Cyclic Glycine-Proline
cGP | IGF-1 Bioavailability Regulator & Neuroprotective Peptide
Cyclic glycine-proline (cGP) is a naturally occurring small cyclic dipeptide belonging to the 2,5-diketopiperazine family. It is endogenous to the human body, found in plasma, breast milk, and cerebrospinal fluid. cGP is a metabolite of insulin-like growth factor-1 (IGF-1) and plays a key role in regulating IGF-1 bioavailability by competing with IGF-1 for binding to IGFBP-3. Research suggests cGP has neuroprotective, nootropic, and cardioprotective properties, with clinical trials showing benefits for cognitive function, stroke recovery, and metabolic health.
Daily dose
20-100 μg
Frequency
1-2x daily
Cycle length
4-12 weeks
Storage
Room temp
Key benefits
Neuroprotection, cognitive enhancement, IGF-1 optimization, cardiovascular support, metabolic health, oral bioavailability, crosses blood-brain barrier
How it works
Competes with IGF-1 for IGFBP-3 binding to regulate bioavailable IGF-1. Acts as positive allosteric modulator of AMPA and GABA-A receptors. Increases BDNF levels for neuroprotective effects.
Dosage protocols
Goal
General cognitive support
Dose
20-40 μg · 1x daily
Route
Oral
Goal
Neuroprotection
Dose
40-50 μg · 1x daily
Route
Oral
Goal
Via blackcurrant extract
Dose
300-600 mg · 1-2x daily
Route
Oral
Research indications
neurological
metabolic
recovery
Administration
Interactions
Safety notes
Endogenous compound naturally found in human body
Generally well-tolerated in clinical studies
No significant adverse events reported
Start with lower dose to assess response
Consult healthcare provider if on medications affecting IGF-1
Research studies
Alzheimer's Mouse Model Study (2023)
APP/PS1 mice | 20 mg/kg intranasal | 28 days
cGP treatment significantly improved spatial memory and reduced amyloid plaque density in hippocampus (42.3 to 14.5 plaques/mm²) and cortex (42.7 to 15.4 plaques/mm²) in Alzheimer's disease mouse model.
View study →Stroke Recovery & Cognitive Function Review (2023)
Review | Multiple clinical observations | cGP/IGF-1 ratio analysis
Comprehensive review showing stroke patients with higher cGP/IGF-1 ratios have more favorable outcomes. Elderly with higher cGP levels show better memory retention. Decrease in cGP/IGF-1 ratio with age associated with dementia.
View study →Parkinson's Disease Clinical Study (2018)
Human subjects | 11 PD patients | 28 days blackcurrant supplementation
Blackcurrant anthocyanin supplementation (containing cGP) increased cerebrospinal fluid cGP by 74% and reduced anxiety/depression scores in Parkinson's patients. Demonstrated oral bioavailability and brain penetration.
View study →IGF-1 Homeostasis Regulation Study (2014)
Cell culture & animal models | Various concentrations | IGFBP-3 binding analysis
Demonstrated that cGP regulates IGF-1 bioavailability through competitive binding to IGFBP-3. Higher cGP/IGF-1 ratios increased unbound IGF-1, while lower ratios decreased it. Shows cGP can normalize IGF-1 function.
View study →