 66% during a glucose clamp ¹⁰. IGF-1 DES's selective effects in animals were most evident in gut tissue ⁵. MGF's evidence is cultured human muscle cells, in which it extended the growth of satellite cells from young but not old donors ¹¹, and mice.

Not one of these studies tested muscle growth in healthy adult humans, which is what the products are sold for. The animal results that do exist point as much to effects on glucose and insulin as to growth.

The hypoglycemia problem

The clearest guide to what IGF-1 does in people comes from the one approved form. Mecasermin, sold as Increlex, is recombinant human IGF-1, approved for growth failure in children aged 2 and older with severe primary IGF-1 deficiency or growth hormone gene deletion with neutralising antibodies ². Its label's first warning is hypoglycaemia: severe low blood sugar leading to seizures has been observed, and because mecasermin has insulin-like effects it must be given within 20 minutes before or after a meal or snack, with glucose monitoring while the dose is adjusted ².

The numbers are striking. In clinical studies of 71 children treated for an average of 3.9 years, 30 (42%) had hypoglycaemia at least once; most episodes were mild or moderate, but five children had severe episodes needing help and four had seizures or loss of consciousness ². A later registry analysis found about 0.11 hypoglycaemia events per patient per treatment year, and identified factors predicting them ¹². That is in children with a genuine deficiency, under specialist supervision, using a product made to pharmaceutical standards with a known dose.

The research analogues raise the stakes. IGF-1 LR3 and IGF-1 DES are designed or selected to escape the binding proteins that normally buffer IGF-1, and both are more potent than IGF-1 in cells ^{5 3}. In calves, injected IGF-1 LR3 lowered blood glucose and insulin ⁸. Nobody has measured how much they lower blood sugar in people, how long the effect lasts, or how it interacts with exercise, fasting, alcohol or diabetes medicines. Low blood sugar can cause confusion, seizures and loss of consciousness, and it is most dangerous when it is not expected.

The cancer question

IGF-1 promotes cell growth and survival, which is why its link with cancer has been studied for decades. In UK Biobank, among 394,388 people without cancer at the start, higher blood IGF-1 was associated with higher risks of colorectal, breast, prostate and thyroid cancer, and with lower risks of ovarian and liver cancer, over about seven years; the authors noted that reverse causation could not be excluded ¹³. Those are associations within the normal range, not a measure of what a growth-factor injection does.

The approved drug's label is more direct. It reports postmarketing cases of malignant neoplasms in children treated with mecasermin, a variety of cancers, mostly in children with rare genetic conditions that already carry increased cancer risk, and says it is unknown whether the treatment is related; therapy should be stopped if cancer develops ². For MGF, tissue studies found its gene variant more highly expressed in colorectal cancers and high-grade polyps than in normal colon ¹⁴. None of this proves the research peptides cause cancer. It is why growth-factor peptides that escape the body's normal restraints are not a casual experiment.

Other risks on the approved label

Mecasermin's label lists further warnings that show what IGF-1 can do: severe allergic reactions including anaphylaxis, raised pressure inside the skull, enlarged tonsils and adenoids, slipped growth plates in the hip, worsening scoliosis, and, because of a benzyl alcohol preservative, a warning against use in infants ². Its trials also reported ear problems, headache and joint pain among common side effects ². These are effects of IGF-1 at controlled doses in children; adults injecting more potent analogues have no comparable safety information at all.

What is actually in the vial

Product quality is a separate problem. Researchers developing a doping test for IGF-1 analogues found oxidised, lower-quality peptide in black-market products ¹⁵. Anti-doping laboratories can now detect LongR3-IGF-1, R3-IGF-1 and DES(1-3)IGF-1 in plasma at low concentrations ¹⁶, reflecting long-standing interest in IGF-1 as an alternative to growth hormone among athletes, for whom IGF-1 compounds have been advertised online and on the black market for years ¹⁷. All of these are prohibited at all times under WADA's growth factors section ¹⁸.

Do they build muscle?

The honest answer is that nobody knows for these products, because nobody has tested them in people. IGF-1 mediates many of growth hormone's anabolic actions, which is why it attracts athletes ¹⁷, but the guinea pig study of IGF-1 LR3 found no change in carcass composition after a week ⁷, and the animal studies that report effects mostly concern the gut, glucose and insulin. Claims of rapid muscle growth come from forums and sellers, not studies, and they come attached to products of unknown purity.

The bottom line

As of October 3, 2026, IGF-1 LR3, IGF-1 DES and MGF are research reagents with animal and cell data and no published human studies. Two are more potent than the hormone whose only approved version causes low blood sugar in four in ten treated children and carries a seizure warning. Higher IGF-1 is associated with several cancers. If you are considering any of them, the questions are what is in the vial, what it will do to your blood sugar, and why you would take that risk on no human evidence. Nothing here is advice or a dose.

Frequently asked questions

What are the side effects of IGF-1 LR3?

No human study has measured them. IGF-1 lowers blood sugar like insulin, and the only approved IGF-1 caused hypoglycaemia in 42% of children in its trials, including seizures. IGF-1 LR3 is more potent in cells and escapes the body's normal restraints.

What is the difference between IGF-1 LR3 and IGF-1 DES?

LR3 is IGF-1 with a substitution and a 13-amino-acid extension; DES is IGF-1 missing its first three amino acids and occurs naturally in small amounts. Both bind IGF-binding proteins poorly, making them more potent than IGF-1 in cells.

Is MGF the same as IGF-1?

No. MGF products are a 24-amino-acid synthetic peptide from the IGF-1Ec splice variant, not the full IGF-1 hormone.

Is there an approved IGF-1?

Yes. Mecasermin (Increlex) is approved for children with severe primary IGF-1 deficiency, under specialist supervision, with warnings for hypoglycaemia, allergic reactions and other effects.

Related on Grey Peptides

• IGF-1 LR3
• Mecasermin
• IGF-1 LR3 vs MGF

Sources

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9. Garnaut, S. M., et al. (2002). Effects of insulin-like growth factor-I and its analogue, long-R3-IGF-I, on intestinal absorption of 3-O-methyl-D-glucose are less pronounced than gut mucosal growth responses. Growth Factors, 20(1), 17-25. PMID: 11999215
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18. Grey Peptides encyclopedia entries for IGF-1 LR3, IGF-1 DES, MGF and mecasermin: WADA 2026 and 2027 status S2.3. Read October 3, 2026.

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.