Muscle & Growth Hormone
IGF-1 LR3
Long-Arg3 IGF-1 · long-acting analog
What it is
IGF-1 LR3 is a modified version of natural insulin-like growth factor 1 (the main downstream effector of growth hormone). Two changes: (1) Arg substituted at position 3 to reduce binding to IGF-binding proteins; (2) a 13-amino-acid extension at the N-terminus that further extends half-life. Result: ~30 hours of action vs. ~10 minutes for native IGF-1.
How it works
IGF-1 is the actual signal that drives muscle hypertrophy and tissue growth downstream of GH. LR3 produces direct anabolic effects without needing the pituitary in the loop. Activates muscle satellite cells, increases protein synthesis, and triggers cell proliferation.
Benefits
- Strongest muscle-building peptide available
- Direct hyperplasia (new muscle cell creation, not just growth of existing cells)
- Improved nutrient partitioning
- Enhanced recovery
- Some neuroprotective effects
Timeline
- Week 1–2
- Stronger pumps; increased appetite; faster recovery.
- Week 4–6
- Visible mass gains; improved skin/recovery.
- Week 6–8
- Peak gains; cycle off mandatory.
Dosing & titration
Standard dose20–80 mcg subQ daily
Cycle length4–6 weeks ON, then 4–6 weeks OFF (mandatory due to receptor desensitization)
TimingPost-workout or pre-bed
When to titrate upStart at 20–30 mcg for 1–2 weeks. Don't exceed 80 mcg/day — risks rise dramatically without proportional muscle gain.
Side effects & risks
- Hypoglycemia (lower blood sugar) — carry sugar/snacks
- Increased risk of carpal tunnel symptoms
- Joint pain
- Organ enlargement at chronic high doses (heart, liver, intestines)
- Acromegaly-like features at extreme doses
Cancer-risk discussion is real. IGF-1 is implicated in cancer cell proliferation. Contraindicated for anyone with current or recent cancer history. Get baseline IGF-1 and recheck regularly. Eat carbs around dosing to prevent hypoglycemia. Advanced users only.
Typical price
$200–$400/mo1 mg vial from a 503A compounding pharmacy. One of the more expensive peptides.
Studies
- Search PubMed for IGF-1 LR3 — PubMed searchLive PubMed search
- Tomas FM et al. The effect of IGF-I and Long-Arg3-IGF-I on protein synthesis and degradation — Mechanism in muscle. PubMedBiochemical Journal, 1992
Educational reference only. Not medical advice. Not FDA-approved. Use only under medical supervision.