Cyclic Glycine-Proline
cGP | IGF-1 Bioavailability Regulator & Neuroprotective Peptide
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What is Cyclic Glycine-Proline?
Cyclic glycine-proline (cGP) is a very small, ring-shaped peptide that the body makes naturally in blood, breast milk, and spinal fluid. Researchers study how it helps balance the availability of a growth-related hormone called IGF-1, and how it may support brain-cell protection and cognitive research. It's sold here strictly as a research chemical for laboratory study, not for human or animal use.
Key terms:
Cyclic Glycine-Proline is a cyclic dipeptide (2,5-diketopiperazine).
Cyclic glycine-proline (cGP) is a tiny natural peptide of two amino acids joined in a ring. Chemists group it with the 2,5-diketopiperazines. The human body makes it on its own, and it is found in blood plasma, breast milk, and the fluid around the brain and spinal cord. It forms when the body breaks down insulin-like growth factor-1 (IGF-1). It then helps set how much IGF-1 is free to act, by competing with IGF-1 to bind a carrier protein called IGFBP-3. Research describes protective effects on nerves and the heart, plus nootropic (thinking and memory) effects. Clinical trials have reported benefits for cognitive function, stroke recovery, and metabolic health.
Key research areas
- Neuroprotection and cognitive enhancement
- IGF-1 optimization through IGFBP-3 competition
- Cardiovascular support
- Metabolic health benefits
- Convenient oral administration
- Crosses blood-brain barrier
Researched dosing
This table shows how researchers structure study designs with cGP — the oral dose ranges used in published research and blackcurrant-extract studies, presented as methodology reference, not usage instructions.
| Phase | Dose | Frequency | Route |
|---|---|---|---|
| General cognitive studies | 20-40 μg | 1x daily | Oral (capsule) |
| Neuroprotection and longevity models | 40-50 μg | 1x daily | Oral (capsule) |
| Metabolic and cardiovascular studies | 40-100 μg | 1x daily | Oral (capsule) |
| Blackcurrant-extract studies | 300 mg BCA | 2x daily | Oral (capsule) |
Commonly cycled 12 weeks on, 0+ weeks off.
How it works
At the cell level, cGP research looks at how the peptide competes for binding sites that control IGF-1 availability, and how it may adjust activity at certain brain-signaling receptors — the terms below just name those pathways.
cGP competes with IGF-1 for binding to IGFBP-3, thereby regulating the amount of bioavailable IGF-1 in circulation. It normalizes IGF-1 function - promoting activity when insufficient and inhibiting when excessive. Also acts as positive allosteric modulator of AMPA and GABA-A receptors and increases BDNF levels.
Molecular data
These figures — molecular weight, structure, chain length — are the chemistry fingerprint researchers use to confirm a cGP sample's identity; at just two amino acids joined in a ring, it's one of the smallest peptides in this encyclopedia.
- Weight
- 154.17 Da
- Length
- 2 amino acids
- Type
- Cyclic dipeptide (2,5-diketopiperazine)
cyclo(Gly-Pro)
Research applications
This section lists the body systems and research areas scientists have studied for cGP — mostly cognitive and metabolic research — summarizing what's been studied in the literature, not medical claims about people.
Neurological
Research shows higher cGP levels correlate with better memory retention in elderly. cGP increases BDNF and acts on AMPA receptors for pro-cognitive effects. Protects neural stem cells from oxidative stress via Akt/MDM2-p53 pathway; demonstrated efficacy in stroke and hypoxic-ischemic brain injury models. Mouse studies show significant reduction in amyloid plaque load and improved spatial memory. Clinical study showed increased CSF cGP levels and reduced anxiety/depression scores in PD patients following supplementation.
Metabolic
Supports metabolic health through IGF-1 bioavailability regulation and cardioprotective properties.
Recovery
Supports recovery processes through neuroprotective mechanisms and IGF-1 normalization.
Dosage reference
- Doses used in research
- 20–50 μg cGP, or 300–600 mg blackcurrant extract
- Frequency in studies
- 1-2x daily
- Handling
- Reconstituted solution — research use only; not for administration
- Timeline reported in studies
- Cognitive effects 2-4 weeks, full benefits 4-12 weeks
- Storage
- Room temperature, cool dry place
- Cycle length
- 4-12 weeks or continuous
- Break between cycles
- Optional - can be used continuously
Interactions
This list shows which other cognitive-research peptides and compounds are studied alongside cGP, and why.
Reconstitution & storage
cGP is typically studied as a pre-made capsule or natural extract rather than an injectable, so this section covers handling notes for oral research use.
- cGP is typically available as pre-made capsules or in blackcurrant-derived supplements.
- If using raw powder, measure precise dose with accurate milligram scale.
- Maintain consistent daily timing for best results.
- Store the reconstituted solution refrigerated (2–8°C), labeled with the date and concentration, for laboratory research use only.
Lyophilized: Room temperature, cool dry place, use within As per manufacturer specification
Reconstituted: 2-6°C, use within Store per formulation guidance; no refrigeration typically required for oral formulations
Quality indicators
These are the documentation and sourcing checks researchers use to confirm a cGP sample or extract is properly manufactured and tested before it goes into a study.
Third-party tested - Quality cGP supplements should have independent purity and potency testing from reputable labs
Clear concentration labeling - Product should clearly state cGP content per serving (typically in micrograms)
Natural source (blackcurrant-derived) - New Zealand blackcurrant extracts are a well-researched natural source of cGP
Proper packaging - Sealed containers protected from moisture and light to maintain stability
No concentration specified - Avoid products that don't clearly state cGP content or use only vague descriptions
Excessive claims - Be wary of products making extreme therapeutic claims not supported by research
What to expect
This timeline summarizes what the available research literature reports at each stage of a study — research context for comparing studies, not a personal-results promise.
Possible subtle improvements in mental clarity.
Enhanced cognitive function and focus may become noticeable.
Neuroprotective and metabolic benefits accumulating.
Optimal IGF-1 regulation and sustained cognitive support.
Safety notes
This section covers handling and regulatory notes for cGP — research-use-only scope, since long-term human data remains limited.
- Consult healthcare provider if taking medications affecting IGF-1 or growth hormone
- Limited long-term human data - most studies are short to medium term
Regulatory status
- Not approved by the FDA for any indication.
- Supplied and described for laboratory research use only — not for human or veterinary use.
Community data
Community Insights
Based on data the community reported. Not clinical proof.
References
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.
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.
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.