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A specimen of the Hormonal drawer Drawer C · Hormonal

IGF-1 LR3

Research Only

A modified form of IGF-1 with an extended half-life due to reduced binding protein affinity. Used primarily in research for muscle growth and metabolic effects. Not approved for human use; significant safety concerns exist.

Long R3 IGF-1 · LR3-IGF-1 · Insulin-like Growth Factor 1 Long R3

Research evidence
Low

8 human studies

Preclinical
58%
Human research
17%

Based on 48 cited sources

Numeric assessment unreviewed

A historical numeric score is recorded but has not passed a current, compound-specific assessment review. No numeric score is displayed.

This is a limitation of the numeric assessment, not a measured absence of benefit. It does not re-review the separately recorded catalogue classification or establish efficacy or safety.

Scoring context and limitations
!
Evidence Level
low
Not FDA-approved.
Research Only
Identity
SCALE · 1:1 N-TERMINUS C-TERMINUS 83 AA · 9,116 Da
Also Known As
Long R3 IGF-1 • LR3-IGF-1 • Insulin-like Growth Factor 1 Long R3
Class
Modified growth factor analog
Length
83 amino acids
Mol. weight
9,116 Da
Sequence
MFPAMPLSSLFVNGPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA
Molecular Structure
M
F
P
A
M
P
L
S
S
L
F
V
N
G
P
R
T
L
C
G
A
E
L
V
D
A
L
Q
F
V
C
G
D
R
G
F
Y
F
N
K
P
T
G
Y
G
S
S
S
R
R
A
P
Q
T
G
I
V
D
E
C
C
F
R
S
C
D
L
R
R
L
E
M
Y
C
A
P
L
K
P
A
K
S
A
Hydrophobic
Polar
Positive
Negative

IGF-1 LR3 is a modified form of insulin-like growth factor 1, engineered to resist binding to IGF-binding proteins. This modification dramatically extends its biological half-life from minutes to hours while maintaining full receptor activity.

How It Works (Simplified)

IGF-1 LR3 drives muscle growth through four key mechanisms:

Protein Synthesis

Activates PI3K/Akt/mTORC1 pathway, directly stimulating ribosomal protein synthesis and muscle fiber hypertrophy.

Anti-Catabolic

Inhibits FOXO transcription factors, suppressing muscle breakdown genes MuRF1 and atrogin-1.

Satellite Cells

Promotes satellite cell proliferation and myoblast differentiation, supporting muscle fiber repair and regeneration.

Glucose Uptake

Stimulates GLUT4 translocation, enhancing glucose transport into muscle cells for energy and glycogen synthesis.

Key Research: Francis GL et al. (1992) first characterized Long [Arg3]-IGF-I (LR3-IGF-1) structure and demonstrated reduced IGF-binding-protein affinity with enhanced biological potency. PMID:1378742

Important Limitations

  • No randomized controlled trials in healthy adults for muscle building
  • Significant hypoglycemia risk due to insulin-like receptor activity
  • Cancer promotion concerns - IGF-1 signaling is mitogenic and anti-apoptotic
  • Long-term safety data is absent - most evidence is preclinical

Research Tools

i. PI3K/Akt/mTOR Pathway · Protein Synthesis
IGF-1 LR3IGF-1R bindingIRS-1 phosphorylationPI3KAktmTORC1 activation + FOXO inhibitionProtein synthesis + Reduced degradation
ii. Extended Half-Life Mechanism · Key Modification
Native IGF-1IGFBP binding (>99%)Sequestration12-15 min half-life IGF-1 LR3Arg3 + N-terminal extension<1% IGFBP binding20-30 hr half-life
Mechanism PI3K/Akt/mTORC1 pathway activation promoting protein synthesis
Established 12 direct studies
Benefit shown to enhance muscle protein synthesis and hypertrophy
Evidence Level
Moderate
2 Human
8 Animal
6 In Vitro
Mechanism FOXO transcription factor inhibition reducing protein degradation
Established 8 direct studies
Benefit shown to reduce muscle protein breakdown
Evidence Level
Moderate
1 Human
6 Animal
4 In Vitro
Mechanism Satellite cell proliferation and myoblast differentiation enhancement
Supported 6 direct studies
Benefit appears to support muscle regeneration and repair
Evidence Level
Low
5 Animal
4 In Vitro
Mechanism GLUT4 translocation increasing glucose uptake
Supported 5 direct studies
Benefit may improve glucose disposal in muscle tissue
Evidence Level
Low
1 Human
4 Animal
3 In Vitro
Mechanism Confidence
Established
Supported
Emerging
Evidence Level
High
Moderate
Low
Very Low

Reported positives

  • Localized muscle growth at injection sites reported
  • Enhanced recovery from intense training noted
  • Synergistic effects when combined with GH reported
  • Improved nutrient partitioning claimed

Reported negatives

  • Hypoglycemia risk is a significant safety concern
  • Potential to promote growth of existing tumors
  • Gut growth and organ enlargement concerns
  • Injection site pain and swelling common

“Used primarily in advanced bodybuilding circles. Significant safety concerns limit broader adoption.”

Self-reported, unverified accounts — not clinical evidence and no substitute for the cited research. Anecdotes are prone to selection bias and placebo effects.

Phase 01 1
Acute

IGF-1 LR3's extended half-life (20-30 hours vs 12-15 minutes for native IGF-1) means effects persist longer per dose. Hypoglycemia risk exists within hours of administration.

PMID:1378742
Phase 02 2
Week 1-4

Animal studies typically used treatment periods of weeks. Muscle protein synthesis increases may be detectable early. Most users in performance contexts report cycles of 4-8 weeks.

PMID:7683875
Phase 03 3
Long-term

Long-term human safety data for IGF-1 LR3 does not exist. Native IGF-1 (mecasermin) long-term use has been associated with various adverse effects including tonsillar hypertrophy and potential cancer risk concerns.

Research-based observations

This timeline reflects observations from published clinical and preclinical studies. Individual responses may vary significantly. This is not a guarantee of effects or a dosing schedule. Consult qualified healthcare providers for personalized guidance.

Synergistic
Compatible
Caution
Avoid

Hgh

Synergistic
Synergistic

HGH stimulates endogenous IGF-1 production. Adding exogenous IGF-1 LR3 may amplify anabolic effects but also compounds risks including hypoglycemia and potential cancer promotion.

Mgf

Compatible
Compatible

MGF (Mechano Growth Factor) is an IGF-1 splice variant. Different kinetics and localization may provide complementary effects, but combined safety is not established.

BPC-157

Compatible
Compatible

Different regenerative mechanisms - BPC-157 for tissue healing, IGF-1 LR3 for muscle growth. Theoretical complementary use.

TB-500

Compatible
Compatible

TB-500 promotes tissue repair via actin regulation while IGF-1 LR3 drives muscle hypertrophy. Different mechanisms may be complementary.

Insulin

Caution
Caution

Both cause hypoglycemia through different mechanisms. Combined use dramatically increases risk of severe hypoglycemia.

Igf-1

Avoid
Avoid

Both act on the same receptor. Combining provides no additional benefit and increases risk of hypoglycemia and other adverse effects.

Research Note: Interaction data is based on published literature, mechanistic understanding, and theoretical considerations. Most peptide combinations lack direct clinical study. This information is for educational purposes only and does not constitute medical advice. Always consult qualified healthcare providers.

48 Sources 8 Human 28 Preclinical

Key Studies Cited

In Vitro Rommel C et al. 2001
PMID:11715022
Animal Tomas FM et al. 1993
PMID:7683875
In Vitro Sandri M et al. 2004
PMID:15109499
In Vitro Stitt TN et al. 2004
PMID:15125842
In Vitro Florini JR et al. 1996
PMID:8897022
Animal Gehrig SM et al. 2008
PMID:18567600
In Vitro Bilan PJ et al. 1992
PMID:1312027
Animal Moxley RT et al. 1990
PMID:2221058

Use the source links in the research discussion above to inspect the referenced records.

This dossier synthesizes available evidence from peer-reviewed literature, regulatory documents, and clinical trial registries. Evidence strength labels summarize the cited material for this entry and should be read alongside its population, model, and study limitations.

For complete methodology details, see our Methodology page.

Important Disclaimer

This dossier is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before making health decisions.

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1 comparison

Conditions Studied

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