IGF-1 LR3
Synthetic IGF-1 analog with N-terminal extension and arginine substitution at position 3
- Class
- Long-acting IGF-1 analog
- Half-life
- 20–30 hours
- Route
- Subcutaneous (SubQ)
- Cadence
- Daily
- Evidence
- Animal data primarily
Overview
IGF-1 LR3 is a lab-modified version of insulin-like growth factor-1 — the hormone your liver makes in response to growth hormone. Two structural tweaks (an extra 13 amino acids at one end, and swapping one amino acid for another) give it a half-life of 20–30 hours instead of minutes, and cut its binding to IGF-binding proteins by about 1000-fold. The result: far more of the peptide stays free in your blood, hitting IGF-1 receptors harder and longer than the native hormone ever could.
It's hugely popular in bodybuilding circles for one reason — direct anabolic signaling. Unlike growth-hormone secretagogues that work upstream, IGF-1 LR3 binds straight to the IGF-1 receptor on muscle cells, flipping on the PI3K/Akt/mTOR pathway (protein synthesis) and MAPK/ERK pathway (cell division). In animal models it drives both hypertrophy (bigger muscle cells) and hyperplasia (more muscle cells) — the latter being something resistance training alone doesn't reliably do. But here's the gap: there are zero published human clinical trials of IGF-1 LR3 for any indication. All the dosing protocols floating around research and bodybuilding communities are extrapolated from mecasermin (FDA-approved native IGF-1 for severe growth deficiency in kids), animal studies, and decades of anecdotal use.
The two big safety concerns are real, not hype. First, hypoglycemia — IGF-1 LR3 cross-reacts with insulin receptors and can drop blood glucose 15–25 mg/dL for the duration of that 20–30 hour half-life. People quit mid-cycle because of sweating, confusion, and crashes if they don't time carbs around the injection. Second, cancer signaling. IGF-1 receptor activation is one of the most well-studied growth pathways in tumor biology — it's pro-proliferative and anti-apoptotic. Epidemiological data link elevated circulating IGF-1 to higher risk of several cancers in human cohorts. If you have active cancer, a history of cancer, or strong family history, this compound is a hard no.
Safety considerations
A few of the safety signals worth knowing — the full list, with dosing context and what to monitor, is inside AIx Core.
- Not approved by any regulator anywhere. Sold as a research chemical — purity and actual peptide content vary wildly between sources.
- Banned by WADA at all times. Athletes subject to drug testing should not use this compound.
- Hypoglycemia is the dominant acute risk. Blood glucose can drop 15–25 mg/dL and stay low for 20+ hours. Always have fast-acting carbs (glucose tablets, juice) on hand. Injecting fasted or combining with insulin/sulfonylureas amplifies the risk.
+ 4 more safety notes inside AIx Core →
Commonly monitored
Markers and signals people track when researching IGF-1 LR3.
- Fasting blood glucose (hypoglycemia is the most common acute side effect)
- Body composition via DEXA or similar (not just scale weight — you want lean vs fat mass)
- Fasting insulin and HbA1c (chronic use can paradoxically cause insulin resistance)
- Any new lumps, masses, or changes in moles (IGF-1R signaling is mitogenic)
- Joint pain or hand/foot swelling (can signal acromegaly-like changes)
Frequently asked questions
What is IGF-1 LR3?
Synthetic IGF-1 analog with N-terminal extension and arginine substitution at position 3. IGF-1 LR3 is a lab-modified version of insulin-like growth factor-1 — the hormone your liver makes in response to growth hormone. Two structural tweaks (an extra 13 amino acids at one end, and swapping one amino acid for another) give it a half-life of 20–30 hours instead of minutes, and cut its binding to IGF-binding proteins by about 1000-fold. The result: far more of the peptide stays free in your blood, hitting IGF-1 receptors harder and longer than the native hormone ever could.
How is IGF-1 LR3 administered?
Subcutaneous (SubQ), typically daily.
What is the half-life of IGF-1 LR3?
20–30 hours — About 10× longer than native IGF-1 — supports once-daily dosing.
Is IGF-1 LR3 approved for human use?
IGF-1 LR3 is investigational — not approved by the FDA, EMA, or MHRA for human use at the time of writing.
What does the evidence show for IGF-1 LR3?
Evidence tier: Animal data primarily. No formal human clinical trial has ever evaluated IGF-1 LR3 for any therapeutic or performance endpoint (confirmed in multiple 2026 protocol sources). All dosing is extrapolated from animal work, mecasermin clinical data, and community reporting.
What is commonly monitored when researching IGF-1 LR3?
Commonly tracked markers + signals: Fasting blood glucose (hypoglycemia is the most common acute side effect), Body composition via DEXA or similar (not just scale weight — you want lean vs fat mass), Fasting insulin and HbA1c (chronic use can paradoxically cause insulin resistance), Any new lumps, masses, or changes in moles (IGF-1R signaling is mitogenic), Joint pain or hand/foot swelling (can signal acromegaly-like changes).
Related compounds
Open this in AIx Core for the full picture
Mechanism breakdown, receptor pathway diagram, full safety list, monitored items, source citations, and one-tap add-to-protocol. Free with any account.