Cyclic Glycine-Proline (cGP) Dosage Guide, Benefits & Side Effects

There is no established, universally agreed-upon human dosage for cGP. Animal studies use milligram-per-kilogram doses that vary by study design and cannot be reliably converted into a human dose. Commercial supplement products (marketed as ingredients like 'cGP-PRo') advertise a 'standardized' dose derived from blackcurrant extract, but these are proprietary formulations, not peer-reviewed clinical dosing protocols. Anyone considering a cGP-containing product should treat dosing claims from vendors with caution and recognize that formal, peer-reviewed human dosing studies are lacking.

Because cGP is an endogenous compound the body already produces and encounters through diet, several review papers describe it as having a favorable, 'drug-like' safety profile in preclinical work, with no major adverse effects reported in the studies conducted so far. However, formal human safety/toxicology data, drug-interaction studies, and long-term safety trials for supplemental or research-grade cGP are limited. As with any research compound, potential buyers should not assume an absence of documented side effects means the compound is proven safe for general human supplementation, especially at doses above what the body normally produces.

cGP itself is a naturally occurring dipeptide sold in some jurisdictions as a dietary supplement ingredient (e.g., derived from blackcurrant extract) and is also available from research chemical suppliers labeled 'not for human consumption.' It is distinct from NNZ-2591, a synthetic, chemically modified analog of cGP being developed by a pharmaceutical company as a prescription drug candidate; NNZ-2591 is investigational and not commercially available outside of clinical trials. Regulatory status for cGP supplements varies by country, and research-labeled peptide products are not approved by regulators (e.g., the FDA) for human use — they are sold for laboratory/research purposes only.

cGP is often discussed alongside GPE (glycine-proline-glutamate) and IGF-1 itself, since cGP is a downstream metabolite in that same pathway. Compared with full-length IGF-1 or growth-hormone-releasing peptides, cGP does not directly stimulate growth hormone or IGF-1 production; instead it modulates how much of the body's existing IGF-1 is 'free' and biologically active by competing with IGFBP-3 binding. This is why researchers position it as a regulator of IGF-1 function/bioavailability rather than a growth-promoting hormone secretagogue in its own right.