P21 Peptide: What It Is and What the Research Shows
P21 peptide usually means P021, a lab-made research peptide (Ac-DGGLAG-NH2) taken from ciliary neurotrophic factor (CNTF). It is not the same as p21 (CDKN1A), a natural protein that stops the cell cycle after DNA damage. In Alzheimer model mice fed P021 for 12 months, it rescued problems in memory, new neuron growth and synapse function. No human study of P021 was found.
Sources: Animal study (mice). Wei W et al. Neurotrophic Treatment Initiated During Early Postnatal Development Prevents the Alzheimer-Like Behavior and Synaptic Dysfunction. Journal of Alzheimer's Disease, 2021. PMID 34057082. Supports: P021 is the CNTF-derived peptide Ac-DGGLAG-NH2; Animal study (mice). Kazim SF et al. Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease. Neurobiology of Disease, November 2014. PMID 25046994. Supports: 12 months of P021 diet in female 3xTg-AD mice; cognition, neurogenesis, synaptic plasticity and tau results; Review. Ticli G et al. Revisiting the Function of p21(CDKN1A) in DNA Repair: The Influence of Protein Interactions and Stability. International Journal of Molecular Sciences, 24 June 2022. PMID 35806061. Supports: p21 protein as a cyclin-dependent kinase inhibitor, cell cycle arrest, DNA repair and replication speed
Short answer
- Which p21 is the peptide?
- If you saw p21 called a peptide, it usually means P021, a six amino acid research peptide studied for memory in mice and rats.
- And the other p21?
- In biology papers, p21 is the CDKN1A protein. Your cells make it to pause division after DNA damage. It is a different molecule.
- What has P021 shown?
- Better memory and more new neurons in mice and old rats. A 2016 review calls the evidence preclinical.
- Has it been tested in people?
- No human study of P021 was found in PubMed or ClinicalTrials.gov.
Sources: Animal study (rats). Bolognin S et al. Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound. Neurobiology of Aging, September 2014. PMID 24702821. Supports: reduced age-related learning and memory decline in 22 to 24 month old rats; Review. Kazim SF et al. Neurotrophic factor small-molecule mimetics mediated neuroregeneration and synaptic repair: emerging therapeutic modality for Alzheimer's disease. Molecular Neurodegeneration, 11 July 2016. PMID 27400746. Supports: how P021 is reported to act (LIF, BDNF, dentate gyrus), blood-brain barrier and oral dosing claims, evidence called preclinical; Review. Ticli G et al. Revisiting the Function of p21(CDKN1A) in DNA Repair: The Influence of Protein Interactions and Stability. International Journal of Molecular Sciences, 24 June 2022. PMID 35806061. Supports: p21 protein as a cyclin-dependent kinase inhibitor, cell cycle arrest, DNA repair and replication speed
Two Different Things Called p21
Search results mix up a peptide and a protein that share a name. The table sets them side by side so you can tell which one a source is talking about.
| Feature | P021 (the peptide) | p21 (the protein) |
|---|---|---|
| What it is | A lab-made six amino acid peptide, Ac-DGGLAG-NH2 | A natural protein made by your cells |
| Where it comes from | A piece of ciliary neurotrophic factor (CNTF) | The CDKN1A gene |
| Main job reported | More new neurons and better memory processes in animals | Stops the cell cycle after DNA damage |
| Kind of evidence | Mice and rats only (preclinical) | Cell biology reviews on DNA repair and metabolism |
| Link to aging | Reduced age-related learning decline in old rats | Links DNA damage to senescence |
Sources: Animal study (mice). Wei W et al. Neurotrophic Treatment Initiated During Early Postnatal Development Prevents the Alzheimer-Like Behavior and Synaptic Dysfunction. Journal of Alzheimer's Disease, 2021. PMID 34057082. Supports: P021 is the CNTF-derived peptide Ac-DGGLAG-NH2; Review. Kazim SF et al. Neurotrophic factor small-molecule mimetics mediated neuroregeneration and synaptic repair: emerging therapeutic modality for Alzheimer's disease. Molecular Neurodegeneration, 11 July 2016. PMID 27400746. Supports: how P021 is reported to act (LIF, BDNF, dentate gyrus), blood-brain barrier and oral dosing claims, evidence called preclinical; Review. Ticli G et al. Revisiting the Function of p21(CDKN1A) in DNA Repair: The Influence of Protein Interactions and Stability. International Journal of Molecular Sciences, 24 June 2022. PMID 35806061. Supports: p21 protein as a cyclin-dependent kinase inhibitor, cell cycle arrest, DNA repair and replication speed; Review. Elmitwalli O et al. The Emerging Role of p21 in Diabetes and Related Metabolic Disorders. International Journal of Molecular Sciences, 9 December 2024. PMID 39684919. Supports: p21 links DNA damage to apoptosis, senescence and cell cycle arrest
What Peptide Is P21?
P21 is P021, also written Peptide 021. It is a short peptide, Ac-DGGLAG-NH2. It is made from a piece of ciliary neurotrophic factor (CNTF), a natural growth factor for nerve cells.
A 2016 review describes P021 as neurogenic and neurotrophic. In plain words, it is reported to help new neurons form and to support nerve cells. The review says it acts in a brain region called the dentate gyrus. It blocks a signal called leukemia inhibitory factor (LIF). It also raises brain-derived neurotrophic factor (BDNF).
The same review says P021 is small and crosses the blood-brain barrier. It says P021 suits oral dosing and lacks the side effects linked to natural CNTF or BDNF. Those points come from animal work, and the review calls the evidence preclinical. For other compounds studied for the brain, see peptides for brain function.
Sources: Animal study (mice). Wei W et al. Neurotrophic Treatment Initiated During Early Postnatal Development Prevents the Alzheimer-Like Behavior and Synaptic Dysfunction. Journal of Alzheimer's Disease, 2021. PMID 34057082. Supports: P021 is the CNTF-derived peptide Ac-DGGLAG-NH2; Review. Kazim SF et al. Neurotrophic factor small-molecule mimetics mediated neuroregeneration and synaptic repair: emerging therapeutic modality for Alzheimer's disease. Molecular Neurodegeneration, 11 July 2016. PMID 27400746. Supports: how P021 is reported to act (LIF, BDNF, dentate gyrus), blood-brain barrier and oral dosing claims, evidence called preclinical
The P021 Mouse and Rat Studies
Three animal models carry most of the P021 story: Alzheimer model mice, old rats and a mouse model of Down syndrome.
- Alzheimer model mice (2014): female 3xTg-AD mice got P021 in their diet for 12 months, starting at 9 to 10 months old. P021 rescued problems in cognition, new neuron growth and synapse plasticity. The study also saw a significant drop in abnormal tau build-up, a hallmark of Alzheimer disease.
- Old rats (2014): in 22 to 24 month old Fisher rats, P021 significantly reduced the age-related decline in learning and memory.
- Down syndrome model mice (2017): in Ts65Dn mice, early P021 treatment rescued developmental delay in pups and Alzheimer-like memory problems in adult life.
These are animal results. The 12 month diet above is a feeding schedule for mice, not a human dose. No human dose was found.
Sources: Animal study (mice). Kazim SF et al. Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease. Neurobiology of Disease, November 2014. PMID 25046994. Supports: 12 months of P021 diet in female 3xTg-AD mice; cognition, neurogenesis, synaptic plasticity and tau results; Animal study (rats). Bolognin S et al. Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound. Neurobiology of Aging, September 2014. PMID 24702821. Supports: reduced age-related learning and memory decline in 22 to 24 month old rats; Animal study (mice). Kazim SF et al. Early neurotrophic pharmacotherapy rescues developmental delay and Alzheimer's-like memory deficits in the Ts65Dn mouse model of Down syndrome. Scientific Reports, 3 April 2017. PMID 28368015. Supports: Down syndrome model mouse results
What Does the p21 Protein Do?
The p21 protein, also called CDKN1A, mainly controls the cell cycle. It is a cyclin-dependent kinase inhibitor, which means it can stop a cell from dividing after its DNA is damaged.
It does more than hit pause. p21 links DNA damage to cell processes including cell cycle arrest, cell death (apoptosis) and senescence. It is also needed to repair several types of DNA damage well. And it affects how fast DNA is copied. If senescence is your interest, see our guide to FOXO4-DRI, a peptide studied for clearing senescent cells.
Sources: Review. Ticli G et al. Revisiting the Function of p21(CDKN1A) in DNA Repair: The Influence of Protein Interactions and Stability. International Journal of Molecular Sciences, 24 June 2022. PMID 35806061. Supports: p21 protein as a cyclin-dependent kinase inhibitor, cell cycle arrest, DNA repair and replication speed; Review. Elmitwalli O et al. The Emerging Role of p21 in Diabetes and Related Metabolic Disorders. International Journal of Molecular Sciences, 9 December 2024. PMID 39684919. Supports: p21 links DNA damage to apoptosis, senescence and cell cycle arrest
What P021 Improved in Mice and Rats
P021 improved memory and new neuron growth, and lowered tau build-up, in mice and rats. None of these benefits has been tested in people.
- Memory and learning: better in Alzheimer model mice, Down syndrome model mice and old rats.
- New neurons: more neuron growth in Alzheimer model mice.
- Tau build-up: lower in Alzheimer model mice.
- Anti-aging in people: not tested. The only aging result is less age-related learning decline in old rats.
Sources: Animal study (mice). Kazim SF et al. Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease. Neurobiology of Disease, November 2014. PMID 25046994. Supports: 12 months of P021 diet in female 3xTg-AD mice; cognition, neurogenesis, synaptic plasticity and tau results; Animal study (rats). Bolognin S et al. Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound. Neurobiology of Aging, September 2014. PMID 24702821. Supports: reduced age-related learning and memory decline in 22 to 24 month old rats; Animal study (mice). Kazim SF et al. Early neurotrophic pharmacotherapy rescues developmental delay and Alzheimer's-like memory deficits in the Ts65Dn mouse model of Down syndrome. Scientific Reports, 3 April 2017. PMID 28368015. Supports: Down syndrome model mouse results
How P021 Was Given in the Studies, and What Is Known About Safety
In the main Alzheimer mouse study, P021 was mixed into the mice's food for 12 months. No human dose exists, and its safety in people is unknown.
The 2016 review describes P021 as suited to this. It says P021 is small, crosses the blood-brain barrier and suits oral dosing. It also says P021 lacks the side effects linked to natural CNTF or BDNF. Both points come from animal work. No human study or FDA label for P021 was found.
Sources: Animal study (mice). Kazim SF et al. Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease. Neurobiology of Disease, November 2014. PMID 25046994. Supports: 12 months of P021 diet in female 3xTg-AD mice; cognition, neurogenesis, synaptic plasticity and tau results; Review. Kazim SF et al. Neurotrophic factor small-molecule mimetics mediated neuroregeneration and synaptic repair: emerging therapeutic modality for Alzheimer's disease. Molecular Neurodegeneration, 11 July 2016. PMID 27400746. Supports: how P021 is reported to act (LIF, BDNF, dentate gyrus), blood-brain barrier and oral dosing claims, evidence called preclinical
Is p21 Good or Bad?
It depends which p21 you mean, and neither fits a simple label. The p21 protein is a normal guard of the genome that also pushes damaged cells into arrest, death or senescence. The P021 peptide has shown benefits only in mice and rats. Its safety and effects in people are unknown, and no FDA label for it was found.
Sources: Review. Ticli G et al. Revisiting the Function of p21(CDKN1A) in DNA Repair: The Influence of Protein Interactions and Stability. International Journal of Molecular Sciences, 24 June 2022. PMID 35806061. Supports: p21 protein as a cyclin-dependent kinase inhibitor, cell cycle arrest, DNA repair and replication speed; Review. Elmitwalli O et al. The Emerging Role of p21 in Diabetes and Related Metabolic Disorders. International Journal of Molecular Sciences, 9 December 2024. PMID 39684919. Supports: p21 links DNA damage to apoptosis, senescence and cell cycle arrest; Review. Kazim SF et al. Neurotrophic factor small-molecule mimetics mediated neuroregeneration and synaptic repair: emerging therapeutic modality for Alzheimer's disease. Molecular Neurodegeneration, 11 July 2016. PMID 27400746. Supports: how P021 is reported to act (LIF, BDNF, dentate gyrus), blood-brain barrier and oral dosing claims, evidence called preclinical
Common Questions
What peptide is p21?+
When people say p21 peptide, they usually mean P021 (Peptide 021). P021 is a short lab-made peptide, Ac-DGGLAG-NH2, derived from a piece of ciliary neurotrophic factor (CNTF). It is not the same as p21, the natural cell cycle protein also called CDKN1A.
What are the benefits of the p21 peptide?+
Only animal benefits have been reported. In Alzheimer model mice, P021 rescued problems in cognition, new neuron growth and synapse function. In 22 to 24 month old rats it reduced the age-related decline in learning and memory. No human study of P021 was found.
What does p21 do?+
The p21 protein mainly controls the cell cycle. It links DNA damage to cell cycle arrest, cell death and senescence, and it is needed for efficient repair of several kinds of DNA damage. The P021 peptide is a different thing: it is reported to boost new neuron growth and memory in animals.
What is the function of the p21 protein in normal cells?+
In normal cells, p21 helps keep the genome stable. It works as a cyclin-dependent kinase inhibitor, which stops the cell cycle after DNA damage. It also helps repair DNA and affects how fast DNA is copied.
Is p21 good or bad?+
Neither, as a simple label. The p21 protein is a normal part of how cells protect their DNA, and it also steers damaged cells toward arrest, death or senescence. The P021 peptide has shown benefits only in mice and rats, and its effects in people are unknown.
Where can I buy p21 peptide for sale?+
P021 is not an approved medicine, and this page does not point to sellers. All published P021 research found is in mice, rats or cells, and no FDA label or human safety data were found.
Sources: Animal study (mice). Wei W et al. Neurotrophic Treatment Initiated During Early Postnatal Development Prevents the Alzheimer-Like Behavior and Synaptic Dysfunction. Journal of Alzheimer's Disease, 2021. PMID 34057082. Supports: P021 is the CNTF-derived peptide Ac-DGGLAG-NH2; Animal study (mice). Kazim SF et al. Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease. Neurobiology of Disease, November 2014. PMID 25046994. Supports: 12 months of P021 diet in female 3xTg-AD mice; cognition, neurogenesis, synaptic plasticity and tau results; Animal study (rats). Bolognin S et al. Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound. Neurobiology of Aging, September 2014. PMID 24702821. Supports: reduced age-related learning and memory decline in 22 to 24 month old rats; Review. Ticli G et al. Revisiting the Function of p21(CDKN1A) in DNA Repair: The Influence of Protein Interactions and Stability. International Journal of Molecular Sciences, 24 June 2022. PMID 35806061. Supports: p21 protein as a cyclin-dependent kinase inhibitor, cell cycle arrest, DNA repair and replication speed; Review. Elmitwalli O et al. The Emerging Role of p21 in Diabetes and Related Metabolic Disorders. International Journal of Molecular Sciences, 9 December 2024. PMID 39684919. Supports: p21 links DNA damage to apoptosis, senescence and cell cycle arrest
Related reading
This guide is for educational purposes only and is not medical advice. It describes what published mouse, rat and cell biology research reports about the P021 peptide and the p21 protein. It is not an endorsement or an instruction to use any compound. P021 is a research compound that is not approved for human use. Talk to a qualified healthcare professional before making any decision about your health.