--- title: "IGF-1 LR3: what sources report" url: https://humanpeptides.fyi/peptides/igf-1-lr3 site: humanpeptides.fyi last_reviewed: 2026-10-11 --- # IGF-1 LR3 > humanpeptides.fyi makes no claims of its own. Every statement below reports what a cited source says, with its link. Not medical advice. IGF-1 LR3: Engineered long-acting analogue of insulin-like growth factor-1 with reduced binding to IGF-binding proteins, making it more potent in cell/animal studies. The sources cited here most often discuss it for: Muscle growth, no human data; Growth in catabolic rats; Native IGF-1 is an approved drug. Evidence label: Preclinical. ## At a glance - **Type:** Peptide - **Family:** Growth Hormone Axis - **Evidence label:** Preclinical (2 of 5) - **Regulatory status:** Not FDA-approved for human use and sold as a research chemical; the World Anti-Doping Agency bans IGF-1 variants in competitive sport. - **Goals discussed:** Muscle & Tone, Hormones & Fertility - **Also called:** Long R3 Insulin-like Growth Factor-1, insulin-like growth factor-1, long [Arg3], IGF-1LR3, LR3, igflr3, Long R3 IGF-1 - **Last reviewed:** 2026-10-11 ## What is IGF-1 LR3? - Engineered long-acting analogue of insulin-like growth factor-1 with reduced binding to IGF-binding proteins, making it more potent in cell/animal studies; not approved for human use (the approved IGF-1 drug is mecasermin/Increlex); prohibited in sport. Sources: , **Regulatory status:** Not FDA-approved for human use and sold as a research chemical; the World Anti-Doping Agency bans IGF-1 variants in competitive sport. Source: ## What is IGF-1 LR3 researched for? ### 1. Muscle growth, no human data - Muscle growth/'pumps' are the main use, but there is no human muscle-growth evidence; users report fullness/pumps and sometimes better recovery, lasting gains inconsistent (anecdotal/Reddit) Sources: , , - Goals: [Muscle & Tone](https://humanpeptides.fyi/objectives/muscle) ### 2. Growth in catabolic rats - Growth restoration in diabetic/catabolic rats without all insulin-like effects (animal), but reduced growth and feed intake in pigs (animal, inconsistent) Sources: , - Goals: [Muscle & Tone](https://humanpeptides.fyi/objectives/muscle) ### 3. Native IGF-1 is an approved drug - Native IGF-1 (mecasermin) is FDA-approved for severe primary IGF-1 deficiency in children - shows IGF-1's growth-promoting effects but does not validate LR3 (FDA label) Sources: - Goals: [Hormones & Fertility](https://humanpeptides.fyi/objectives/hormones) ## What do researchers and users say about IGF-1 LR3? > "At the opposite end, CJC-1295 without DAC, PEG-MGF, and IGF-1 LR3 (tier D) have no peer-reviewed human studies and are supported only by preclinical extrapolation and grey-literature user narratives." > > Dominikowski A, et al., The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration (Frontiers in Endocrinology, 2026). Context: Narrative review grading the evidence for growth hormone and IGF-1 axis peptides from tier A (approved, RCT-backed) to tier D. > "This underscores that anabolic signalling and body recomposition do not necessarily translate into clinically meaningful physical performance gains" > > Dominikowski A, et al., The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis (Frontiers in Endocrinology, 2026). Context: Comment on trials of native IGF-1 in patients with neuromuscular disorders, where lean mass rose without clear functional gains. > "Lr3 is a serious gym pump after about 2 weeks but those gains aren't permanent." > > Anonymous user, r/PeptideGuide, IGF-1LR3 Experiences/Advice. Context: Self-report from a long-term user in a forum thread; uncontrolled anecdote. ## What side effects of IGF-1 LR3 are reported? - Hypoglycemia (shakiness, sweating, tunnel vision), especially fasted (anecdotal + mecasermin label warns of severe hypoglycemia) Sources: , - Possible tumor growth (animal; mecasermin contraindicated with malignancy) Sources: , - Unregulated product quality Sources: - Acromegaly-like changes (enlarged jaw, hands, feet or internal organs) and concern about heart enlargement with prolonged high IGF-1 exposure. (theoretical (community guide)) Sources: - Joint pain, water retention, headaches and nausea. (anecdotal (community guide)) Sources: - Possible suppression of the body's own growth hormone and IGF-1 production, and receptor desensitization with prolonged use. (theoretical (community guide)) Sources: - Feeling drained or lethargic, which users attribute to drops in blood sugar, and warnings that very high IGF-1 can quickly enlarge the waist. (anecdotal) Sources: - Raised resting heart rate reported by some users. (anecdotal) Sources: ## What do peptide guides say about IGF-1 LR3? - **PepEdHub:** PepEdHub describes IGF-1 LR3 as IGF-1 with an arginine swap at position 3 plus a 13-amino-acid extension, which it says reduces binding-protein capture and stretches half-life to roughly a day. - **Seek Peptides:** Seek Peptides calls low blood sugar the most common and immediately dangerous effect, and warns of acromegaly-like enlargement of jaw, hands, feet and organs with prolonged high exposure. - **Frontiers in Endocrinology:** A 2026 review notes off-label reports center on low-blood-sugar symptoms and treats cancer risk as theoretical but clinically relevant, given links between high circulating IGF-1 and several cancers. ## What does the research say, system by system? ### Body & tissues - Theoretical organ/tissue overgrowth with IGF-axis stimulation Sources: ### Hormones & physiology - Insulin-like glucose lowering (hypoglycemia risk); alters GH/IGF axis components in pigs (animal) Sources: , ### Cells & mitochondria - Reduced IGFBP binding gives greater cellular activity in culture (in vitro) Sources: ### Weight & metabolism - No human data found; glucose-lowering effect Sources: ### Muscle - No human data; anecdotal pumps/fullness and recovery Sources: ### Also notable - Review of GH-IGF1 performance peptides highlights gap between clinical evidence and self-administration Sources: ## How strong is the evidence for IGF-1 LR3? **Preclinical** (2 of 5). In vitro + inconsistent animal data + anecdotal; no human trials _Mostly cell and animal studies. Human effects unknown._ ## Street names and stacks - Street names: [LR3](https://humanpeptides.fyi/street-names#nick-lr3) ## Questions about IGF-1 LR3 ### What is IGF-1 LR3? Engineered long-acting analogue of insulin-like growth factor-1 with reduced binding to IGF-binding proteins, making it more potent in cell/animal studies. ### Is IGF-1 LR3 FDA-approved? Not FDA-approved for human use and sold as a research chemical; the World Anti-Doping Agency bans IGF-1 variants in competitive sport. ### What is IGF-1 LR3 researched for? The sources cited on this page most often discuss three outcomes: Muscle growth, no human data; Growth in catabolic rats; Native IGF-1 is an approved drug. Each line above shows what the source reports and how strong that evidence is. ### What side effects of IGF-1 LR3 are reported? Reported in the cited sources: Hypoglycemia (shakiness, sweating, tunnel vision), especially fasted; Possible tumor growth; Unregulated product quality. The list is not complete, and few listed risks does not mean a compound is safe. ### How strong is the evidence for IGF-1 LR3? Evidence label: Preclinical. In vitro + inconsistent animal data + anecdotal; no human trials. ### What else is IGF-1 LR3 called? Names used for it include Long R3 Insulin-like Growth Factor-1, insulin-like growth factor-1, long [Arg3], IGF-1LR3, LR3, igflr3, Long R3 IGF-1. ### Does humanpeptides.fyi recommend IGF-1 LR3? No. humanpeptides.fyi makes no claims and no recommendations of its own. It summarizes and links to what others have published and posted. Nothing here is medical advice; talk to a licensed clinician. --- Family: [Growth Hormone Axis](https://humanpeptides.fyi/peptides?cat=gh-axis). HTML version: . Disclaimer: