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What it is
IGF-1 LR3, also called Long R3 IGF-1, is a laboratory-made analog of insulin-like growth factor 1. It has an extended amino-terminal sequence and an arginine substitution at position 3. Those changes reduce its interaction with IGF-binding proteins, leaving more of the analog available to activate the IGF-1 receptor in experimental systems.
That design makes LR3 useful for studying growth signaling in cells, embryos, and animals. It does not make LR3 an approved form of prescription IGF-1. Published controlled human trials specific to LR3 are lacking, and a research vial should not be confused with mecasermin or another regulated medicine.
What people research it for
Growth-signaling research
Preclinical / theorizedLR3 is used to examine IGF-1 receptor signaling when binding-protein restraint is reduced. This is a laboratory use, not evidence of a human muscle-building treatment.
Cell culture growth and survival
Preclinical / theorizedCell-culture research uses LR3 as a growth factor for selected mammalian cells. Results in culture do not predict safety or whole-body effects in people.
Developmental biology
Animal studiesIn bovine embryo culture, LR3 changed cleavage, blastocyst cell counts, and expression of IGF-system genes. Native IGF-1 and LR3 affected different developmental measures differently.
Organ-growth models
Animal studiesA seven-day guinea-pig infusion increased the relative weight of several organs without increasing overall body growth, arguing against simple claims of uniform anabolic benefit.
How it works
LR3 activates the type 1 IGF receptor, which can turn on signaling pathways involved in cell survival, protein synthesis, metabolism, and proliferation. The response depends heavily on the cell type, developmental stage, exposure conditions, and surrounding growth factors.
Native IGF-1 is normally buffered by a family of IGF-binding proteins. LR3 was engineered to bind those proteins much less strongly. Experiments across several species and in bovine embryos show that this altered binding changes where and how strongly the signal appears. It is not simply a longer version of native IGF-1 with an otherwise identical biological profile.
What the research actually shows
A comparative binding study tested native IGF-1, des(1-3) IGF-1, and LR3 in plasma from rats, sheep, pigs, humans, and chickens. LR3 showed the weakest binding to IGF-binding proteins in ligand-blot experiments. The size of that difference varied by species, which is one reason animal results cannot be translated directly into a human claim.
In a seven-day guinea-pig experiment, researchers continuously infused native IGF-1, IGF-2, or LR3. LR3 increased the fractional weights of the adrenal glands, gut, kidneys, and spleen, but it did not significantly improve body-weight gain, feed efficiency, or carcass composition. The study shows biological activity and also provides a clear null result for overall growth.
A bovine embryo study compared 100 ng/mL native IGF-1, 100 ng/mL LR3, and a no-IGF control in a chemically defined culture system. LR3 produced the highest mean blastocyst cell count, 105 cells versus 96 with native IGF-1 and 91 in controls. Native IGF-1 better supported later development, while LR3 more strongly supported early cleavage, so the analog did not outperform native IGF-1 on every measure.
The same embryo study measured the molecular response. LR3 had at least 1,000-fold lower affinity for IGF-binding proteins than native IGF-1 in the reported assays. It increased IGF-1 receptor messenger RNA to 1.3 times the control level, while native IGF-1 reduced it to 80 percent of control. Binding-protein gene responses also differed between the compounds.
LR3 is also used as a cell-culture reagent in biopharmaceutical production. That use supports its ability to promote growth and survival in selected mammalian cell lines under controlled conditions. It does not establish a human performance, recovery, or longevity benefit. No controlled human efficacy trial specific to LR3 was identified for this guide.
Handling & storage
Storage at a glance
Published stability data- Lyophilized
- -20°C, or -80°C for extended storage
- 1-2 years is vendor guidance
- Protect from light and moisture. No regulated finished-product label exists.
- Reconstituted
- 2 to 8°C
- Use within up to 7 days for short-term laboratory work
- For longer storage, laboratory sources recommend frozen single-use aliquots. The common 28-day retail claim is not established stability data.
- Light
- Protect from light.
- Room temperature
- No validated room-temperature excursion window was found.
- Reconstitution
- acidic, carrier-containing, or supplier-specified buffer
- IGF-family proteins can adsorb to surfaces and aggregate. Use low-binding materials and supplier-specific buffer guidance.
Basis: Published stability data. Sources: Elements Arms IGF-1 LR3 laboratory handling, Palmetto Peptides IGF-1 LR3 frozen-aliquot guidance, Peptide Initiative IGF-1 LR3 storage summary
Laboratory guidance treats IGF-1 LR3 as a handling-sensitive protein rather than a typical short peptide. The checked sources call for dry storage at -20°C, or -80°C for extended storage, with protection from light and moisture. A regulated finished-product label does not exist.
After reconstitution, the most conservative checked guidance supports 2 to 8°C for short work lasting up to seven days. For longer laboratory storage, frozen single-use aliquots are preferred. Retail claims of 28 days in bacteriostatic water were not treated as established stability data.
IGF-family proteins can adsorb to container surfaces and aggregate. Supplier-specified, acidic, or carrier-containing buffer guidance and low-binding laboratory materials may be needed. No validated room-temperature excursion window or reliable human LR3 half-life was found.
Safety & cautions
IGF-1 LR3 has no established human safety profile. Because it activates growth and metabolic signaling, plausible risks include low blood glucose, fluid retention, tissue overgrowth, and unwanted stimulation of cells that already have abnormal growth signaling. These are risk considerations, not a complete or measured LR3 adverse-event rate.
IGF signaling is involved in normal growth and in the biology of some cancers. Cell and animal experiments cannot determine whether a particular exposure is safe for someone with cancer, diabetes, cardiovascular disease, or another medical condition. Pregnancy, breastfeeding, childhood use, drug interactions, and long-term exposure have not been adequately studied.
Research-vial quality creates additional uncertainty involving identity, purity, aggregation, sterility, endotoxin, and fill accuracy. LR3 is not FDA approved, and results from regulated prescription IGF-1 products should not be transferred to an unapproved analog.
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Frequently asked questions
Is IGF-1 LR3 FDA approved?
No. IGF-1 LR3 is not an FDA-approved medicine. It is an engineered research analog and should not be confused with approved prescription IGF-1 products.
How is LR3 different from native IGF-1?
LR3 has an amino-terminal extension and an arginine substitution at position 3. These changes greatly reduce binding to IGF-binding proteins and alter its behavior in experimental systems.
Has IGF-1 LR3 been tested in humans?
Controlled human efficacy and safety trials specific to LR3 were not identified for this guide. Most direct evidence comes from cell culture and animal research.
Does LR3 reliably increase muscle growth?
No controlled human evidence establishes that claim. A guinea-pig infusion study found organ-specific growth but no significant improvement in total body growth or carcass composition.
Why do researchers use LR3 in cell culture?
Its weak binding to IGF-binding proteins can make IGF-1 receptor signaling easier to study and can support growth or survival in selected mammalian cell systems.
How should laboratory IGF-1 LR3 be stored?
The checked guidance supports dry storage at -20°C, colder storage for extended periods, protection from light and moisture, and 2 to 8°C for no more than seven days after reconstitution.
Is the often-quoted long human half-life established?
No reliable human pharmacokinetic value specific to LR3 was identified. Retail half-life claims should not be treated as measured human evidence.
Sources
- Lord et al., LR3 binding across plasma from five species
- Conlon et al., seven-day LR3 infusion in guinea pigs
- Prelle et al., native IGF-1 and LR3 in bovine embryos
- Elements Arms IGF-1 LR3 laboratory handling
- Palmetto Peptides IGF-1 LR3 frozen-aliquot guidance
- Peptide Initiative IGF-1 LR3 storage summary
Last reviewed September 17, 2026. This guide is educational and research-focused, not medical advice. IGF-1 LR3 products referenced on PeptidePub are sold by third parties as materials for laboratory research use only, not for human or animal consumption.
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