P-21
Nootropic PeptidePreclinicalAlso known as: P21, Cyclo(L-prolyl-glycine), Cyclo-Pro-Gly, Russian P-21, Selank Fragment
P-21 is a synthetic cyclic dipeptide — Cyclo(L-prolyl-glycine) — derived from the Selank/Semax C-terminal Pro-Gly-Pro motif. It was isolated and characterized by the Institute of Molecular Genetics at the Russian Academy of Sciences as a metabolic fragment of Selank, and shown in animal studies to recapitulate much of Selank's anxiolytic and nootropic profile in a smaller, more BBB-penetrant molecule. Unlike linear peptides that require intranasal administration to bypass enzymatic degradation, P-21's cyclic structure confers oral bioavailability — a significant practical advantage.
Overview
At A Glance
Mechanism (per published Russian-language research):…
Mechanism of Action
Mechanism (per published Russian-language research):
- GABAergic modulation — increases GABA-A receptor expression in hippocampus and amygdala without direct binding (similar to Selank's anxiolytic mechanism without benzodiazepine-style sedation)
- BDNF and NGF upregulation — increases neurotrophic factor expression after acute and chronic dosing
- Anti-inflammatory — reduces TNF-α and IL-1β in models of LPS-induced neuroinflammation
- Cyclic structure — confers oral bioavailability and improved BBB penetration vs. linear peptide parents
Overview
P-21 is a synthetic cyclic dipeptide — Cyclo(L-prolyl-glycine) — derived from the Selank/Semax C-terminal Pro-Gly-Pro motif. It was isolated and characterized by the Institute of Molecular Genetics at the Russian Academy of Sciences as a metabolic fragment of Selank, and shown in animal studies to recapitulate much of Selank's anxiolytic and nootropic profile in a smaller, more BBB-penetrant molecule.
Unlike linear peptides that require intranasal administration to bypass enzymatic degradation, P-21's cyclic structure confers oral bioavailability — a significant practical advantage. Reported research applications include stress-induced cognitive deficit reversal, anxiolytic effects without sedation, and acute neuroprotection in MCAO (middle cerebral artery occlusion) stroke models.
As of 2026, P-21 is not FDA-approved. The published literature is concentrated in Russian-language journals from the 2010s; English-language peer-reviewed studies are sparse.
Chemical Information
IUPAC Name
Not yet available
CAS Number
Not yet available
Molecular Formula
C7H10N2O2
Molecular Mass
154.17 g/mol
Dosing & Protocols
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Research
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Interactions
Interaction and contraindication data is being compiled for P-21. Check back soon.
General Safety Note
Always consult a qualified healthcare professional before combining research compounds. Interactions may exist that are not yet documented.
No listings found for P-21.
Related Compounds
View AllAdalank
Nootropic PeptidePreclinicalAdalank is a hybrid research peptide combining structural elements of Adamax (the adamantane-modified Semax analog) and Selank (the anxiolytic Pro-Gly-Pro tuftsin analog).
Adamax
Nootropic PeptidePreclinical / Research compoundAdamax is a synthetic nonapeptide (Ac-MEHFPGPAG-NH2) classified as a designer analog of Semax.
NA-Semax
Nootropic PeptidePreclinicalNA-Semax is the N-acetyl-l-aspartyl variant of Semax — the original ACTH(4-7) Pro-Gly-Pro analog developed at the Russian Academy of Sciences in the 1990s.
NA-Semax Amidate
Nootropic PeptidePreclinicalNA-Semax Amidate is the C-terminally amidated NA-Semax — the carboxylic acid at the peptide's C-terminus is replaced with an amide group (-NH2), which is reported to further extend metabolic half-life by resisting carboxypeptidase cleavage in addition to the aminopeptidase resistance the N-acetyl group already provides. The practical effect is a peptide with dosing-frequency leverage: where standard Semax often requires 3-4 daily doses to maintain effect, NA-Semax Amidate is reported (in vendor monographs and community usage) to maintain subjective effects on a 1-2x daily schedule.
P-21 Amidate
Nootropic PeptidePreclinicalP-21 Amidate is the amide-modified variant of P-21, the cyclic dipeptide derived from Selank.
Semax P-21
Nootropic PeptidePreclinicalSemax P-21 is a hybrid synthetic peptide combining structural motifs from Semax and P-21 into a single molecule.
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Protocols, calculator & safety for P-21
Research Score
4 PubMed studies
Quality Indicators
Data Completeness
75%Research Credibility
Limited research available
Quick Facts
Half-Life
~1-2 hours (cyclic peptides have substantially longer half-life than linear)
Molecular Weight
154.17 g/mol
Trial Phase
Preclinical
Safety Profile
Low RiskCommon Side Effects
- • Mild fatigue at start
Stop Use If
- Pregnancy/lactation
- Active depression on SSRIs (consult clinician)
- Peptide allergy
Research Disclaimer
This information is for educational and research purposes only. Not intended as medical advice. Consult a healthcare professional before use.
Frequently Asked Questions
What is P-21 used for in research?
P-21 is a synthetic cyclic dipeptide — Cyclo(L-prolyl-glycine) — derived from the Selank/Semax C-terminal Pro-Gly-Pro motif. It was isolated and characterized by the Institute of Molecular Genetics at the Russian Academy of Sciences as a metabolic fragment of Selank, and shown in animal studies to recapitulate much of Selank's anxiolytic and nootropic profile in a smaller, more BBB-penetrant molecule.
Unlike linear peptides that require intranasal administration to bypass enzymatic degradation, P-21's cyclic structure confers oral bioavailability — a significant practical advantage. Reported research applications include stress-induced cognitive deficit reversal, anxiolytic effects without sedation, and acute neuroprotection in MCAO (middle cerebral artery occlusion) stroke models.
As of 2026, P-21 is not FDA-approved. The published literature is concentrated in Russian-language journals from the 2010s; English-language peer-reviewed studies are sparse.
What forms does P-21 come in?
P-21 is available in vials, capsules, and sprays forms.
How much does P-21 cost?
Pricing varies by vendor and form.
How do I compare P-21 vendors?
Compare prices, payment methods, shipping, and COA scores across 0 vendors.
Research Tools
Related Compounds
View AllAdalank
Nootropic PeptidePreclinicalAdalank is a hybrid research peptide combining structural elements of Adamax (the adamantane-modified Semax analog) and Selank (the anxiolytic Pro-Gly-Pro tuftsin analog).
Adamax
Nootropic PeptidePreclinical / Research compoundAdamax is a synthetic nonapeptide (Ac-MEHFPGPAG-NH2) classified as a designer analog of Semax.
NA-Semax
Nootropic PeptidePreclinicalNA-Semax is the N-acetyl-l-aspartyl variant of Semax — the original ACTH(4-7) Pro-Gly-Pro analog developed at the Russian Academy of Sciences in the 1990s.
NA-Semax Amidate
Nootropic PeptidePreclinicalNA-Semax Amidate is the C-terminally amidated NA-Semax — the carboxylic acid at the peptide's C-terminus is replaced with an amide group (-NH2), which is reported to further extend metabolic half-life by resisting carboxypeptidase cleavage in addition to the aminopeptidase resistance the N-acetyl group already provides. The practical effect is a peptide with dosing-frequency leverage: where standard Semax often requires 3-4 daily doses to maintain effect, NA-Semax Amidate is reported (in vendor monographs and community usage) to maintain subjective effects on a 1-2x daily schedule.
P-21 Amidate
Nootropic PeptidePreclinicalP-21 Amidate is the amide-modified variant of P-21, the cyclic dipeptide derived from Selank.
Semax P-21
Nootropic PeptidePreclinicalSemax P-21 is a hybrid synthetic peptide combining structural motifs from Semax and P-21 into a single molecule.