IGF-1 LR3
Long R3 IGF-1 · LR3 · Long Arg3 IGF-1
IGF-1 LR3 is not a secretagogue. The GHRPs, CJC-1295 and sermorelin all ask your own pituitary to release growth hormone; this supplies the downstream growth factor directly, in a form built to avoid the body's own regulation of it.
Natural IGF-1 circulates almost entirely bound to carrier proteins, which control how much is active at any moment and give it a free half-life of minutes. LR3 carries two modifications that defeat this: a substitution at position three that reduces binding-protein affinity, and a thirteen-residue extension on the N-terminus. The result stays active for something on the order of a day rather than minutes.
That engineering is the whole product and the whole problem. IGF-1 has structural similarity to insulin and cross-reacts with the insulin receptor, so a long-acting, unregulated form can drive blood glucose down. Hypoglycaemia is not a theoretical concern here. It is the mechanism working as designed, in a compound whose effect cannot be called back once injected. Severe hypoglycaemia causes confusion, seizures and loss of consciousness, and there is no human trial establishing a safe dose of LR3 because no human trial of LR3 exists.
How it works
IGF-1 binds the IGF-1 receptor on muscle and other tissue, driving protein synthesis, cell proliferation and differentiation. It is the growth factor that mediates much of what growth hormone does; growth hormone signals the liver to produce IGF-1, and IGF-1 does the work.
The LR3 modifications reduce binding to IGF binding proteins, which normally sequester the great majority of circulating IGF-1 and release it in a controlled way. Bypassing that leaves far more of it free and active for far longer.
Because IGF-1 and insulin are structurally related, IGF-1 also activates the insulin receptor, weakly but meaningfully at the concentrations LR3 can produce. This is what lowers blood glucose, and it is why the risk profile of this compound is not comparable to that of the growth hormone secretagogues it is sold alongside.
The same proliferative signalling that drives muscle growth acts on every cell carrying the receptor. This is the basis of the long-standing epidemiological interest in IGF-1 levels and cancer risk. It is an association observed in populations, not a demonstrated effect of injecting LR3, and nobody can currently quantify it for this compound.
Regulatory status — United States
Not approved for human use in any jurisdiction, and never studied in a human trial. Recombinant IGF-1 itself (mecasermin) is approved for severe primary IGF-1 deficiency, and its labelling carries an explicit hypoglycaemia warning. That warning is the closest thing to clinical safety information this class has.
Last reviewed 16 Aug 2026. Regulatory positions in this category change frequently; we date this line so you can see how current it is.
What it is studied for
Each entry states the evidence behind it. We do not rank indications by effectiveness — for most compounds here, that would be a claim nobody can support.
Muscle growth and recovery
Community practiceThe reason it is bought.
EvidenceNo human trial has studied IGF-1 LR3 for this or any purpose. The rationale is mechanistic and animal data, not clinical evidence.
Cell culture research
ManufacturerWhat it was actually developed for.
EvidenceLR3 is a standard reagent in cell culture, valued for the same stability that makes it attractive to buyers. That is a laboratory application, not a human one.
Identity and clearance
Molecule
- Class
- Recombinant analogue of insulin-like growth factor 1, 70 residues with a 13-residue N-terminal extension
- Molecular weight
- 9111.5 Da
- Length
- 83 amino acids
Arginine substituted for glutamic acid at position 3, plus the extension. Both changes exist to reduce binding-protein affinity.
Pharmacokinetics
ManufacturerFigures for LR3 come from laboratory characterisation and supplier material rather than human pharmacokinetic studies, because none have been done. The contrast with natural IGF-1, whose free half-life is around ten minutes, is the point of the modification.
Dose protocols reported in sources
Displayed for reference only. Every row says where it came from, and a trial protocol and a community convention are not the same kind of information. None of this is fed into the calculator, and none of it is a recommendation.
| Goal | Dose | Frequency | Route | Units, 1 mg vial | Source | Start this protocol |
|---|---|---|---|---|---|---|
| Commonly described community protocol | 20 mcg – 50 mcg | Once daily | SubcutaneousThere is no trial behind any of these numbers. They circulate in community sources, and the range between what people describe as a starting dose and what they describe as a high one is narrow enough that a measuring error crosses it. Given that hypoglycaemia is the failure mode, that is a genuinely dangerous combination. | 10–25 u | Community practice | Start this |
Start this copies a row into a protocol of your own, which you can then edit. Where a source gave a dose range or an ambiguous frequency, those fields arrive empty — we will not pick a number on your behalf.
CheckRows marked community practice describe what people commonly do, drawn from public discussion. They are not derived from any trial and are not evidence that a dose is safe or effective.
Calculator
Work out what to draw
Pre-filled with a 1 mg vial as a worked example. These are not recommended values — change them to match the vial in front of you.
Draw to 8 units on a 1 mL U-100 syringe. That is 0.08 mL, containing 40 mcg of IGF-1 LR3.
8 units sits exactly on a printed line.
Bioalmanac performs arithmetic on values you enter. It does not recommend doses, schedules or compounds, and nothing here is medical advice. Confirm every calculation against your vial and syringe before drawing, and speak with a licensed healthcare provider.
Open this calculation in the full calculator
Units, concentration, bacteriostatic water — the glossary defines the vocabulary, and a unit is not a fixed volume.
Safety
Reported effects
- HypoglycaemiaPublished review
The principal risk, and dose-related
Sweating, shaking, confusion, palpitations, hunger and blurred vision are the warning signs. Severe hypoglycaemia causes seizures and loss of consciousness. Because LR3 is long-acting, an episode is not something you can simply wait out.
- Injection site reactions and lipohypertrophyCommunity practice
Commonly reported
Repeated injection into the same site changes the tissue and also changes absorption, which matters more for a compound with this risk profile.
- Headache and light-headednessCommunity practice
Commonly reported
Worth distinguishing from early hypoglycaemia rather than assuming it is benign.
- Joint and muscle painPublished review
Reported with approved recombinant IGF-1
- Tonsillar enlargement and jaw painPublished review
Reported with approved recombinant IGF-1
A documented effect of the approved product, arising from proliferative signalling in lymphoid tissue.
- Unquantified proliferative riskPublished review
Unknown
IGF-1 signalling drives cell proliferation, and population studies associate higher IGF-1 with some cancers. What deliberately raising it with a long-acting analogue does to that risk is unknown, and there is no study that could currently answer it.
When to stop
- Any sign of low blood sugar: sweating, shaking, confusion, palpitations, sudden hunger, blurred vision. Take fast-acting carbohydrate immediately. If confusion or loss of consciousness occurs, this is an emergency. Call emergency services.
- Repeated hypoglycaemic episodes, even mild ones. This is the compound telling you the dose is wrong, and the next episode may not be mild.
- Any new lump, swelling or unexplained persistent pain.
- Jaw pain, difficulty swallowing, or snoring that is new. All reported with the approved recombinant product.
- Any allergic response: rash, hives, facial swelling or difficulty breathing. Seek urgent care.
- Changes in vision that do not resolve.
Interactions and situations that need care
- Active or previous cancerAvoid
IGF-1 receptor signalling is a direct proliferative signal, and this compound is engineered to sustain it. Of everything on this site, this is the clearest case where the mechanism and the concern are the same thing.
- Diabetes, or anyone using insulin or a sulfonylureaAvoid
IGF-1 lowers blood glucose through insulin receptor cross-reactivity. Adding it to insulin or a drug that raises insulin stacks two glucose-lowering mechanisms, and the approved recombinant IGF-1 product's labelling specifically requires dose adjustment for exactly this reason.
- Using it without a way to treat hypoglycaemiaAvoid
Fast-acting carbohydrate within reach, and someone nearby who knows what you have taken and what low blood sugar looks like. This is not general caution. It is the specific mitigation for the specific way this compound harms people.
- Competing in a tested sportAvoid
IGF-1 and its analogues are named explicitly in WADA's S2 category and are prohibited at all times, in and out of competition. Growth factors are among the substances anti-doping programmes look for most actively.
- Pregnancy and breastfeedingAvoid
No reproductive or developmental safety data, in a compound that drives cell proliferation.
- Closed growth plates uncertain: adolescentsAvoid
IGF-1 acts on growing bone. In anyone whose growth plates have not closed, the effects on skeletal development are unpredictable and irreversible.
SportProhibited by the World Anti-Doping Agency under S2: Peptide Hormones, Growth Factors, Related Substances, at all times, in and out of competition. IGF-1 and its analogues are named explicitly in S2.
What to expect
HonestlyThere is no human efficacy data for this compound, so there is no evidence-based timeline to give. Any site publishing a week-by-week schedule of expected effects has invented it.
- No human trial of IGF-1 LR3 exists. Every dose figure in circulation is community convention, and the interval between a common starting dose and a high one is small enough that a reconstitution error crosses it.
- Hypoglycaemia is the failure mode that puts people in hospital, and because the compound is long-acting, an episode cannot be waited out. Fast-acting carbohydrate within reach is not optional.
- The approved recombinant IGF-1 product carries an explicit hypoglycaemia warning in its labelling. That is a regulator describing this exact mechanism in a supervised clinical setting.
- Local effects at the injection site are frequently described, and the claim that this produces site-specific muscle growth is not supported by any human data.
- The proliferative concern cannot be quantified from anything currently published. This is not the same as it being small.
Storage and handling
- Freeze-dried powder
- Refrigerated at 2–8 °C, protected from light.
- After mixing
- Refrigerated at 2–8 °C. Do not freeze once mixed. Larger proteins are less forgiving of temperature swings than short peptides.
- Long-term, frozen
- Unopened powder is stable at −20 °C or colder.
With other peptides
- HGH (Somatropin)caution
Growth hormone works largely through IGF-1. Adding a long-acting IGF-1 analogue on top compounds the proliferative signal from both ends of the same axis.
- PEG-MGFcaution
Both are IGF-1 derivatives engineered to escape normal clearance. Running them together compounds the same proliferative signalling from two directions, with no human data on either.
- MK-677caution
MK-677 raises IGF-1 by driving growth hormone, and also worsens insulin sensitivity on its own. Adding exogenous long-acting IGF-1 on top compounds both the proliferative signal and the glucose effects, from two directions at once.
- CJC-1295caution
A GHRH analogue raises IGF-1 through the normal, regulated pathway. Adding an unregulated long-acting analogue means the body's own control of IGF-1 availability is being bypassed while it is also being driven, and nothing establishes what that combination does.
- Follistatin-344caution
Both drive muscle growth through unregulated pathways. One supplies an accelerator; the other removes a brake. Neither has human safety data, the proliferative concerns compound, and no study has looked at the combination.
- Cyclic Glycine-Prolinecaution
These point in opposite directions. LR3 is engineered specifically to escape binding protein regulation; cGP is claimed to restore it. Nothing establishes what taking both does.
Checking your vial
Research chemicals carry no manufacturing standard, so what the vial looks like is often the only quality signal available before you use it. More on assessing quality and COAs.
White cake, clear solution
Standard for a lyophilised protein.
Collapsed or melted cake
Heat exposure in transit. An 83-residue protein is more vulnerable to this than a hexapeptide.
Cloudy solution, or any visible particles
Protein aggregation or contamination. Do not use it.
Questions
- How dangerous is the hypoglycaemia risk?
- It is the reason this page is written the way it is. IGF-1 cross-reacts with the insulin receptor and lowers blood glucose, and LR3 is engineered to stay active for around a day. Severe hypoglycaemia causes seizures and unconsciousness. The approved recombinant IGF-1 medicine carries an explicit warning about it, given under supervision with dose titration. None of that applies to a research chemical.
- Does injecting it into a specific muscle grow that muscle?
- That is the common claim and no human data supports it. Local injection-site effects are reported, but 'site-specific growth' as an outcome has not been measured in people.
- How is this different from the GHRPs on this page?
- Completely. A GHRP asks your pituitary for a growth hormone pulse — bounded by what your pituitary can release — and cleared within hours. LR3 supplies the downstream growth factor directly, in a form designed to escape the body's regulation of it, lasting about a day. The safety questions are not comparable.
- Is it the same as the approved IGF-1 medicine?
- No. Mecasermin is recombinant human IGF-1, unmodified, approved for severe primary IGF-1 deficiency and given under supervision with glucose monitoring. LR3 is a modified analogue built to last longer and evade binding proteins, and it has never been through a human trial.
References
Characterisation of Long R3 IGF-1: reduced binding protein affinity and extended activity
Protein science and supplier characterisation literature, 1993 · Laboratory characterisation and cell culture work
In vitro
Confirmed that the position-3 substitution and N-terminal extension substantially reduce IGF binding protein affinity, producing a more potent and longer-acting analogue in cell culture. No human pharmacokinetic data exists.
Mecasermin (recombinant human IGF-1) prescribing information: hypoglycaemia and adverse effects
FDA prescribing information, 2019 · Regulatory labelling based on clinical trial data
Humans with severe primary IGF-1 deficiency
Carries an explicit hypoglycaemia warning requiring food intake before or with each dose and dose adjustment alongside insulin. Also documents tonsillar hypertrophy, injection site lipohypertrophy and joint pain. The closest available clinical safety information for the IGF-1 class.
Circulating IGF-1 concentrations and cancer risk: pooled epidemiological analyses
Cancer epidemiology literature, 2010 · Pooled analysis of prospective cohort studies
Humans
Higher circulating IGF-1 is associated with increased risk of several cancers, notably prostate and breast. Observational association in populations with naturally varying levels; it does not establish what injecting a long-acting analogue does, and no study addresses that question.
Commonly reported community protocols
Bioalmanac editorial summary of public community sources, 2026 · Not a study
Records the dose and timing patterns described in public discussion. There is no trial behind any of them, and they carry no evidential weight about safety or effect.
Related compounds
HGH (Somatropin)
An approved medicine for people with a growth hormone deficiency. Used without that diagnosis it is a controlled substance in the United States, and the anti-ageing claims it is sold on were retracted by their own author.
PEG-MGF
A splice variant of IGF-1 released by damaged muscle, pegylated to last longer. No human trials, and the same proliferation concern as everything in the IGF family.
MK-677
An orally active ghrelin receptor agonist that raises growth hormone and IGF-1. Not a peptide, and not injected. It is a small molecule taken by mouth.
CJC-1295
A GHRH analogue that raises growth hormone by amplifying the body's own release signal. Sold in two forms whose durations differ by two orders of magnitude.
Next
What to do with IGF-1 LR3
- Keep a record of itTurn a dose and a schedule into a protocol, then log what you actually take. IGF-1 LR3 is filled in for you.
- See what it costsPer-milligram prices read from vendor sites and confirmed by a person, so vial sizes compare.
- Check a combinationWhat our profiles record about IGF-1 LR3 alongside each other compound — including the pairs where nothing is recorded.
Keep this page honest
If something here is wrong, out of date, or missing a source, tell us and we will fix it and say that we did.
This page is educational. It describes what published research reports, not what you should do. Peptides discussed here are largely not approved for human use, and nothing on Bioalmanac is medical advice. No clinician reviews these pages.
Page last updated 16 Aug 2026