P21
Also known as: P021
P21 (also P021) is a small peptidergic compound — the tetrapeptide core Asp-Gly-Gly-Leu with an N-terminal acetyl and a C-terminal adamantylated glycine amide (Ac-DGGL(A)G-NH2) — derived from an active region (residues ~148–151) of human ciliary neurotrophic factor (CNTF). It was designed and characterized in the Khalid Iqbal laboratory at the New York State Institute for Basic Research in Developmental Disabilities (NYS IBR). It is an experimental, preclinical compound — NOT FDA-approved and NOT tested in humans in published trials. Distinct from the cyclin-dependent kinase inhibitor protein p21/CDKN1A/WAF1 (a completely different gene product; the two share only the name).
Who's worth your money for P21
Every current seller, ranked by independent evidence — Merit Score, latest COA purity, and live $/mg (size-normalized). Prices refresh daily. Rankings are never paid.
Top Merit pick
Highest Merit Score (88) of 3 scored sellers
$38.00 · 5mg
Best value
Lowest $/mg among scored sellers
$71.40 · 10mg · 98.6% purity
Average price
$13.64/mg
Sellers
12
45-day trend
-19%
11 of 12 sellers have a current price· 4 stale hidden· 4 unverified hidden
Top Merit pick
🇺🇸 Ruo Bio88✓ verified at source · just now
$7.60/mg -44.3% vs avg$38.00
5mg
no purity- 🇺🇸 Verified Peptides87
✓ verified at source · just now
$7.14/mg -47.7% vs avg$71.40
10mg
- 🇺🇸 Simple Peptide85
✓ verified at source · just now
$19.80/mg +45.2% vs avg$198
10mg
no purity
Prices observed from public storefronts (last 24h), normalized to $/mg. "Evidence" is Merit's 0–100 Merit Score, derived only from observable verification evidence (methodology on /about); "Purity" is the latest independent COA. Some buy links are affiliate links — Merit may earn a commission at no extra cost to you, and where a vendor offers one, the code shown gets you a discount at their checkout. Affiliate status never affects price data, ranking, or the Merit Score (full policy on /disclosure). Research use only.
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About P21
CAS
1246751-68-7
Molecular formula
C27H42N6O8
Sequence
DGGL
Typical dose range
500–750 mcg/day intranasal (research use); 250–1000 mcg/day range reported
Half-life
>6 hours (rodent; estimated, based on parent Peptide 6 and adamantane-modified stability)
COAs for P21
4 third-party tests across 2 vendors. Each card links to the full report.
For
P-21
by Verified Peptides· batch P2106260210B
For
P-21
by Skye Peptides· batch P2125-10-001
Purity not on file
For
P21
by Skye Peptides· batch P2125-10-001
Purity not on file
For
P21
by Skye Peptides· batch P2125-10-001
20 citations indexed for P21
review · 2026
Exercise and p21 signaling in central nervous system aging and senescence: A context- and dose-dependent relationship
Physical exercise is a potent modifier of CNS aging, but its relationship with the cyclin-dependent kinase inhibitor p21 (CDKN1A) is neither uniformly suppressive nor equivalent to cellular senescence. Direct evidence remains sparse and preclinical.
Study · 2026
p21 (CDKN1A) Is the Major Driver of Sulforaphane-Mediated Reduction in SAMHD1 T592 Phosphorylation in Macrophages
Sulforaphane (SFN), a natural compound found in cruciferous vegetables, mobilizes the transcription factor NRF2 to protect macrophages from HIV-1. SFN/NRF2 exerts this protective effect by promoting the reduced phosphorylation of the antiviral protein SAMHD1.
animal · 2026
p21 Inhibition Rescues Radiation-Induced Osteogenic Dysfunction and Promotes Bone Regeneration in Osteoradionecrosis of the Jaw via the Rb-Smad2/3-Runx2 Axis
Background Osteoradionecrosis of the jaw (ORNJ) is a severe radiotherapy complication with unclear molecular drivers. CDKN1A/p21 is upregulated by radiation-induced DNA damage, but its role in ORNJ remains unknown. Methods An ORNJ mouse model was established.
animal · 2026
Hyperexcitability in hippocampal CA1 pyramidal cells of Fmr1 knockout mice emerges during late postnatal development
Fragile X syndrome (FXS) is a neurodevelopmental disorder and the most frequent monogenic form of intellectual disability and autism. Fmr1 knockout (KO) mice have been used to study the neuronal bases of FXS.
Study · 2026
Senescence Markers and Associated Transcriptomic Changes Are Expressed at Early Stages of Alzheimer's Neuropathology but Are Not Independently Related to Dementia
Cellular senescence may affect the post-mitotic cells of the brain.
animal · 2026
Hepatic Cellular Senescence Is Attenuated by Filbertone via Modulation of the p53-p21 Pathway in AML12 Hepatocytes
Background/Objectives : Cellular senescence refers to a state where the phenotype of cells changes, and the cell cycle comes to a halt. Cellular aging occurs due to various causes and is implicated in the development of various age-related diseases.