Side-by-side · Research reference

IGF-1 LR3vsRetatrutide

Side-by-side comparison across mechanism, dosage, evidence, side effects, administration, and stack synergies. Citations on every claim where available.

AAnimal-StrongHUMAN-REVIEWED10/58 cited

BPhase 2HUMAN-REVIEWED10/41 cited

IGF-1 LR3

IGF-1 Analogue · Research

3–10×Potency vs IGF-I

Low IGFBPBinding affinity

ResearchStatus

Research only · SQ typical in animal models

Retatrutide

Triple-receptor agonist · Phase 3

1–12 mgWeekly doseJastreboff 2023

24.2%Body-weight ↓Jastreboff 2023

~6 daysHalf-life (est)

SQ · Abdomen · Once weekly

01Mechanism of Action

Parameter

IGF-1 LR3

Retatrutide

Primary target

IGF-1 receptor (IGF-1R)McTavish 2009

GLP-1R + GIPR + Glucagon receptor (triple agonism)Jastreboff 2023

Pathway

IGF-1R → IRS-1 → PI3K/Akt → Cell proliferation, protein synthesis, anti-apoptosisMuhlbradt 2009

Triple-receptor activation → ↑insulin (GLP-1+GIP), ↓gastric emptying, ↑lipid handling, ↑energy expenditure (glucagon component)Jastreboff 2023

Downstream effect

Enhanced cell proliferation, muscle anabolism, inhibition of apoptosis, increased telomerase activity

Maximal weight loss across class. Glucagon component drives lipolysis and energy expenditure beyond GLP-1+GIP aloneJastreboff 2023

Feedback intact?

No — exogenous IGF analogue bypasses GH-mediated regulation

—

Origin

Synthetic 83-AA analogue: 13-AA N-terminal extension + Arg substitution at position 3

Synthetic peptide engineered for balanced affinity at three incretin / glucagon receptorsJastreboff 2023

Antibody development

—

02Dosage Protocols

Parameter

IGF-1 LR3

Retatrutide

Research dose (animal models)

Variable by protocol and species

In vivo murine atherosclerosis studies used sustained delivery.

—

In vitro typical concentration

10–1000 ng/mLThomas 2007

Dose-dependent effects on follicle growth and estradiol production.

—

Half-maximal stimulation

0.6 nM LR3 vs 1.5 nM native IGF-1Price 2004

2.5-fold greater potency in lung fibroblast proliferation.

—

Evidence basis

Animal / in vitro only

Phase 2 trial; Phase 3 ongoingJastreboff 2023

Human use

Not FDA-approved; no published human trials

—

Standard dose

—

12 mg / week (max efficacy)Jastreboff 2023

Phase 2 trial dose. Phase 3 dosing TBD.

Frequency

—

Once weekly

Titration schedule

—

2 mg → 4 mg → 8 mg → 12 mg over 16 weeks

Duration

—

Indefinite for chronic indication (presumed)

Reconstitution

—

Investigational; not commercially available

Timing

—

Any time of day

Half-life

—

~6 days (estimated from class)

03Metabolic / Fat Loss Evidence

Parameter

IGF-1 LR3

Retatrutide

Mechanism

IGF-1R activation → lipolytic signaling; secondary to anabolic effects

—

Direct lipolytic evidence

Minimal — primarily anabolic/anti-apoptotic in literature

—

Atherosclerotic plaque effects

Reduced stenosis and core size in ApoE-KO micevon 2011

Plaque stabilization via vSMC phenotype modulation, not direct fat loss.

—

Human data

None published

—

04Side Effects & Safety

Parameter

IGF-1 LR3

Retatrutide

Hypoglycemia risk

Theoretical — IGF-1 analogues can lower blood glucose

—

Excessive cell proliferation

Mitogenic signaling; theoretical tumor promotion risk

—

Telomerase activation

2–10-fold increase in prostate cancer cells (PC-3, DU-145, LAPC-4)Wetterau 2003

Critically involved in cancer cell immortalization.

—

Oocyte degeneration

Increased oocyte degeneration at high doses (≥1000 ng/mL) in bovine folliclesThomas 2007

—

Unregulated anabolism

Bypasses physiological GH/IGF-1 feedback; no pulsatility control

—

Unknown human safety profile

No published human trials; safety data absent

—

GI symptoms

—

Nausea, vomiting, diarrhea (very common, dose-dependent)Jastreboff 2023

Heart rate

—

↑ resting HR (3–7 bpm at 12 mg)Jastreboff 2023

Glucose handling

—

Glycemic improvement; rare hyperglycemia from glucagon component

Pancreatitis risk

—

Class warning

Thyroid C-cell tumours

—

Class warning (presumed)

Pregnancy / OB

—

Avoid (insufficient data)

Absolute Contraindications

IGF-1 LR3

·Active malignancy or history of cancer
·Not approved for human use

Retatrutide

·MTC personal or family history (presumed class effect)
·Pregnancy / breastfeeding

Relative Contraindications

IGF-1 LR3

·Diabetes or glucose intolerance
·Family history of cancer

Retatrutide

·Severe gastroparesis
·History of pancreatitis
·Severe cardiovascular disease (HR signal)

05Administration Protocol

Parameter

IGF-1 LR3

Retatrutide

1. Research use only

IGF-1 LR3 is not FDA-approved for human use. All administration data derives from animal or in vitro studies.

Investigational peptide. Research vials reconstituted with bacteriostatic water per label.

2. Typical research route

Subcutaneous or intraperitoneal injection in animal models. In vitro: added directly to culture medium at concentrations of 10–1000 ng/mL.Thomas 2007

SQ — abdomen, thigh, or upper arm. Rotate weekly.

3. Reconstitution (research)

Lyophilised powder reconstituted in sterile water or buffered saline per manufacturer protocol. Store at 2–8 °C after reconstitution.

Once weekly, same day.

4. Stability

Enhanced stability vs native IGF-1 due to reduced IGFBP binding; exact half-life in vivo not fully characterized in humans.

Refrigerate 2–8 °C. Light-protected.

5. Needle

—

27–31G, 4–8 mm insulin syringe.

06Stack Synergy

IGF-1 LR3

+ GHRP-6

Multi-pathway

View GHRP-6 →

GHRP-6 stimulates endogenous GH release, which drives hepatic IGF-1 synthesis. IGF-1 LR3 provides exogenous, IGFBP-resistant IGF signaling. Combining upstream GH stimulation with downstream IGF receptor activation creates a dual-pathway anabolic effect. However, this bypasses natural feedback and carries compounded mitogenic risk.

GHRP-6: 100–200 mcg SQ · 2–3× daily
IGF-1 LR3: Research doses variable · post-workout typical in animal models
Note: Research context only — no human protocols exist
Primary benefit: Theoretical maximal anabolic signaling (GH + IGF axes)

+ Ipamorelin

Multi-pathway

View Ipamorelin →

Ipamorelin (selective GHRP) stimulates pulsatile GH release without cortisol/prolactin elevation. IGF-1 LR3 directly activates IGF-1R independent of GH. This stack targets both upstream (GH secretion) and downstream (IGF receptor) nodes but eliminates physiological feedback, raising safety concerns around unchecked proliferation.

Ipamorelin: 200–300 mcg SQ · evening
IGF-1 LR3: Research doses only · timing variable
Caution: No human data; animal/in vitro only
Primary benefit: Dual-axis anabolic signaling (theoretical)

Retatrutide

— no documented stacks