IGF-1 LR3

Other Research compound (not approved for human use)

Insulin-like growth factor 1 analog · also known as Long R3 IGF-1, LR3-IGF-I, Long-R3 insulin-like growth factor 1

For reference only — not medical advice. Figures are commonly reported values compiled from published sources and may be wrong or out of date. Many compounds listed are not approved for human use. Talk to a licensed clinician before using any compound.

IGF-1 LR3 (Long R3) is an 83-amino-acid IGF-1 analog with an arginine substitution at position 3 and a 13-residue N-terminal extension. These changes sharply lower its affinity for IGF-binding proteins, so more of the peptide is free to act on the IGF-1 receptor. It is widely used as a cell-culture supplement and has been studied in animals; it is not a drug approved for people. It is different from mecasermin, the approved recombinant IGF-1.

Commonly reported dosing (1 mg vial)

Reconstituted with 3 mL → 0.333 mg/mL.

Phase	Dose	Volume	U-100 units
Starting	20 mcg	0.06 mL	6
Standard	40 mcg	0.12 mL	12
Higher	50 mcg	0.15 mL	15

Frequency: Once daily · Half-life: Not well characterized in humans

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Commonly reported dose escalation

Weeks	Dose	Volume	U-100 units
Weeks 1-2	20 mcg	0.06 mL	6
Weeks 3-4	40 mcg	0.12 mL	12
Week 5+	50 mcg	0.15 mL	15

Higher steps may need a larger vial or more than one draw. Escalation schedules vary; dosing decisions belong to a licensed clinician.

Commonly reported reconstitution steps

Vials are usually brought to room temperature (about 15-20 minutes) first.
3 mL of bacteriostatic water is added slowly down the inside wall of the 1 mg vial.
The vial is swirled gently until clear, not shaken.
This gives 0.33 mg/mL. Mixed vials are typically labeled with the date and refrigerated.

Storage

Before mixing: Sealed vials are commonly stored refrigerated (2-8 °C) and protected from light, or frozen for long-term storage.

After mixing: Reconstituted solution is commonly kept refrigerated (2-8 °C), protected from light, and not frozen.

Commonly used within 28 days of mixing.

How it works

It activates the IGF-1 receptor like native IGF-1, driving PI3K/Akt and MAPK signaling that supports cell proliferation and protein synthesis. Weak IGFBP binding means it avoids the normal buffering by carrier proteins.

Researched for

In rats, LR3 IGF-I was about 1.5- to 2-fold more potent than IGF-I for weight gain and organ growth when infused, and stayed more potent when given by once-daily injection.
Studied in animal models of muscle loss and catabolism.
Used extensively as a growth supplement in cell culture and biotechnology.

Notes

IGF-1 has insulin-like effects; hypoglycemia is a recognized concern for IGF-1 products, and reference charts discuss pairing doses with food.
No controlled human trials of the LR3 analog were found; evidence is animal and in vitro.
IGF-1 signaling is also implicated in tumor growth, a concern for long-term exposure.
Detected in anti-doping testing; prohibited in competitive sport.