A to Z / Cognitive

P21

Also known as P021, CNTF-derived peptide.

Best known for The neurogenesis peptide from Alzheimer's research

Evidence★☆☆☆☆

Safety dataLargely unknown

Route Oral · nasal

United StatesNot approved

AustraliaNot listed by name; unapproved therapeutic good

as at 16 September 2026

What it is and what it does

P21 is a small peptide derived from ciliary neurotrophic factor (CNTF), developed in academic Alzheimer's research. The work so far is in animal models, with no human trials yet, and it is not approved. It is commonly discussed as a nootropic for memory and neurogenesis.

A naming note: P21 is also the name of an entirely unrelated and important cell-cycle protein (p21/CDKN1A). Search results often mix the two up, and material about the cell-cycle protein does not relate to this compound.

What the full entry covers

The book carries the rest of this entry:

Where the research stands, with every claim cited
What people commonly ask, and what the research shows so far
Dosing in four labelled bands, described and not recommended
Side effects, serious risks, cautions and interactions
Questions to discuss with your doctor
How it compares with Dihexa, Semax, Cerebrolysin, Davunetide

Related entries

DihexaThe Alzheimer's research peptide at an early stage of study · Evidence ★☆☆☆☆
SemaxThe leading nootropic peptide · Evidence ★★☆☆☆
CerebrolysinThe brain peptide mixture used clinically outside the West · Evidence ★★★☆☆
DavunetideThe neuroprotective peptide that reached a phase 2/3 trial, and what its results teach · Evidence ★★★☆☆

A certificate of analysis tells you what is in a vial. The evidence rating above tells you whether the compound has been shown to work in humans. Neither answers the other's question. How to read a certificate of analysis.

This page describes what is known and not known about P21. It is not medical advice and not a recommendation to use it.