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Growth hormone axis

IGF-1 LR3 (Long R3 IGF-I)

Also known as Long R3 IGF-I, LR3-IGF-I, Long [Arg3] IGF-I, LONG-(ARG3)INSULIN-LIKE GROWTH FACTOR-I

Preclinical only

Synthetic IGF-1 receptor agonist (IGF-1 analogue); non-approved research-chemical peptide

Not FDA-approved. Not on FDA's 503A category lists (May 14, 2026). Source, May 14, 2026

Identity. IGF-1 LR3 is an engineered IGF-1 analogue (Arg substituted for Glu at position 3, plus an N-terminal extension) with markedly reduced IGF-binding-protein affinity. It is not mecasermin (Increlex, rhIGF-1), which is a different molecule with an approved label. Never convert between the two. The mecasermin label starts at 0.04 mg/kg to 0.08 mg/kg twice daily (about 2.8-5.6 mg per injection at 70 kg), roughly 100x or more above the 10-20 mcg/day LR3 practice start. LR3 was 2.5-3x more potent than IGF-I in diabetic rats (PMID 7683875). Doses are in mcg only. U-100 syringe 'units' are volume marks, not IU, and LR3 is never dosed in IU. LR3 is also not des(1-3)-IGF-I, R3-IGF-I or MGF. A published case report found a black-market vial sold as LR3 that contained His-tagged Long-R3-IGF-I, and anti-doping analyses found oxidized forms in black-market products. Identity and purity vary by supplier, so require a certificate of analysis with mass-spectrometric identity and purity. The formulary lists a 1 mg vial and also a blend. No source states the LR3 content (mcg per vial) of the blend. Do not calculate blend doses until the pharmacy label gives LR3 mcg per vial. No source supports dosing LR3 inside a blend.

At a glance

These dosages are a helpful guide, not a prescription. Every clinician is expected to do their own due diligence before prescribing.

No established human dose

No peer-reviewed human studies of IGF-1 LR3 were found, and a 2026 narrative review places it in its lowest evidence tier (no human studies). The located LR3 literature is cell-line, animal or analytical work: diabetic rats (LR3 2.5-3x more potent than IGF-I in restoring growth, PMID 7683875), tumour-bearing rats (tumour growth increased, especially by LR3, PMID 8053901), neonatal pigs (LR3 infusion lowered measured plasma IGF-I, PMID 12067429), mouse and fetal sheep work, and anti-doping analytics (PMID 33587816). Human dose figures come only from forum, vendor and clinic-education statements, which the sources themselves describe as not coming from any clinical trial. There are no human study doses. The human safety signals below come from native rhIGF-I or mecasermin. They are context only and never a basis for dosing.

No clinical study supports any LR3 dose; the only published ranges are forum-reported. Never apply mecasermin (Increlex) label doses to LR3: hypoglycemia can be life-threatening.
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What clinics and vendors publish

These ranges come from clinic and vendor publications, not studies.

Clinic-reportedCommunity-reported

Every practice number here is anecdotal or comes from non-clinical sources. The 2026 review states that no peer-reviewed clinical studies report specific dosing regimens in humans. The 2026 review states these values 'MUST NOT be interpreted as clinically validated, regulatory-approved, or safe for use'. No trial, label or guideline supports any dose. Figures vary between sources (10-20, 20-40, up to 100 mcg/day). Never apply mecasermin (Increlex) label doses to LR3. The label starts at 0.04-0.08 mg/kg twice daily (about 2.8-5.6 mg per injection at 70 kg, i.e. 3-6 whole 1 mg vials), roughly 100x or more above LR3 practice doses, and LR3 was 2.5-3x more potent than IGF-I in rats. Applying a label dose to LR3 risks life-threatening hypoglycemia. The mecasermin label is context for safety signals only and must never be used to derive an LR3 dose.

StartClinic-reported
20 mcg/day (vendor protocol site: tier 'used to gauge tolerance and hypoglycemic response'); clinician-education site: 'micro-dosing, around 10-20 mcg per day'
TitrationClinic-reported
No stepwise titration schedule found. Vendor site lists community tiers of 20, 20-40, 40-80 and 80-100 mcg/day; the 80-100 tier is annotated 'Reported by advanced users; side-effect frequency rises.' Do not titrate on serum IGF-1 (see safety.monitoring).
TypicalClinic-reported
20-40 mcg/day (forum-derived, per 2026 review table); vendor site calls 20-40 mcg/day the 'Most-cited beginner range'
CeilingClinic-reported
Community protocols 'cluster between 20 and 100 mcg per day' (vendor site, not from a trial); same site reports 'Diminishing returns commonly reported above ~50-60 mcg/day'. No clinical-guideline ceiling exists. Tools should warn hard above 100 mcg/day, the top of every cited range, and block mg/kg units for LR3.
FrequencyClinic-reported
Once daily
RouteClinic-reported
Subcutaneous or intramuscular injection (SC most common per clinician-education site)
TimingClinic-reported
Post-workout on training days (forum-derived). Take with carbohydrates and do not inject without eating because of hypoglycemia risk (clinician-education site); the vendor site pairs dosing with 30-50 g of fast-acting carbohydrate within roughly 30 minutes (vendor, not trial-based). Almost all sources advise against pre-bed dosing because hypoglycemia during sleep is harder to detect (vendor site). Analogue labeling (mecasermin, not LR3): give within +/-20 minutes of a meal or snack and withhold the dose if the patient cannot eat.
CycleClinic-reported
4-6 weeks on, followed by an equal off-period (2026 review table, forum-derived); clinician-education site: break of 'equal or longer length'
  • Clinic-reportedProfessional education2
    Suggested protocols often use micro-dosing, around 10–20 mcg per day, for 4–6 weeks at a time.
  • Clinic-reportedProfessional education2
    Injection is most commonly subcutaneous, using an insulin syringe into areas with reliable circulation, such as the abdomen or thigh.
  • Community-reportedOther web source1
    Bodybuilding-related forums: SC or IM 20-40 µg/day, once daily, ideally post-workout; typical cycle: 4–6 weeks on, followed by an equal off-period
  • Community-reportedVendor page3
    Community protocols generally cluster between 20 and 100 mcg per day.
  • Community-reportedVendor page3
    Used to gauge tolerance and hypoglycemic response.
  • Community-reportedVendor page3
    Diminishing returns commonly reported above ~50-60 mcg/day.
  • Community-reportedVendor page3
    Almost all sources advise against pre-bed dosing because hypoglycemia during sleep is harder to detect.
  • Community-reportedOther web source4
    INCRELEX should be administered shortly before or after (± 20 minutes) a meal or snack.

Safety

Serious warnings

  • No FDA label or boxed warning exists for IGF-1 LR3, which is not an approved product. For mecasermin, a distinct approved IGF-1 product, the label states 'Severe hypoglycemia leading to hypoglycemic seizures has been observed with INCRELEX treatment.' This is context on class biology, not LR3 data.4
  • Hypoglycemia is the main acute concern reported for off-label use: 'reported adverse effects in off-label settings frequently centre on insulin-mimetic activity (e.g., symptoms suggestive of hypoglycaemia)', though 'many such reports originate from non-clinical sources and should be treated cautiously'.1
  • Tumour-promotion signal (animal, LR3-specific): in rats bearing a mammary adenocarcinoma, 'Tumour growth was increased by the IGFs, especially by LR3-IGF-I, even though these peptides did not promote growth of the adenocarcinoma in cell culture.' For mecasermin, the label reports tumours observed 'more frequently in patients who received INCRELEX at higher than recommended doses' (analogue data). LR3 has no human long-term safety data. The 2026 review frames cancer risk as 'theoretical but clinically relevant'.5

Contraindications

  • Active or suspected malignancy, or a history of malignancy: do not use. This comes from analogue and animal data, not an LR3 label. The mecasermin label states 'INCRELEX is contraindicated in pediatric patients with malignant neoplasia or a history of malignancy' (pediatric population), and LR3 increased tumour growth in tumour-bearing rats (PMID 8053901). No LR3-specific contraindication data exist.4
  • Known hypersensitivity to the product or its excipients. This comes from the mecasermin label ('INCRELEX should not be used by patients who are allergic to mecasermin (rhIGF-1)'). It is analogue data, not an LR3 label.4

Adverse effects

  • A review of GH-IGF-1-axis performance peptides (including IGF-1 LR3) lists these reported class adverse effects: endocrine and metabolic disturbances including dysglycaemia, fluid retention, myalgia/arthralgia and injection-site reactions. These are not LR3-specific trial data.1
  • A clinician-education page says 'patients may experience hypoglycemia if they inject without eating'.2
  • Human class data (native rhIGF-I, not LR3; randomized trial, n=223, type 1 diabetes): higher doses 'were associated with unacceptable levels of adverse events, including edema, jaw pain, and early worsening of retinopathy.' Use caution in pre-existing diabetic retinopathy (analogue data).6

Monitoring

  • A clinician-education page says 'careful screening and ongoing monitoring are so important' and advises use 'only under proper medical supervision'. It gives no glucose-monitoring method or frequency.2
  • Obtain baseline fasting glucose or HbA1c (2026 review: 'Fasting glucose or HbA1c worth obtaining regardless of compound class'). The mecasermin label (analogue data, not LR3) calls for preprandial glucose monitoring 'at treatment initiation and until a well-tolerated dose is established'. Check fingerstick glucose before the dose, and when symptomatic, at the start and after every dose change. The label also calls for funduscopic examination 'at the initiation and periodically' (label section 5.3).4
  • Do not titrate on, or interpret, serum IGF-1. In neonatal pigs 'Infusion of LR3IGF-I decreased plasma IGF-I concentrations'. Routine immunoassays are not validated for LR3, so a normal or low IGF-1 does not show low exposure.7
  • A vendor protocol site says research practice 'pairs dosing with 30-50 grams of fast-acting carbohydrates within roughly 30 minutes' (an administration tip; see the timing entry under practice).3
  • Product identity and purity risk: a case report identified His-tagged Long-R3-IGF-I in an injection vial from the black market and noted that the effects of the His-tagged product in humans 'have not been elucidated'. Anti-doping analysis found 'Abundant signs of lower quality, oxidized peptide forms' in black-market products. Require a certificate of analysis with mass-spectrometric identity and purity, and source only from a licensed compounding pharmacy.8

Interactions

  • Insulin, insulin secretagogues (sulfonylureas, meglitinides) and other glucose-lowering agents: additive hypoglycemia is expected. In a native rhIGF-I trial, daily insulin use fell 11-19% (analogue data, not LR3). Mecasermin patient information says 'A change in dose may be needed for these medicines.' Avoid LR3 in these patients, or co-manage with glucose monitoring.6

Handling

Reconstitution

No authoritative source was found for the diluent type. Get the diluent and storage instructions from the pharmacy's certificate of analysis or compounded-product label. The syringe-reading rules below are arithmetic, not sourced guidance. In a 1 mg vial, 1 mL of diluent gives 1,000 mcg/mL, so a 10 mcg dose is 0.01 mL (1 unit on a U-100 syringe), and misreading one mark doubles or halves the dose. Use at least 2 mL of diluent (500 mcg/mL; 20 mcg = 0.04 mL = 4 units) or 3 mL. Always show the dose in mcg, mL and U-100 syringe units side by side. State that syringe units are volume marks, not IU. Warn when a calculated draw is under 2 units. Do not use mg/kg dosing for LR3. At 20-100 mcg/day one 1 mg vial lasts 10-50 doses.9

Evidence

No peer-reviewed human studies of IGF-1 LR3 were found, and a 2026 narrative review places it in its lowest evidence tier (no human studies). The located LR3 literature is cell-line, animal or analytical work: diabetic rats (LR3 2.5-3x more potent than IGF-I in restoring growth, PMID 7683875), tumour-bearing rats (tumour growth increased, especially by LR3, PMID 8053901), neonatal pigs (LR3 infusion lowered measured plasma IGF-I, PMID 12067429), mouse and fetal sheep work, and anti-doping analytics (PMID 33587816). Human dose figures come only from forum, vendor and clinic-education statements, which the sources themselves describe as not coming from any clinical trial. There are no human study doses. The human safety signals below come from native rhIGF-I or mecasermin. They are context only and never a basis for dosing.

Mechanism

Engineered IGF-1 analogue that acts at the IGF-1 receptor to activate PI3K-Akt and MAPK/ERK signalling (protein synthesis, proliferation, survival). Reduced binding to IGF-binding proteins compared with native IGF-1 is shown in model systems. Effects in humans are presumed from IGF-1 biology and have not been demonstrated.110

Availability

Amounts offered

  • 1 mg

Custom strengths on request.

Blends that include IGF-1 LR3 (Long R3 IGF-I)

References

According to PubMed

  1. 1The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration.Front Endocrinol (Lausanne) 17:1822475 (narrative review; full text PMC13322892), 2026
  2. 2IGF-1 LR3 in Aesthetic and Anti-Aging Medicine: Benefits and Risks (Hubmed Team; states it is intended for licensed medical professionals)hubmeded.com, 2026
  3. 3IGF-1 LR3 Peptide Dosing Guide (Peptide Dosing Protocols; supply links may earn commission; self-described human-researched and AI-assisted)peptidedosingprotocols.com, 2026
  4. 4INCRELEX (mecasermin) injection, solution - prescribing information (Revised 7/2025); distinct molecule from IGF-1 LR3, cited as analogue context only, never for LR3 dosingDailyMed / Ipsen Biopharmaceuticals (set id a8b27a1b-a611-4f91-ad22-76d4b390c3ae), 2025
  5. 5Effects of insulin and insulin-like growth factors on protein and energy metabolism in tumour-bearing rats.Biochem J 301(Pt 3):769-75 (rat), 1994
  6. 6Cotherapy with recombinant human insulin-like growth factor I and insulin improves glycemic control in type 1 diabetes. RhIGF-I in IDDM Study Group.Diabetes Care 22(4):585-92 (randomized trial of native rhIGF-I, n=223; analogue data, not LR3), 1999
  7. 7Insulin-like growth factor-I and analogues increase growth in artificially-reared neonatal pigs.Br J Nutr 87(6):587-93 (neonatal pig), 2002
  8. 8Detection of His-tagged Long-R3-IGF-I in a black market product.Growth Horm IGF Res 20(5):386-90, 2010
  9. 9Detection of LongR-IGF-I, Des(1-3)-IGF-I, and R-IGF-I using immunopurification and high resolution mass spectrometry for antidoping purposes.Drug Test Anal 13(7):1256-1269 (rat IM 100 mcg/kg: LongR-IGF-I disappeared after 4 h, fragments detected up to 16 h; no human half-life), 2021
  10. 10NKX3.1 activates expression of insulin-like growth factor binding protein-3 to mediate insulin-like growth factor-I signaling and cell proliferation.Cancer Res 69(6):2615-22 (in vitro; describes long-R3-IGF-I as 'an IGF-I variant peptide that does not bind to IGFBP-3'), 2009
  11. 11Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (Categories 1, 2, 3; 'Updated May 14, 2026')U.S. FDA, 2026
  12. 12Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act (content current as of 05/14/2026)U.S. FDA, 2026
  13. 13Insulin-like growth factor-I and more potent variants restore growth of diabetic rats without inducing all characteristic insulin effects.Biochem J 291(Pt 3):781-6 (rat), 1993
  14. 14World Anti-Doping Code International Standard: Prohibited List 2026 (S2.3 Growth Factors and Growth Factor Modulators); federation-hosted copy of WADA's official PDF, text extracted and read directlyWADA (copy hosted at segas.gr), 2026

Last reviewed 2026-10-14. 19 figures checked against their sources. How this works