Compound record · Growth hormone axis
IGF-1 LR3
Also Long R3 IGF-1 · LR3 IGF-I · LONG R3 IGF-I · IGF-1 Long R3 · LR3 · IGF-1 LR3 (research chemical)
Engineered IGF-1 analogue (laboratory reagent)
Laboratory IGF-1 analogue with no human trials and serious hypoglycaemia risk
Record reviewed 1 September 2026 · 5 references
- Class
- Engineered IGF-1 analogue (83 amino acids)
- Human trials
- None — developed as a cell-culture reagent
- Key risk
- Severe hypoglycaemia (insulin-like action)
- Related medicine
- Mecasermin (Increlex) — different molecule, children only
- Status
- Not authorised anywhere; WADA-prohibited (S2)
01 Overview
What IGF-1 LR3 is
Summary
IGF-1 LR3 (Long R3 IGF-1) is an 83-amino-acid engineered version of insulin-like growth factor 1 with a 13-amino-acid extension and an arginine substitution at position 3 that cut its binding to IGF-binding proteins by more than a thousand-fold, making it far more potent and longer-acting in cell culture. It was designed as a reagent for growing cells in laboratories and biopharmaceutical manufacturing and has never been given to humans in a clinical trial. Native IGF-1 (mecasermin, Increlex) is an approved medicine for severe childhood IGF-1 deficiency, but it is a different molecule with a monitored dosing regimen — LR3 is not authorised anywhere.
Mechanism
Activates the type 1 IGF receptor (and, at high concentrations, the insulin receptor) to drive cell growth, protein synthesis and glucose uptake into muscle and fat. Because the modifications stop it being held inactive by IGF-binding proteins, almost all of the injected peptide is free and biologically active — which is why it is potent in the laboratory and why its insulin-like glucose-lowering effect is expected to be stronger and less predictable than that of natural IGF-1.
02 Evidence by goal
What has been shown, for which goal
Grades follow one scale across the site. Insufficient overall means: no reliable human evidence for this use — animal or laboratory data only.
Muscle & recovery
InsufficientNo human studies of any kind. Native IGF-1 (mecasermin) modestly increases lean mass in children with severe IGF-1 deficiency; this does not translate to LR3 in healthy adults.
Athletic performance
InsufficientNo human data; IGF-1 and its analogues are prohibited at all times under the WADA list (S2).
Injury & recovery support
InsufficientAnimal and cell-culture data only; no human study has examined tissue healing.
Fat loss / body composition
InsufficientNo human data. Native IGF-1 lowers glucose and causes fat build-up at injection sites (lipohypertrophy) rather than fat loss.
03 Regulatory status
Where it is authorised, and for what
Status is recorded per jurisdiction from regulator sources and reviewed by hand. It is never inferred from another region's decision.
United Kingdom
Not authorisedNot authorised as a medicine; sold only as an unregulated 'research chemical'.
No MHRA licence. Mecasermin (Increlex) — native IGF-1, a different molecule — is licensed in the UK for severe primary IGF-1 deficiency in children and is prescription-only; it is not interchangeable with LR3.
04 Dosing research
What the evidence says about exposure
Published human studies and the doses, routes and durations they used — reported as research information, not a recommendation.
Research information — not a recommendation. These are the exposures used in published human studies, reported so you can see what has been tested. They are not dosing instructions and do not apply to any individual.
No studies recorded
No published human dosing studies
There are no human dose-finding, safety or efficacy studies of IGF-1 LR3 — it has only been used in cell culture and in animal experiments. Doses circulating online (typically 20–100 µg daily) are not derived from any trial. Dosing data for mecasermin (native IGF-1, 0.04–0.12 mg/kg twice daily in children with severe primary IGF-1 deficiency, given with food and with glucose monitoring) cannot be transferred, because LR3's thousand-fold lower binding to IGF-binding proteins means far more free, active peptide per microgram and a stronger, less predictable glucose-lowering effect.
05 Safety
Adverse effects and contraindications
Common effects seen in trials or reports, serious effects that warrant urgent review, and conditions under which use is not appropriate or needs assessment.
Common adverse effects
- Hypoglycaemia — shakiness, sweating, hunger, confusion (28% of children on mecasermin; expected to be more pronounced with LR3)
- Headache (44% with mecasermin)
- Fat build-up at injection sites (lipohypertrophy)
- Nausea and vomiting
- Joint and limb pain
- Dizziness
- Enlarged tonsils and adenoids, snoring (with prolonged use)
- Swelling and water retention
Serious adverse effects
- Severe hypoglycaemia with seizures or loss of consciousness (6 of 115 children with hypoglycaemia on mecasermin had seizures)
- Intracranial hypertension (about 1% with mecasermin)
- Sleep apnoea from lymphoid tissue enlargement
- Acromegaly-like growth of the jaw, facial bones, hands and feet with sustained excess
- Possible promotion of existing tumours — IGF-1 caused mammary carcinoma and skin tumours in rat carcinogenicity studies
- Anaphylaxis and other allergic reactions
- Completely unknown long-term effects — no human safety data exist at any dose
Contraindications
- CancerDo not use
IGF-1 signalling drives growth in many tumour types, and mecasermin is contraindicated in active or suspected neoplasia or any condition that raises cancer risk. Any current or previous cancer should be regarded as excluding use.
- DiabetesDo not use
Treated as absolute because of an unpredictable insulin-like glucose-lowering effect with no human safety data; hypoglycaemia was very common (28%) even with monitored mecasermin, and interaction with insulin or sulfonylureas could be severe.
- Acromegaly or pituitary tumourDo not use
Adding an IGF-1 analogue to a condition already defined by GH/IGF-1 excess is inappropriate.
- Raised intracranial pressureCaution
Intracranial hypertension with papilloedema, headache and vomiting has been reported with mecasermin (about 1% of treated children) and with GH therapy.
- Sleep apnoeaCaution
Mecasermin causes tonsillar and adenoidal enlargement with snoring and sleep apnoea; an IGF-1 analogue is expected to worsen existing sleep apnoea.
- Hormonal disorderCaution
Pituitary, adrenal or thyroid disorders alter glucose handling and IGF-1 physiology; endocrine assessment is required before any GH-axis intervention.
Do not use = should not be used · Caution = needs assessment
06 Interactions
Medicine classes that need review
Grouped by how seriously the combination should be taken. Class labels match the medicines questionnaire in the assessment.
- Major
- Moderate
- Minor
Major
Combination should be reviewed by a prescriber before use.
Insulin
Lantus, NovoRapid, Humalog, Tresiba
Additive glucose lowering — the combination could cause severe, prolonged hypoglycaemia.
Sulfonylurea
Gliclazide, glimepiride, glipizide
Additive hypoglycaemia risk with no data to guide dose adjustment.
Growth hormone
Somatropin
Additive IGF-1 exposure on top of GH-driven IGF-1; increased risk of acromegaly-like effects and hypoglycaemia.
Moderate
Monitoring or dose review is usually advised.
Other glucose-lowering medicine
Metformin, SGLT2 inhibitors, DPP-4 inhibitors
Glucose-lowering effects add up; frequent monitoring would be required.
GLP-1 / incretin medicine
Ozempic, Wegovy, Mounjaro, Saxenda
Reduced food intake on GLP-1 medicines increases the danger of IGF-1-induced hypoglycaemia, which depends on eating around each dose.
Corticosteroid
Prednisolone, dexamethasone, hydrocortisone
Glucocorticoids antagonise IGF-1's growth effects and raise glucose, making glucose swings less predictable.
Minor
Generally compatible; awareness is sufficient.
Testosterone / anabolic hormone
Testosterone gel or injection
Frequently combined in 'performance' regimens; no human data and additive anabolic-hormone risk.
07 Pregnancy & breastfeeding
Status in pregnancy
No human or animal reproductive data for LR3. An untested growth factor with hypoglycaemic effects cannot be supported in pregnancy or while breastfeeding.
08 Monitoring
What is usually monitored
Parameters that trials and product information track. A clinician decides what applies to an individual.
- 01Blood glucose before and for several hours after any dose — hypoglycaemia is the dominant acute risk
- 02IGF-1 — standard assays were validated for native IGF-1 and may not measure LR3 reliably, so a 'normal' result does not exclude excess
- 03Eye examination for headaches, visual disturbance or vomiting (intracranial hypertension)
- 04Snoring, daytime sleepiness and other sleep-apnoea symptoms
- 05Changes in jaw, facial features, ring or shoe size
- 06Age-appropriate cancer screening and prompt review of any new lump or symptom
09 Combinations
What is known about combining it
Notes on pairing with other compounds in the directory: whether the combination has been studied in people, and where mechanisms overlap.
Somatropin
No human studies
Overlap · Additive IGF-1 exposure and compounded hypoglycaemia risk.
No human data; combines a licensed, monitored medicine with an untested laboratory reagent acting on the same pathway.
CJC-1295
No human studies
Overlap · Additive IGF-1 exposure — CJC-1295 raises IGF-1 for days at a time.
No human data for either compound in this setting; both are unlicensed research chemicals.
Ipamorelin
No human studies
Overlap · Additive IGF-1 exposure via GH release.
No human data; both are unlicensed research chemicals.
Tesamorelin
No human studies
Overlap · Additive IGF-1 exposure on top of a medicine whose label already warns about IGF-1 elevation.
No human data.
Sermorelin
No human studies
Overlap · Additive IGF-1 exposure via GH release.
No human data.
Semaglutide
No human studies
Overlap · Both lower glucose; appetite suppression increases the risk of IGF-1-induced hypoglycaemia.
No human data on the combination.
BPC-157
No human studies
Marketed together as 'recovery' stacks; no human data for either compound in this setting.
TB-500
No human studies
No human data on the combination; TB-500 itself has no human efficacy data.
Discuss any proposed combination with a qualified healthcare professional.
10 Source considerations
Supply, quality and legitimacy
How the compound reaches people in practice, and what that means for product quality.
- 01Sold only as a 'research chemical' for laboratory use; no manufacturer intends it for human injection and no product has sterility, endotoxin or potency assurance for that purpose.
- 02Independent testing of online peptides has found vials labelled IGF-1 LR3 containing a different peptide, a fraction of the stated amount or nothing active.
- 03Microgram-to-milligram dosing errors with an insulin-like peptide can cause life-threatening hypoglycaemia.
- 04Increlex (mecasermin) is a prescription medicine for children with a specific deficiency; it is not the same molecule and is not a legitimate route to LR3.
11 Questions for your clinician
Take these to your appointment
Specific to this compound. The personal assessment adds questions drawn from your own history and medicines.
- 01Is there any reason to think I have IGF-1 or GH deficiency, and if so what licensed, monitored treatment would be appropriate instead?
- 02How would we detect and manage hypoglycaemia from a peptide that has never been dosed in humans?
- 03Do I have any cancer history, diabetes, sleep apnoea or headaches with visual symptoms that make this especially risky?
- 04Would standard IGF-1 blood tests even detect this analogue?
- 05Am I subject to anti-doping rules in any sport?
The personal assessment tailors this list to your responses.
12 Alternatives
Compounds with stronger evidence or firmer regulatory footing
Listed for overlapping goals. Whether any is appropriate depends on your history — the assessment maps that for you.
13 References
Sources behind this record
Regulator documents and peer-reviewed publications used to derive every grade and statement above.
- 01Francis GL et al. Novel recombinant fusion protein analogues of IGF-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. J Mol Endocrinol 1992;8:213–223
- 02Repligen — LONG R3 IGF-I: structure, IGFBP affinity and use in CHO cell culture (technical poster)
- 03Increlex (mecasermin) Summary of Product Characteristics (UK) — native IGF-1, for risk extrapolation
- 04Endocrine Society — Hormones and Aging: Scientific Statement (2023)
- 05WADA Prohibited List — S2 peptide hormones, growth factors, related substances and mimetics
The Peptide Checkup provides educational information and a structured summary of published research and regulatory status. It is not medical advice, does not diagnose or treat any condition, and does not replace a consultation with a qualified healthcare professional.
Personal assessment
Check IGF-1 LR3 against your history
Seven minutes of structured questions about your goal, history and medicines, mapped against this record by a deterministic, clinician-reviewable rules engine. The report tells you when not to buy.