RESEARCH MONOGRAPH · KDC-MN-200

Cycloprolylglycine (CPG)

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

51/100

Endogenous Russian dipeptide. Almost certainly the active metabolite of noopept. Almost no Western literature

Cycloprolylglycine is one of those compounds that exists in a strange transcontinental literature gap. It's been identified as both an endogenous neuropeptide (Gudasheva group, Russian Academy of Medical Sciences, 1990s) and as the in vivo metabolite of noopept (N-phenylacetyl-L-prolylglycine ethyl ester), which means most of what we functionally know about noopept's pharmacology probably runs through CPG.

The mechanism story, as the Russian literature presents it, involves AMPA receptor potentiation and possibly BDNF / NGF upregulation in hippocampal neurons. CPG appears to potentiate kainate and AMPA currents at low concentrations in patch-clamp experiments, and the parent compound noopept has demonstrated some pro-cognitive effects in rodent models of stress-induced learning impairment. The translation to humans is where it gets thin, because almost all of the clinical data comes from Eastern European medical literature that hasn't been independently replicated by Western groups.

What we like, honestly, is the intellectual honesty of the Russian noopept program. They identified the metabolite, characterized its endogenous role, and built a coherent pro-drug strategy around it (noopept being far more orally bioavailable and crossing the BBB efficiently to deliver CPG-equivalent activity). That's reasonable pharmacology, not just folk-supplement vibes.

What we dont know: how meaningful any of this is at the doses humans typically use. Noopept's 10-20 mg sublingual dose generates CPG plasma levels that may or may not reach effective brain concentrations. Direct CPG administration is rarely studied because oral bioavailability of the dipeptide itself is presumably worse than the noopept pro-drug. There's basically no Western RCT data, and the Russian literature has well-documented quality issues that make it hard to evaluate without the original protocols.

Sourcing is the harder problem. CPG is a simple cyclic dipeptide that's not difficult to synthesize, but legitimate research-grade reference material is harder to find than for most short peptides because demand is essentially limited to a small academic and gray-market niche. HPLC verification matters more than for commodity peptides.

Worth keeping in rotation as a research tool? for hippocampal AMPA pharmacology, maybe. The literature is too thin to have a strong opinion. This is one where we'd genuinely defer to the next decade of work rather than overstate the current evidence base.

Evidence: 30
Mechanism: 55
Reliability: 45
Safety: 65
Sourcing: 55
Value: 60
Signal: 45
Staying power: 50

Plain-language summary Intrigue 60 / 100

Cycloprolylglycine (CPG) is a cyclic dipeptide your body produces naturally and stores in spinal fluid. It is the active metabolite of noopept; when you take noopept your body converts it to CPG, which does most of the work. Researchers study it on its own to understand brain mechanisms. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Endogenous dipeptide / noopept metabolite

An endogenous dipeptide present in mammalian CSF; the principal active metabolite of noopept and a research probe for endogenous nootropic mechanisms.

Abstract

Cycloprolylglycine (CPG; cyclic Pro-Gly dipeptide) is an endogenous cyclic dipeptide identified in human cerebrospinal fluid and brain tissue. The compound is the principal active metabolite of noopept (formed by enzymatic cyclization after the parent compound's hydrolysis) and has been investigated as an independent research probe. Pharmacology overlaps with noopept: BDNF and NGF upregulation, antioxidant effects, modulation of NMDA and AMPA receptor expression, modest cholinergic facilitation. CPG itself is sold as a research peptide for investigators studying the noopept mechanism without the parent compound's prodrug pharmacology. Pharmacokinetics: plasma half-life ~2 hours; oral bioavailability presumed adequate. Doses are not formally established; rodent doses scale to micrograms per kilogram.

Mechanism of action

Endogenous cyclic dipeptide; BDNF/NGF upregulation, NMDA/AMPA modulation. Active metabolite of noopept.

Reported research dose ranges

Not formally established; sub-milligram research-grade doses.

References

Gudasheva TA, et al. Identification of cycloprolylglycine in mammalian brain and its activity. Bull Exp Biol Med 1996.

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KDC-MN-200

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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Cycloprolylglycine (CPG)

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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