Side-by-side · Research reference

IGF-1 LR3vsPT-141

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

BFDA-ApprovedHUMAN-REVIEWED13/41 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

PT-141

MC4R Agonist · FDA-Approved (HSDD)

1.75 mgPer doseVYLEESI (bremelanotide injecti 2019

Pre-sexTimingVYLEESI (bremelanotide injecti 2019

~2.7 hrHalf-lifeVYLEESI (bremelanotide injecti 2019

SQ · Abdomen / thigh · ≥45 min before sex

01Mechanism of Action

Parameter

IGF-1 LR3

PT-141

Primary target

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

Melanocortin-4 receptor (MC4R) in hypothalamusSimerly 2023 VYLEESI (bremelanotide injecti 2019

Pathway

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

MC4R agonism in paraventricular nucleus → autonomic + neuroendocrine sexual arousal pathwaysSimerly 2023

Downstream effect

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

Increased sexual desire and arousal; central rather than peripheral mechanismClayton 2015

Feedback intact?

No — exogenous IGF analogue bypasses GH-mediated regulation

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Origin

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

Cyclic 7-AA peptide derived from α-MSH (agonist Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-OH cyclic)VYLEESI (bremelanotide injecti 2019

Antibody development

—

02Dosage Protocols

Parameter

IGF-1 LR3

PT-141

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.

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Evidence basis

Animal / in vitro only

FDA-approved (HSDD pre-menopausal women)VYLEESI (bremelanotide injecti 2019 Clayton 2015

Human use

Not FDA-approved; no published human trials

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Standard dose

—

1.75 mg SQVYLEESI (bremelanotide injecti 2019

Single dose ≥45 min before anticipated sexual activity. Max 1 dose / 24 hr.

Frequency

—

PRN, max 8 doses / month

Lower / starter dose

—

1 mg (off-label)

Duration

—

PRN; reassess if no benefit after 8 doses

Reconstitution

—

Pre-filled commercial pen (Vyleesi). Research vial: bacteriostatic water.

Timing

—

≥45 min before sexual activity

Half-life

—

~2.7 hrVYLEESI (bremelanotide injecti 2019

03Metabolic / Fat Loss Evidence

Parameter

IGF-1 LR3

PT-141

Mechanism

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

—

Direct lipolytic evidence

Minimal — primarily anabolic/anti-apoptotic in literature

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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

PT-141

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.

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Oocyte degeneration

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

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Unregulated anabolism

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

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Unknown human safety profile

No published human trials; safety data absent

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Nausea

—

Common (~40%); often transientVYLEESI (bremelanotide injecti 2019

Flushing

—

Common, transient

Injection site reaction

—

Erythema, mild pain

Headache

—

Common

Hyperpigmentation (focal)

—

Rare focal skin darkening; reversible after discontinuationVYLEESI (bremelanotide injecti 2019

Hypertension (transient)

—

Mean ↑6 mmHg systolic peaking ~4 h post-dose; resolves within 12 hVYLEESI (bremelanotide injecti 2019

Pregnancy / OB

—

Contraindicated

Cardiovascular disease

—

Use caution; transient BP rise

Absolute Contraindications

IGF-1 LR3

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

PT-141

·Uncontrolled hypertension
·Known cardiovascular disease (caution)
·Pregnancy

Relative Contraindications

IGF-1 LR3

·Diabetes or glucose intolerance
·Family history of cancer

PT-141

·Pre-existing hyperpigmentation disorders
·MC4R-pathway-dependent psychiatric conditions

05Administration Protocol

Parameter

IGF-1 LR3

PT-141

1. Research use only

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

Vyleesi: pre-filled auto-injector. Research vial: 2 mL bacteriostatic water per 10 mg → 5 mg/mL.

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 or thigh.

3. Reconstitution (research)

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

≥45 min before sexual activity for peak effect. Effect persists ~6–8 h.

4. Stability

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

Vyleesi: room temp ≤30 °C. Research vial: refrigerate after reconstitution.

5. Needle

—

Auto-injector (Vyleesi) or 29–31G, 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)

PT-141

— no documented stacks