Muscle & tissue growth booster (IGF-1 LR3)
A lab-engineered version of the body's IGF-1 growth factor, designed to stay active longer and stimulate muscle and tissue growth; used only as a lab and animal research tool, not an approved drug.
- Class
- Modified recombinant IGF-1 analog (growth factor research reagent / performance-enhancement compound)
- Status
- Not approved for any human therapeutic indication in the US, EU, UK, Canada, or Australia; developed as a cell culture reagent; sold through research-chemical supply channels
- Best-supported effect
- Enhanced anabolism, gut and organ tissue growth, and sustained IGF-1 receptor activation in animal models; IGFBP-bypass mechanism well-validated preclinically
- Main caveat
- No human clinical trials of IGF-1 LR3 for any indication; the compound is mechanistically engineered to produce the sustained IGF-1 elevation pattern that large prospective cohort studies consistently associate with increased cancer risk; human safety at any dose or duration is uncharacterized
A researcher, an agent, or an algorithm wrote down the sequence and picked a target to hit.
An AI model like OpenFold3 or AlphaFold built a 3D structure and scored how well it fits the binding site.
A second contributor repeated the computation on their own hardware and the scores matched.
A chemistry service or a researcher ordered the sequence, it was manufactured, and mass spectrometry confirmed the right molecule was produced.
A binding or activity measurement confirmed that it actually does what the computer predicted — or didn't.
Snapshot
Class: Modified recombinant IGF-1 analog (growth factor research reagent / performance-enhancement compound)
Evidence tier: Animal-only evidence
Status: Not approved for any human therapeutic indication in the US, EU, UK, Canada, or Australia; developed as a cell culture reagent; sold through research-chemical supply channels
Best-supported effect: Enhanced anabolism, gut and organ tissue growth, and sustained IGF-1 receptor activation in animal models; IGFBP-bypass mechanism well-validated preclinically
Main caveat: No human clinical trials of IGF-1 LR3 for any indication; the compound is mechanistically engineered to produce the sustained IGF-1 elevation pattern that large prospective cohort studies consistently associate with increased cancer risk; human safety at any dose or duration is uncharacterized
What this is
IGF-1 LR3 (Long R3 IGF-1) is a recombinant analog of human insulin-like growth factor-1 carrying two deliberate structural modifications: an arginine-to-glutamate substitution at position 3, and a 13-amino-acid N-terminal extension derived from methionyl porcine growth hormone. Together these changes sharply reduce affinity for IGF binding proteins (IGFBPs), which are the body's primary mechanism for sequestering and regulating circulating IGF-1, and extend plasma half-life from approximately 12 minutes for native IGF-1 to roughly 20–30 hours.
The molecule was originally developed in the late 1980s and early 1990s — principally by groups including F. John Ballard and colleagues at CSIRO in Adelaide, in the context of broader IGF-1 biology research — as a cell-culture reagent: a tool to maintain IGF-1 bioactivity in serum-containing media where endogenous binding proteins would otherwise neutralize it. It was never developed for any human therapeutic indication and has never been submitted for regulatory approval anywhere.
In the 2000s, LR3 transitioned from research-reagent supply chains into bodybuilding and performance-enhancement use outside any regulatory framework. Recombinant human IGF-1 (mecasermin, Increlex) is an FDA-approved drug for severe primary IGF-1 deficiency in children, but IGF-1 LR3 is a chemically distinct analog with different pharmacokinetics and carries no regulatory equivalence to mecasermin.
The pharmacological distinction between IGF-1 LR3 and native IGF-1 is not simply potency. Native IGF-1 operates through tight, pulsatile, binding-protein-mediated cycles; LR3 is specifically engineered to defeat that regulatory system, imposing sustained, unregulated IGF-1 receptor activation for a day or more per dose. This is a fundamentally different signaling pattern — and the pattern that the cancer-risk epidemiology consistently identifies as the concern.
Evidence map
| Evidence layer | Grade | What it supports |
|---|---|---|
| Human | None | No human clinical trial data for IGF-1 LR3 identified |
| Animal | Moderate | Enhanced anabolism, lean tissue accrual, intestinal and organ tissue growth, extended pharmacokinetics and greater potency vs native IGF-1 across multiple species; one 2024 study in late-gestation growth-restricted fetal sheep found no growth benefit despite metabolic shift — a meaningful translational caution |
| In vitro | Moderate | IGF-1R binding, IGFBP-bypass mechanism validation, PI3K/Akt/mTOR and Ras/MAPK/ERK pathway activation characterized |
| Computational | None identified | No computational modeling or docking data attached |
| Mechanism | Strong | IGF-1R signaling cascade is among the best-characterized growth factor pathways in biology; structural basis for IGFBP-bypass is established; epidemiologic associations between elevated endogenous circulating IGF-1 and multiple cancer types are consistently replicated across large prospective cohort studies — this is human observational evidence for the biomarker, not exogenous LR3 efficacy trials |
Evidence concentration note: The preclinical evidence base is distributed across organ-growth, pharmacokinetic, and anabolic endpoints from multiple labs. The cancer-risk signal comes from independent large epidemiological cohorts unconnected to LR3 development.
Claim check
| Claim | Verdict | Evidence layer | Confidence |
|---|---|---|---|
| Produces muscle growth and anabolic tissue effects via IGF-1R activation | Supported (animal / preclinical) | Animal | Medium — extensive preclinical support across species; no controlled human efficacy data; 2024 animal study shows growth response is not guaranteed even in high-need contexts |
| Chronic elevated circulating IGF-1 is associated with increased cancer risk | Supported (human observational) | Human | High — large replicated prospective cohort studies for prostate, breast, colorectal, and lung cancers; this is an endogenous IGF-1 biomarker association, not an LR3 intervention trial; LR3-specific cancer risk in humans is unstudied; observational association, causality from endogenous levels established, exogenous LR3 causal pathway not directly studied |
| Causes acute hypoglycemia via insulin-receptor cross-reactivity | Supported (animal / preclinical) | Animal | Medium — confirmed in multi-species animal models; community-reported in human performance use; no formal human dose-response or safety study |
| Produces tissue and organ overgrowth with sustained use | Partially supported (animal / preclinical) | Animal | Medium — intestinal and organ tissue growth seen in preclinical models with prolonged IGF analog exposure; acromegaly-like effects mechanistically expected; formal human documentation at performance-use doses absent |
| "Safer than IGF-1 DES or native IGF-1" for performance use | Contradicted / not supported | None | High — extended half-life produces sustained supraphysiological exposure rather than brief spikes; sustained unregulated IGF-1R activation is pharmacologically distinct from pulsatile native signaling and is precisely what the cancer-risk epidemiology identifies as the concern; this framing is not supported by the pharmacology |
| Short cycles eliminate cancer risk | Weak / not established | None | High — no prospective tracking of performance-use populations for cancer endpoints; cancer latency is measured in decades; community users are not systematically monitored; the epidemiological concern is probabilistic at population level and cannot be resolved by cycle-length conventions not derived from human evidence |
| Equivalent to or covered by FDA-approved mecasermin (Increlex) | Contradicted | Human | High — mecasermin is recombinant native IGF-1 approved for a narrow pediatric indication under strict monitoring; LR3 is a chemically distinct analog with different pharmacokinetics; never submitted for any regulatory approval; no regulatory or clinical equivalence |
Experimental exposure
This section reports exposure used in animal experiments. It does not establish human dosing.
| Context | System | Experimental exposure | Duration | Endpoint | Limitation |
|---|---|---|---|---|---|
| Anabolism studies | Normal female rats; neonatal pigs; multiple species | Species- and study-specific doses; individual regimens not separately extracted in this card | Acute to multi-week; study-specific | Lean tissue accrual, organ growth, IGF-1R activation | No human translation established |
| Pharmacokinetics | Rats, marmosets | Comparative infusion and injection protocols; doses not individually extracted | Acute | Plasma clearance, IGFBP displacement, half-life comparison with native IGF-1 | Animal pharmacokinetics; human half-life estimate (20–30 hours) is extrapolated, not from a controlled human PK study |
| Hypoglycaemia model | Pigs and marmoset monkeys | IGF-1 LR3 vs native IGF-1; doses not individually extracted | Short-term | Hypoglycaemic potency and duration vs native IGF-1 | Multi-species; directly relevant to safety concern; no human dose-finding |
| Fetal growth-restriction model | Fetal sheep (late-gestation) | Study-specific infusion dose; one-week course | 1 week | Fetal growth, amino-acid handling, insulin secretion markers | Negative translational result: metabolic markers shifted but growth endpoint not improved; developmental and species factors limit translation to adult performance use |
| Gastrointestinal tissue model | Adult rats | Prolonged IGF-peptide administration; doses not individually extracted | Prolonged course | Gastrointestinal tissue weight and growth | Preclinical; gut-growth findings are the preclinical basis for the organomegaly concern |
Preclinical safety signals
| Signal | System | Notes |
|---|---|---|
| Acute hypoglycemia | Animal (pigs, marmosets); mechanistic | IGF-1 LR3 produces more potent and prolonged hypoglycaemic action than native IGF-1 in multi-species preclinical studies; mechanistic basis is insulin-receptor cross-reactivity at sufficient concentrations; community-use reports of hypoglycaemia symptoms hours after dosing are consistent with this pharmacology |
| Organ and gut tissue growth (organomegaly) | Animal (rat, pig) | Prolonged IGF-peptide administration in preclinical models associated with gastrointestinal and organ tissue growth; acromegaly-like effects are mechanistically expected from sustained supraphysiological IGF-1R activation |
| Suppression of endogenous IGF-1, GH, and IGFBP-3 | Animal (pigs) | Long [R3] IGF-1 reduced plasma GH, IGFBP-3, and endogenous IGF-1 in preclinical study; endocrine-axis feedback expected from exogenous IGF-1R agonism; human axis effects not characterized |
| Cancer risk from sustained IGF-1 elevation | Human epidemiology (observational, endogenous IGF-1) | Renehan et al. 2004 Lancet meta-analysis establishes replicated association between elevated circulating IGF-1 and multiple cancer types across large cohorts; Chan et al. 1998 prospective study links IGF-1 to prostate cancer; Guevara-Aguirre et al. 2011 Laron syndrome data shows reduced IGF-1 signaling associates with dramatically lower cancer incidence. These data concern endogenous IGF-1 in population cohorts, not exogenous LR3 administration. LR3 is engineered to produce sustained supraphysiological free IGF-1R activation — matching the exposure pattern the epidemiology characterizes |
| Cancer immune evasion mechanism (preclinical, 2025) | Preclinical / mechanistic | 2025 source describes IGF-1 signaling promoting FOXP3+ Treg function and M2 macrophage polarization in prostate cancer models, extending the cancer-risk mechanism to immune surveillance suppression beyond direct proliferative effects |
| Long-term human safety | Not established | No systematic human safety data at any dose or duration; no pharmacovigilance infrastructure for LR3 users exists |
| Research-chemical supply quality | Quality context | Purity, correct peptide identity, and endotoxin content of commercially sold LR3 are not subject to pharmaceutical-grade QA; contamination or misidentification documented in peptide market studies |
Regulatory status
| Region / body | Status | Notes |
|---|---|---|
| US (FDA) | Not approved | No approved indication for any human use; LR3 developed as cell-culture reagent, not therapeutic; sold through research-chemical channels labeled "not for human use"; distribution for human consumption is not authorized; selling for human use constitutes an unapproved drug violation under the FD&C Act |
| EU | Not approved | Per available sources, no approval in the EU; independent verification of current EU status not performed in this card |
| UK | Not approved | Per available sources, not approved in the UK |
| Canada | Not approved | Per available sources, not approved in Canada |
| Australia (TGA) | Schedule 4 prescription-only (per available sources) | Per available sources, TGA treats LR3 as Schedule 4 and has pursued enforcement against unauthorized sellers; importation for personal use reported as restricted |
| WADA | Prohibited at all times (per available sources) | Per available sources, prohibited under S2 (peptide hormones, growth factors, related substances, and mimetics), which explicitly covers IGF-1 and its analogs; prohibited in and out of competition; detection windows continue to extend with improved mass-spectrometry methods; per available sources status — current list status not independently refreshed in this card |
| Compounding | Not modeled | Compounding status not assessed in this card |
| Mecasermin (Increlex) note | Distinct; not equivalent | Recombinant human IGF-1 (mecasermin) is FDA-approved for severe primary IGF-1 deficiency in children under strict monitoring; LR3 is a chemically distinct analog and the approval does not extend to it |
Mechanism
IGF-1 LR3 acts as an agonist at the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase. Its binding affinity for IGF-1R is similar to native IGF-1, but dramatically reduced affinity for IGF binding proteins — particularly IGFBP-3 and IGFBP-5 — means the peptide circulates predominantly as free, biologically active molecules rather than in the sequestered, bound form that limits native IGF-1's tissue exposure and duration.
IGF-1R activation initiates two primary downstream signaling cascades. The PI3K/Akt/mTOR pathway drives protein synthesis, cellular hypertrophy, and satellite cell activation in muscle tissue. The Ras/MAPK/ERK pathway promotes cell proliferation. Both pathways are mitogenic: they support growth of target tissues and, at sustained supraphysiological levels, constitute the mechanistic basis underlying the cancer-risk concern.
The 20–30 hour half-life produces prolonged, non-pulsatile mTOR activation and satellite cell stimulation, which has been proposed as a mechanism for potential muscle hyperplasia (new fiber formation) in addition to hypertrophy. This has been characterized in animal and cell systems. The body's normal IGF-1 regulation depends on binding proteins to enforce pulsatile, bounded signaling. LR3 is specifically engineered to circumvent this regulation.
At sufficient concentrations, IGF-1 cross-activates insulin receptors, producing glucose-lowering effects. The extended half-life of LR3 prolongs this glucose-lowering action compared to native IGF-1, producing delayed-onset hypoglycemia lasting hours.
The same PI3K/Akt and MAPK/ERK pathways activated for anabolism are implicated in cancer cell proliferation. Recent work has additionally identified IGF-1 signaling as a driver of tumor immune evasion through FOXP3+ regulatory T-cell function and M2 macrophage polarization — extending the risk mechanism beyond direct proliferative effects.
Chemistry
| Field | Value |
|---|---|
| Names | IGF-1 LR3; Long R3 IGF-1; Long Arginine 3 IGF-1 |
| Structure | 13-residue N-terminal extension (MFPAMPLSSLFVN — sequence truncated in source at this point) + native 70-residue IGF-1 sequence with Glu at position 3 |
| Amino-acid count | 83 (13 N-terminal extension + 70 native IGF-1 residues) |
| Key modification 1 | Arginine-to-glutamate substitution at position 3 — disrupts IGFBP binding epitope |
| Key modification 2 | 13-amino-acid N-terminal extension — further reduces IGFBP affinity; extends half-life |
| Topology | Linear |
| Molecular formula | C400H625N111O115S9 |
| Molecular weight | ~9,100 Da |
| CAS | 946870-92-4 |
| Half-life (vs native IGF-1) | ~20–30 hours (vs ~12 minutes for native IGF-1); estimate from animal studies; human PK not formally studied |
| Origin | Recombinant; originally developed as cell-culture reagent; no approved pharmaceutical indication ever pursued |
| Sequence confidence | Needs review — N-terminal extension sequence is truncated in source (source text cuts off mid-residue); full canonical sequence not separately confirmed in this card |
Open questions
- Human clinical efficacy for any indication: No controlled human trial of IGF-1 LR3 has been conducted. Whether the preclinical anabolic effects translate to humans at any dose remains unestablished.
- Cancer risk at performance-use doses and durations: Epidemiological evidence links elevated circulating IGF-1 to several cancers, but no study has characterized the specific dose-response or cumulative-exposure cancer risk attributable to repeated episodic supraphysiological LR3 use in adults. Cancer latency in relevant cohorts is measured in decades; the community-use period is too short and unsurveilled to provide meaningful signal.
- Dose-response for anabolism versus adverse effects: Community dosing (20–100 mcg) is not anchored in any human dose-ranging study. Minimum effective dose, maximum tolerated dose, and the range at which hypoglycemia or organomegaly risks become clinically meaningful in humans are unknown.
- Organomegaly thresholds in humans: Preclinical work documents gut, heart, and kidney growth with chronic IGF-analogue administration. Human thresholds for clinically meaningful organ changes have not been characterized.
- Human pharmacokinetics: The 20–30 hour half-life estimate is derived from animal data and extrapolation; controlled human PK data for LR3 do not exist.
- Negative translational result implications: A 2024 study in late-gestation growth-restricted fetal sheep found that LR3 shifted amino-acid handling but did not improve growth. Whether and how this negative result in a stressed developmental model relates to healthy adult anabolic use is uncharacterized.
- Research-chemical supply integrity: Purity, correct peptide identity, and endotoxin content of commercially sold LR3 are not subject to pharmaceutical-grade QA. Supply quality is an open safety variable independent of the underlying pharmacology.
- Injection-site tissue changes: Repeated subcutaneous or intramuscular injection is anecdotally associated with local tissue changes; no systematic imaging or histologic study in humans has been conducted.
- Immune surveillance implications: 2025 preclinical work links IGF-1 signaling to cancer immune evasion via Treg and macrophage polarization mechanisms. How this intersects with subclinical neoplastic risk in LR3 users is uncharacterized.
Research directions for this peptide, selected from the current sources — hypotheses you can explore and model. None of it is proven yet; tap any one to see the full thinking.
When patients take steroids, their bodies produce proteins that trap natural growth factor. Could this engineered peptide slip past that trap and keep muscles from wasting away?
If true, this could give people on long-term steroid therapy, such as transplant recipients or those with autoimmune disease, a way to prevent the severe muscle loss that currently has no approved treatment. It would mean they could stay on the steroids they need without the disabling weakness that often forces dose cuts.
Is the N-terminal extension just a bulky piece that physically blocks binding proteins from reaching IGF-1, rather than actively competing with them?
If true, the extension would be a modular plug-in: you could theoretically attach a similar-sized structured piece to other growth factors to give them the same evasion superpower. That would turn a single-molecule trick into a general design rule for making long-acting growth factors.
Could the very modification that makes this peptide last longer in blood also make it bind its target receptor more weakly?
If true, this would explain why animals need such high doses to see an effect, and it would point drug developers toward trimming or reshaping the N-terminal extension rather than chasing even longer half-life. That could lead to a next-generation version that keeps the IGF-1R binding strength of natural IGF-1 while still evading the proteins that normally trap it.
Might this peptide's unusually long stay in the body allow it to reach and remodel tendon tissue in ways that normal growth factor cannot?
If true, this could offer a new approach for athletes and older adults with chronic tendon injuries, where current treatments are limited to rest, physical therapy, or surgery. A peptide that actively drives tendon matrix repair would fill a genuine gap in sports and orthopedic medicine.
Might the same changes that let this peptide evade binding proteins also make it hit the insulin receptor, causing unexpected organ growth?
If this cross-reactivity is real, it would explain why animals develop unusual gut and organ enlargement, and it would warn developers that human use could carry hypoglycemia and abnormal tissue growth risks that native IGF-1 does not. A more selective next-generation analog could then be designed to keep the IGFBP evasion while restoring insulin receptor discrimination.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.26879972219467163 | boltz-2 |
| ranking score | 0.4936368465423584 | boltz-2 |
▸3-letter notation
▸recipeboltz-2 2.2.1
| parameter | value |
|---|---|
| model | boltz-2 2.2.1 |
| weights | — |
| hardware | vast_v100_32gb |
| mlx version | — |
| python | — |
| random seed | 1 |
| msa strategy | colabfold_local |
| runtime | — |
| predicted by | — |
| predicted at | 2026-05-22 |
▸citationbibtex
@peptide{pep10828,
sequence = {MFPAMPLLGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA},
target = {igf-1r},
author = {peptidemodel},
year = {2026},
status = {bioassayed}
}