IGF-1 LR3
Long R3 IGF-1 · LR3
Long-acting IGF-1 analog engineered to resist binding proteins; muscle-growth research compound.
Key takeaways
- Engineered IGF-1 analog (Arg3 + N-terminal extension) that evades binding proteins.
- Estimated 12-hour half-life versus minutes for native IGF-1; systemic, not local.
- Reported community doses run 20–100 mcg daily; no human trials exist.
- Systemic IGF-1 signaling carries theoretical hypoglycemia and tumor-growth concerns.
Overview
What it is
IGF-1 LR3 (Long R3 IGF-1) is an engineered analog of insulin-like growth factor 1 with an arginine substitution at position 3 and a 13-amino-acid N-terminal extension. Those changes slash binding to IGF-binding proteins, leaving more free hormone to drive anabolic signaling at the IGF-1 receptor.
Pharmacokinetics
The modifications also extend circulation time: the estimated half-life is roughly 12 hours versus minutes for native IGF-1, with around 60% bioavailability. That makes LR3 systemic rather than local.
What the evidence says
Human PK and clinical data are essentially absent. What is known comes from in vitro potency work and animal infusion studies. IGF-1 LR3 is not an approved medication, and community dosing is anecdotal.
Reported dosing protocols
Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.
| Use case | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| Muscle growth (community) | 20–50 mcg (up to 100) | SubQ or IM | Once daily | 4–6 weeks |
Pharmacokinetic summary
- Model tier
- Simple (t½ + F, Tmax estimated)
- Half-life
- 12 hours
- Bioavailability
- 60%
- Typical dose
- 0.02–0.1 mg
Frequently asked questions
IGF-1 LR3 vs IGF-1 DES — which is which?
LR3 is the long-acting variant (~12-hour half-life), dosed once daily with systemic exposure. DES is the short-acting variant (~30 minutes), used for local site injection. Neither has human trial data.
Why is IGF-1 LR3 dosed only once a day?
The engineered resistance to IGF-binding proteins extends its half-life to roughly 12 hours, so a single daily injection maintains exposure. Shorter-acting IGF-1 variants need more frequent or site-specific dosing.
What are the main risks of IGF-1 LR3?
The acute risk is hypoglycemia, since IGF-1 cross-reacts with insulin signaling. The long-term concern is theoretical: systemic growth signaling could accelerate pre-existing tumors. No human safety data exists, so the real profile is unknown.
References
- Estimated — Arginine-substituted analog with reduced binding proteins and extended half-life.
- J Endocrinol 1995 — Long R3 IGF-I infusion (guinea pig) — Animal study: LR3 infusion drove organ growth while suppressing native IGF levels.
Related compounds
MGF (Mechano Growth Factor)
IGF-1 splice variant produced in response to mechanical load; involved in muscle repair signaling.
PEG-MGF (Pegylated MGF)
Pegylated mechano growth factor with extended half-life versus native MGF; used for recovery research.
IGF-1 DES
Truncated, highly potent IGF-1 variant with very short half-life; site-injection research compound.
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