IGF-1 LR3: 2026 Dosing, Safety & Regulatory Status

IGF-1 LR3 (Long Arg³ Insulin-like Growth Factor-1) is a modified analog of native human IGF-1, engineered in the late 1980s and early 1990s as a research reagent to study IGF-1 receptor (IGF-1R) signaling with minimal interference from circulating IGF-binding proteins. Two structural changes — an arginine substitution at position 3 of the mature peptide and a 13 amino acid N-terminal extension — reduce its binding-protein affinity by roughly 600-fold and stretch its plasma half-life from about 15 minutes (native IGF-1) to roughly 20 hours. Those changes also make it the IGF-1 analog most often discussed in bodybuilding and biohacker forums, where it is used off-label and outside any clinical supervision. This guide covers the molecule’s origin and mechanism, how it differs from native IGF-1 and from mecasermin, what the published rodent literature shows about anabolic effects and organ growth, dosing patterns reported in non-medical use, reconstitution math, the real safety concerns (hypoglycemia and theoretical cancer-promotion risk), and the current U.S. regulatory status. IGF-1 LR3 is not approved for human therapy and is not legally compoundable.

Table of Contents

• What Is IGF-1 LR3?
• How IGF-1 LR3 Differs From Native IGF-1
• Mechanism of Action
• Dosing Patterns Reported in Non-Medical Use
• Reconstitution Math
• Pre- and Post-Workout Timing
• What the Published Evidence Actually Shows
• Safety Profile
• Drug interactions
• Cycle Lengths
• Lab Monitoring
• Storage & Travel
• 2026 Regulatory Status
• FAQ
• References

What Is IGF-1 LR3?

IGF-1 LR3 is an 83 amino acid recombinant protein that retains the biological activity of native IGF-1 at the IGF-1 receptor while binding very poorly to the six circulating IGF-binding proteins (IGFBP-1 through IGFBP-6). The molecule was developed at the University of Adelaide and at GroPep (later acquired by Novozymes and now part of Repligen) in collaboration with several Australian academic groups in the late 1980s. The original commercial use was as a cell-culture supplement: because LR3 IGF-1 does not get sequestered by IGFBPs in serum, it is roughly three times more potent than native IGF-1 in driving cell proliferation in bioreactors, which is why it is still the standard insulin replacement in many monoclonal antibody and recombinant protein manufacturing platforms.

That same property — freedom from IGFBP buffering — is what made LR3 IGF-1 attractive to bodybuilders and biohackers a decade later. In the body, more than 95 percent of native IGF-1 circulates bound to IGFBP-3 and the acid-labile subunit, and that ternary complex is the body’s main reservoir and brake on IGF-1 activity. LR3 IGF-1 bypasses that brake, producing free, bioactive ligand at the IGF-1R for the full ~20-hour plasma half-life of the molecule.

It is important to be precise about names. “IGF-1 LR3,” “Long R3 IGF-1,” “LR3 IGF-I,” and “LONG®R3 IGF-I” refer to the same molecule. Mecasermin (brand name Increlex) is recombinant human IGF-1 — structurally identical to native IGF-1 with no modifications — and is a completely different product with FDA approval for severe primary IGF-1 deficiency in children. Mecasermin rinfabate (the IGF-1/IGFBP-3 binary complex marketed briefly as iPlex) is a third, distinct product. The peptides sold online as “IGF-1 LR3” are not Increlex and are not equivalent to it.

How IGF-1 LR3 Differs From Native IGF-1

Two structural modifications define the molecule:

• Long N-terminus. A 13 amino acid extension (MFPAMPLLSLFVN) is added to the N-terminus of mature IGF-1, increasing the total length from 70 to 83 residues. This extension sterically hinders IGFBP contact and improves expression yields in E. coli.
• Arg³ substitution. Glutamate at position 3 of the mature IGF-1 sequence is replaced with arginine. Position 3 sits inside the primary IGFBP binding pocket, and this single substitution is the dominant driver of the reduced binding-protein affinity.

Together these changes drop affinity for IGFBP-3 (the dominant circulating IGF carrier) from a K_d of roughly 0.1 to 0.5 nM down to roughly 60 to 100 nM — on the order of a 600-fold reduction. Affinity at the IGF-1 receptor itself is essentially preserved, although some sources describe a modest decrease that is more than offset by the gain in free, bioactive ligand. The net result in animal studies is a peptide that is approximately three times more potent than native IGF-1 on a molar basis when delivered systemically.

The plasma kinetic difference matters clinically. Native IGF-1 cleared without its binding proteins has a half-life under 15 minutes, which is why mecasermin must be dosed twice daily and produces a sharp post-injection hypoglycemic risk. LR3 IGF-1, because it escapes IGFBP sequestration but is also cleared by the same mechanisms, paradoxically circulates as bioactive free hormone for far longer. Bastian and colleagues (PMID 7693845) showed in pregnant rats that radiolabeled LR3 IGF-1 reached different tissue distribution patterns and a substantially longer plasma half-life than the native peptide.

Mechanism of Action

IGF-1 LR3 binds and activates the type 1 IGF receptor (IGF-1R), a tyrosine kinase receptor structurally related to the insulin receptor. Receptor activation triggers two main intracellular pathways:

• PI3K / Akt / mTOR. The dominant anabolic axis. Akt activation suppresses FoxO transcription factors (reducing protein breakdown), activates mTORC1 (increasing protein synthesis), and stimulates GLUT4 translocation (increasing glucose uptake in muscle and adipose).
• Ras / Raf / MAPK. Mitogenic signaling driving cell proliferation and hyperplasia — the pathway most relevant to the cancer-promotion concerns.

The IGF-1R is roughly 60 percent homologous to the insulin receptor in its tyrosine kinase domain and the two receptors form hybrid heterodimers in many tissues. IGF-1 LR3 has modest cross-reactivity at the insulin receptor itself, which is the mechanism behind its hypoglycemic effect at higher doses.

The downstream physiologic consequences described in animal studies are predictable from the receptor biology: increased skeletal muscle protein synthesis, satellite cell activation (the cellular basis for “hyperplasia” claims), increased visceral organ mass, improved peripheral glucose uptake, and increased fatty acid oxidation. In suckling rats, systemic infusion of LR3 IGF-1 disproportionately enlarges the spleen, kidney, and gut compared with native IGF-1 at equimolar doses (PMID 9124573). These visceral organ findings are the most important caution flag in extrapolating to long-term human use.

Dosing Patterns Reported in Non-Medical Use

There are no human dosing protocols in any peer-reviewed clinical trial for IGF-1 LR3. All dosing information comes from non-medical user reports and bodybuilding forum tradition. We report it here for harm-reduction transparency, not as endorsement. Common reported daily doses are 20 to 100 mcg subcutaneously, with the great majority of users settling at 40 to 50 mcg.

• Conservative starter: 20 mcg once daily, taken on an empty stomach in the morning, for 7 to 10 days to assess tolerance and hypoglycemia risk
• Standard reported dose: 40 to 50 mcg once daily, often timed pre- or immediately post-workout
• Higher protocols: 80 to 100 mcg once daily, sometimes split into two doses; these protocols substantially raise the side-effect profile and are not endorsed by any clinician
• Cycle length: Most user protocols run 4 to 6 weeks on with at least 4 weeks off, reflecting concern about IGF-1R desensitization and theoretical safety

The biological rationale for short cycles is partly receptor-level (chronic IGF-1R stimulation downregulates the receptor in vitro) and partly a hedge against the cumulative concerns about organ growth and cancer promotion that come up later in this guide. There is no animal or human data establishing a “safe” cycle length for cosmetic use.

One important pharmacologic note: because of the ~20-hour half-life, IGF-1 LR3 produces a sustained elevation in IGF-1R signaling rather than the brief pulse of native IGF-1. Native IGF-1 is delivered to tissues in physiologic pulses against a background of IGFBP buffering; LR3 IGF-1 produces a continuous, unbuffered exposure. This is the opposite of how the endocrine system is set up to handle this signal, and it is the central reason why long-term safety cannot be inferred from short-term tolerability.

Reconstitution Math

IGF-1 LR3 is shipped as a lyophilized white powder, almost always in 1 mg vials. It is reconstituted with bacteriostatic water (preferred for any vial that will be used over multiple days) or sterile water for single-day use. Bacteriostatic water contains 0.9 percent benzyl alcohol as a preservative.

Standard reconstitution: 1 mg vial plus 1 mL bacteriostatic water yields 1 mg/mL, or 1000 mcg/mL.

• 20 mcg dose = 0.02 mL = 2 units on a U-100 insulin syringe
• 40 mcg dose = 0.04 mL = 4 units
• 50 mcg dose = 0.05 mL = 5 units
• 80 mcg dose = 0.08 mL = 8 units
• 100 mcg dose = 0.10 mL = 10 units

An alternative dilution is 1 mg vial plus 2 mL bacteriostatic water, which yields 0.5 mg/mL (500 mcg/mL). In that case 50 mcg = 0.10 mL = 10 units on the same syringe. Either approach is fine; the 1 mL dilution simply lets each tick on the syringe correspond to 10 mcg, which is easy to dose. The peptide calculator will compute units for any vial size and water volume.

Add the water slowly down the side of the vial, do not aim the stream directly at the lyophilized cake (this can denature the peptide), and swirl gently rather than shaking. Reconstituted IGF-1 LR3 should be refrigerated at 2 to 8 °C and used within roughly 14 days when made up in bacteriostatic water. Some users assume the longer 30-day window that applies to less fragile peptides; LR3 IGF-1 is more thermally labile than sermorelin or BPC-157 and degrades faster once in solution.

Pre- and Post-Workout Timing

The two most common timing strategies in non-medical use are:

• Pre-workout (30 to 45 minutes before lifting). The rationale is to have peak free IGF-1R signaling during the mechanical load that activates satellite cells. There is no human data confirming this matters for hypertrophy, but it is the dominant pattern in forum protocols.
• Immediately post-workout. The rationale is to stack IGF-1R signaling with the post-exercise window of elevated mTOR activity from mechanical and nutrient signaling. This is the timing pattern endorsed by some IGF-1 user surveys.

Because LR3 IGF-1 has a 20-hour half-life, the practical difference between pre- and post-workout timing is small — the molecule is at functionally similar plasma concentrations within an hour either way. The more important variable is consistency (daily dose at roughly the same time) and avoiding combining the injection with a large carbohydrate or insulin load, which can stack hypoglycemic risk.

Some users administer LR3 IGF-1 in a fasted state to avoid insulin-IGF additive hypoglycemia. Others administer it with a moderate protein and carbohydrate meal specifically to blunt that risk. Both strategies appear in the forum literature; neither has clinical trial support.

What the Published Evidence Actually Shows

The peer-reviewed literature on LR3 IGF-1 is almost entirely preclinical — primarily rats, sheep, pigs, and isolated cell systems — with cell-culture pharmacology comprising most of the rest. There are no randomized controlled trials of LR3 IGF-1 in humans for any indication. The most directly relevant studies are:

Lord et al. (PMID 7514204) characterized the dramatically reduced association of LR3 IGF-1 and other IGF-1 variants with plasma binding proteins across rat, sheep, pig, human, and chicken serum. This paper is the foundational reference for the “600-fold lower IGFBP affinity” figure cited throughout this guide.

Conlon et al. (PMID 7561636) infused LR3 IGF-1 systemically in guinea pigs and documented stimulated organ growth alongside reductions in endogenous IGF-1, IGF-2, and IGFBP concentrations — an early demonstration of the negative-feedback effects of supraphysiologic IGF-1R signaling.

Bastian et al. (PMID 7693845) followed radiolabeled LR3 IGF-1 versus native IGF-1 in pregnant rats and quantified the substantially longer plasma clearance and altered tissue distribution that became the headline pharmacokinetic finding for the molecule.

Steeb et al. (PMID 9124573) infused LR3 IGF-1 into suckling rats and demonstrated disproportionate visceral organ growth, particularly in the gut and spleen, compared with native IGF-1 at matched doses. This study is the most-cited reference for the “organomegaly” concern at supraphysiologic IGF-1R agonism.

Renehan et al. (PMID 15110491) is the landmark Lancet meta-regression of circulating IGF-1 and cancer risk. Higher endogenous IGF-1 was associated with increased risk of prostate, premenopausal breast, and colorectal cancer in observational cohorts. The data is for endogenous IGF-1, not for exogenous LR3, but it is the strongest reason for caution about pushing IGF-1R signaling supraphysiologically over months.

Honest summary: LR3 IGF-1 does what the receptor biology predicts — it drives skeletal muscle protein synthesis, increases organ mass, and lowers blood glucose — in rodent and large-animal models. There is no human trial confirming any of the body-composition effects routinely claimed in non-medical use, and there is no human safety database. The molecule is a research reagent, not a drug.

Safety Profile

Three categories of risk dominate the safety conversation around IGF-1 LR3. Two of them are well-documented from animal data and from the closely related mecasermin clinical experience. The third is theoretical but biologically plausible and well-supported by epidemiology.

Hypoglycemia

This is the most immediate, real-time risk. IGF-1 LR3 has measurable affinity at the insulin receptor and lowers blood glucose at higher doses. The mecasermin label (recombinant native IGF-1) lists hypoglycemia as a boxed-style precaution and requires patients to consume a meal or snack within 20 minutes of every injection. By extension, the longer half-life of LR3 IGF-1 produces a prolonged, lower-grade glucose-lowering effect throughout the day. Symptoms include sweating, shakiness, hunger, headache, palpitations, blurred vision, and confusion. Severe hypoglycemia can produce seizures or loss of consciousness. Users who stack LR3 IGF-1 with insulin, sulfonylureas, or hard fasted training are at compounded risk. The full FDA Increlex prescribing information includes detailed hypoglycemia monitoring guidance and is the closest existing analog (Increlex label, FDA).

Organ growth

The Steeb and Conlon rodent studies cited above documented disproportionate growth of the gut, spleen, kidney, and liver under chronic LR3 IGF-1 infusion. Acromegaly — the human disease caused by chronic growth hormone and IGF-1 excess from a pituitary adenoma — produces the same pattern (cardiomegaly, organomegaly, soft-tissue hypertrophy, jaw and hand growth) and is associated with reduced life expectancy. There is no published case series of acromegaly-like organ growth from short-course recreational LR3 IGF-1 use, but the biological pathway is direct and well-established.

Cancer promotion

This is the theoretical concern that is hardest to quantify but most consequential. Higher circulating endogenous IGF-1 is consistently associated with increased risk of prostate, premenopausal breast, and colorectal cancer in large observational cohorts (Renehan 2004, PMID 15110491). The IGF-1R is overexpressed or constitutively active in many human cancers, and pharmaceutical companies have spent more than a decade developing IGF-1R antagonist antibodies for oncology — the opposite of what LR3 IGF-1 does. There is no evidence that short-course recreational LR3 IGF-1 measurably raises lifetime cancer incidence. There is also no evidence that it does not. Patients with personal or family history of prostate, breast, colorectal, or any IGF-1R-driven malignancy should not use this peptide.

Other reported effects

• Local injection site irritation, redness, lipohypertrophy at the injection site over time
• Headache, light-headedness, fatigue (often related to subclinical hypoglycemia)
• Edema and water retention at higher doses
• Joint and muscle aches that resemble mild acromegaly symptoms in long users
• Hypothetical tonsillar / lymphoid hypertrophy from IGF-1R agonism on lymphoid tissue (described with mecasermin)
• Allergic reactions including anaphylaxis have been reported with mecasermin and are plausible with LR3

Anyone using LR3 IGF-1 outside a research setting should at minimum check a fasting glucose and A1c at baseline and every 4 to 6 weeks, and stop immediately for any persistent visual changes, unusual headaches, or new lumps or swelling.

Drug interactions

IGF-1 LR3 has not been evaluated in any formal pharmacokinetic drug-drug interaction trial in humans. As a modified IGF-1 analog with reduced binding-protein affinity, it produces potent systemic anabolic and hypoglycemic signaling rather than acting on hepatic CYP enzymes, so the dominant concern is pharmacodynamic rather than metabolic interaction. Overlap with glucose-lowering, growth hormone, and insulin-pathway drugs is mechanistically expected. Always consult a prescriber before combining IGF-1 LR3 with insulin, sulfonylureas, GLP-1 agonists, or growth hormone.

Cycle Lengths

Cycling summary: Recommended; 4-6 weeks on, 4+ weeks off. Receptor downregulation and hypoglycemia concern.

The typical cycle pattern for IGF-1 LR3 is 5 weeks on, 4 weeks off. Users often log time-off cycles alongside on-cycles to track receptor sensitivity, biomarker recovery, and any rebound effects. The off-cycle is not a period of "washout only" but an active reset window worth using for a lab draw.

Lab Monitoring

IGF-1 LR3 is a growth hormone axis agent, so lab monitoring should track both the intended IGF-1 response and class-effect risks on glucose regulation and cardiovascular markers. IGF-1 is the primary efficacy biomarker.

Baseline (before starting): IGF-1 (age-adjusted reference range), fasting glucose, HbA1c, lipid panel, comprehensive metabolic panel (CMP), prolactin, morning cortisol, TSH, and sex hormones if hormone optimization is part of the goal. Optional: fasting insulin for insulin-sensitivity baseline.

During use: IGF-1 every 6-8 weeks with a target of upper-quartile of age-adjusted reference range, not supraphysiologic. Fasting glucose and HbA1c every 3 months (GH-axis peptides can impair insulin sensitivity as a class effect). Lipid panel and CMP every 6 months. Prolactin only if symptoms suggest.

What to flag to a physician: IGF-1 rising above the age-adjusted 75th percentile, fasting glucose trending upward, water retention or edema, persistent joint pain, and new numbness or tingling (carpal tunnel is a documented GH-excess symptom).

For the full class-wide monitoring framework and a plain-language comparison of DTC lab services for peptide users, see the Peptide Lab Testing pillar guide.

Storage & Travel

Storage

Lyophilized powder: Freezer -20°C (-4°F) long-term; freeze OK lyophilized; protect from light.

Reconstituted: Refrigerate 2-8°C (36-46°F); use within 28 days in BAC water or 0.1% acetic acid; do not freeze. Never freeze a reconstituted vial, since freeze-thaw cycles damage peptide bonds and reduce potency.

Travel

Domestic flights: pack reconstituted vials in an insulated cooler with reusable ice packs. The TSA 3-1-1 rule limits liquids to 100 mL per container in carry-on; a 3-5 mL peptide vial passes with room to spare. Keep pharmacy or vendor documentation visible for TSA questions. Lyophilized powder in original sealed vial does not require cooling for short trips.

International travel: IGF-1 LR3 is a research peptide in most jurisdictions with varying import restrictions — check the destination country’s rules before travel. Carry a physician’s letter if the peptide was prescribed by a compounding-focused clinician.

Road trips: keep the cooler in the cabin, not the trunk, during summer. Hotel mini-fridges vary in temperature stability; an insulated bag inside the mini-fridge adds a buffer.

Emergency out-of-fridge: reconstituted IGF-1 LR3 at room temperature under 24 hours is generally still viable per USP stability guidance. Longer excursions or temperatures above 30°C compromise potency; discard and reconstitute a fresh vial.

2026 Regulatory Status

IGF-1 LR3 is not approved by the U.S. FDA for any human use. It does not appear on the FDA 503A bulk drug substances list and cannot be legally compounded for human administration in the United States (FDA 503A Bulks List). Material sold online is uniformly labeled “for research use only,” and that labeling has legal weight: human self-administration may violate state and federal law depending on jurisdiction.

Mecasermin (Increlex) — recombinant native human IGF-1, structurally different from LR3 — was FDA-approved in 2005 for the long-term treatment of growth failure in children with severe primary IGF-1 deficiency or with growth hormone gene deletion who have developed neutralizing antibodies to growth hormone. It is a specialty prescription product administered under endocrinology supervision and is not appropriate for adult cosmetic or performance use.

The World Anti-Doping Agency prohibits all IGF-1 analogs — including LR3 IGF-1, native rhIGF-1, and mechano growth factor (PEG-MGF) — under category S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) at all times, in and out of competition (WADA Prohibited List). Athletes subject to drug testing should not use this peptide.

Customs interception, payment-processor restrictions, and lab-testing variability are real-world risks for anyone purchasing research-grade peptides online. Identity, purity, and endotoxin content vary widely between vendors and even between lots from the same vendor.

FAQ

Is IGF-1 LR3 the same as Increlex?

No. Increlex (mecasermin) is recombinant native human IGF-1, structurally identical to the endogenous hormone and FDA-approved only for severe primary IGF-1 deficiency in children. IGF-1 LR3 is a modified analog with an N-terminal extension and an arginine-3 substitution that dramatically reduce IGFBP binding and extend half-life. They are different molecules with different pharmacology, different regulatory status, and different risk profiles.

How long does IGF-1 LR3 stay active in the body?

The plasma half-life is approximately 20 hours, compared with under 15 minutes for free native IGF-1. This is the consequence of escaping IGFBP sequestration but still being cleared by similar mechanisms. Practically, a single subcutaneous dose produces measurably elevated IGF-1R signaling for at least 24 hours and likely longer.

Will IGF-1 LR3 cause hyperplasia of muscle fibers?

In rodent studies, IGF-1R activation does increase satellite cell number and contributes to fiber proliferation in some models. Whether short-course exogenous LR3 IGF-1 produces meaningful, permanent hyperplasia in adult human muscle — rather than the more conventional hypertrophy from protein synthesis — has never been demonstrated in a controlled trial. The popular claim that LR3 IGF-1 “permanently adds muscle cells” significantly overstates what the human evidence supports.

Can IGF-1 LR3 cause cancer?

There is no direct evidence that short-course LR3 IGF-1 use measurably raises cancer incidence in humans, because no controlled study has been done. There is consistent epidemiologic evidence that higher endogenous IGF-1 is associated with elevated risk of prostate, premenopausal breast, and colorectal cancer (Renehan 2004). The IGF-1R is a validated oncology target. Caution is warranted, particularly for anyone with personal or family cancer history.

Why is hypoglycemia the biggest acute risk?

IGF-1 LR3 has measurable cross-reactivity at the insulin receptor and produces a sustained, low-grade glucose-lowering effect over its 20-hour half-life. Symptoms can appear hours after the injection, often mid-workout or overnight, when the user is not actively monitoring. Stacking with insulin, sulfonylureas, or aggressive fasted training compounds the risk substantially.

How is IGF-1 LR3 different from MGF or PEG-MGF?

Mechano growth factor (MGF) is a splice variant of IGF-1 (IGF-1Ec in humans) with a unique C-terminal E-domain peptide thought to act on satellite cells through a partly distinct receptor mechanism. PEG-MGF is a pegylated synthetic version of that E-domain peptide. Both are also research-only and not on the 503A bulks list. LR3 IGF-1 is the systemic, long-acting agonist of the full IGF-1R; MGF analogs are more often used (in animal work) for local muscle effects.

Can I stack IGF-1 LR3 with growth hormone or GH-releasing peptides?

This is a common pattern in non-medical use. The pharmacologic logic is that GH or GHRH analogs raise endogenous IGF-1 through hepatic synthesis while LR3 IGF-1 adds an unbuffered systemic IGF-1R signal directly. The combined effect on hypoglycemia risk, organ growth, and cancer-promotion signaling is additive at best and potentially supra-additive. No clinician supervising hormone optimization recommends this stack outside an investigational setting.

Will IGF-1 LR3 raise my serum IGF-1 lab value?

Yes, in most assays. Standard clinical IGF-1 immunoassays will pick up LR3 IGF-1 to a variable degree depending on the antibody used. Forum reports describe IGF-1 lab values rising into the supraphysiologic range during cycles. A measurably elevated IGF-1 on an off-cycle lab draw is also why this peptide cannot be hidden from a thoughtful endocrinology workup.

What labs should I run before and during use?

If you are considering this peptide despite the lack of clinical support, the minimum lab baseline that any sports-endocrinology clinician would want is: fasting glucose, hemoglobin A1c, comprehensive metabolic panel, fasting insulin, IGF-1, IGFBP-3, complete blood count, and (for men over 40) a baseline PSA. Repeat fasting glucose and A1c every 4 to 6 weeks. Stop for any persistent visual change, severe headache, new mass or swelling, or unexpected weight gain.

Is IGF-1 LR3 legal to possess?

Possession of research-grade peptides for non-human research use is generally not federally prohibited, but human self-administration of an unapproved drug is regulated at both federal and state levels, and the legal landscape shifted significantly with the FDA’s 2024 to 2026 Category 2 actions on unapproved peptides. Customs interception, payment-processor refusals, and varying state pharmacy law all apply. This guide is informational only and does not constitute legal advice.

References

• Lord AP, Bastian SE, Read LC, et al. Differences in the association of insulin-like growth factor-I (IGF-I) and IGF-I variants with rat, sheep, pig, human and chicken plasma-binding proteins. J Endocrinol. 1994;140(1):121-130. PMID 7514204.
• Bastian SE, Walton PE, Ballard FJ, Belford DA. Plasma clearance and tissue distribution of labelled insulin-like growth factor-I (IGF-I) and an analogue LR3IGF-I in pregnant rats. J Endocrinol. 1993;138(2):337-343. PMID 7693845.
• Conlon MA, Tomas FM, Owens PC, et al. Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig. J Endocrinol. 1995;146(2):247-253. PMID 7561636.
• Steeb CB, Trahair JF, Tomas FM, Read LC. Systemic infusion of IGF-I or LR(3)IGF-I stimulates visceral organ growth and proliferation of gut tissues in suckling rats. Am J Physiol. 1997;272(3 Pt 1):G375-G381. PMID 9124573.
• Renehan AG, Zwahlen M, Minder C, et al. Insulin-like growth factor (IGF)-I, IGF binding protein-3, and cancer risk: systematic review and meta-regression analysis. Lancet. 2004;363(9418):1346-1353. PMID 15110491.
• Kemp SF. Mecasermin rinfabate. Drugs Today (Barc). 2007;43(3):149-155. PMID 17380212.
• Kemp SF. Investigational agents for the treatment of growth hormone-insensitivity syndrome. Expert Opin Investig Drugs. 2006;15(4):419-428. PMID 16548790.
• U.S. Food and Drug Administration. INCRELEX (mecasermin) injection — prescribing information. accessdata.fda.gov.
• U.S. Food and Drug Administration. Bulk drug substances used in compounding under Section 503A of the FD&C Act. fda.gov.
• World Anti-Doping Agency. Prohibited List 2026 — Section S2: Peptide Hormones, Growth Factors, Related Substances and Mimetics. wada-ama.org.

Educational content only. Not medical advice. IGF-1 LR3 is not approved for human use in the United States. Consult a licensed clinician before considering any peptide protocol.