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PeptideMostly animalNot FDA approved

P21

P021, a peptide mimetic of ciliary neurotrophic factor (CNTF)

Last reviewed October 27, 2026 · 14 sources · Written for general readers · Compare with another compound →

The bottom line

P21 is a small lab made peptide that helped memory and brain cell growth in Alzheimer model mice and old rats. Almost all of this work comes from the lab that created and patented it, and the one outside group that tested it in mice saw only limited benefit. It has never been tested in people, so its effects and side effects in humans are unknown.

Where the evidence stands

What it is

P21, also written P021, is a small lab made peptide based on the most active part of ciliary neurotrophic factor (CNTF), a natural protein that helps nerve cells survive.[1][2]

Its developers describe it as a chain of six building blocks, written Ac-DGGLAG-NH2. One unit carries an adamantyl group, a bulky ring shaped chemical meant to help it reach the brain and resist breakdown.[3] Because of this unusual building block, we do not list a standard formula or sequence.

Nearly all research on it comes from one research group in New York, whose senior scientist holds US patents on this family of CNTF based peptides.[1] A 2026 paper notes that several authors hold patents on P21 and that a cofounder is tied to a company licensed to develop it.[4]

Name
P21 (P021, a peptide mimetic of ciliary neurotrophic factor (CNTF))
Other names
P021
Type
Peptide

How it works

Lab and animal work suggests P21 acts on growth signals in the brain.

  • It blocks a signal called LIF that affects how brain stem cells develop, and it raises BDNF, a protein that helps nerve cells grow and survive.[1]
  • More BDNF turns down an enzyme called GSK-3β, which adds extra phosphate tags to tau, a protein that tangles in Alzheimer's disease.[1][5]
  • CNTF itself lasts only about 3 minutes in the blood, while P21 lasted more than 3 hours in testing.[1]
  • In rats, its developers report that it crosses from the blood into the brain when taken by mouth.[6]

All of this comes from rodent and lab work, almost entirely by the group that developed P21.

What the research shows

We keep animal and human evidence apart. A result in animals is a reason to study something in people, not proof that it works in people.

Animal and lab studies

Promising results in mice and rats, mostly from one lab

  • Normal adult mice given P21 learned faster, had better short term and spatial memory, and grew more new nerve cells in the hippocampus, a memory center of the brain.[3]
  • Old rats, 22 to 24 months of age, given P21 by mouth over a long period showed less age related loss of learning and memory, more BDNF and fewer lost nerve connections.[7] In old rats it also brought tau in spinal fluid back down to young adult levels.[6]
  • Female Alzheimer model mice fed P21 for 12 months starting in middle age had less abnormal tau and less soluble amyloid, and better memory. Plaque counts showed only a trend toward improvement.[5]
  • Starting P21 at 3 months of age, before disease appeared, prevented nerve cell loss, tau and amyloid buildup and memory problems in these mice, and fewer of them died.[8][2] Treating only from before birth until weaning also reduced later Alzheimer like changes.[12]
  • In a mouse model of Down syndrome, treatment from before birth through early life reduced developmental delay and adult memory problems.[10]
  • An Italian group tested P21 in mice lacking the CDKL5 gene, a rare childhood brain disorder. It helped nerve cells in a dish, but in the mice it did not raise BDNF or fix brain structure and gave only limited behavior benefit.[11]

Limit: Nearly all studies come from the group that created and patented P21, and the one outside test in mice was much less positive.[1][11]

Human studies

No human studies

  • We found no published study of P21 in people. Reviews by its developers in 2016 and 2022 describe only animal and cell work.[1][9]
  • No one has measured what people notice after taking it, how it affects memory in people, or what side effects it causes.[9]
  • Its parent protein, CNTF, was given to people in a trial for ALS (Lou Gehrig's disease) and caused loss of appetite, muscle loss, muscle pain and cramps, and extra sensitivity to pain. P21 is a much smaller molecule, and no one knows whether it shares these effects.[1]
  • The 2022 review notes that earlier trials of natural nerve growth proteins in people were stopped because the proteins did not reach the brain well, broke down fast or caused severe side effects. P21 was designed to avoid these problems, but this has not been tested in humans.[9]

Limit: No one knows what P21 does in people, good or bad.

Claims check

The most common claims about this compound, and what studies actually found. Verdicts rate the evidence, not whether you should use it.

Improves memory and learning

Only in animals

Memory gains have been shown only in rodents. Normal adult mice, old rats and several Alzheimer model mice did better on maze and object memory tests after P21.[3][7][5] No study has tested memory in people.

Grows new brain cells

Only in animals

In normal mice and in old rats, P21 increased the birth and maturing of new nerve cells in the hippocampus.[3][7] This has never been measured in people.

Prevents or treats Alzheimer's disease

Only in animals

In mice bred to develop Alzheimer like changes, P21 lowered abnormal tau and soluble amyloid and protected memory, with the best results when started early.[5][8] Plaques improved only slightly in one study.[5] No human trial has tested it in Alzheimer's disease.[9]

Reverses brain aging

Only in animals

In rats aged 22 to 24 months, long term P21 reduced age related memory decline and restored some nerve connections, and lowered tau in spinal fluid.[7][6] These results come from the developer's lab and have not been tested in older people.

Helps children's brain development disorders

Only in animals

In Down syndrome model mice, early P21 reduced developmental delay and memory problems.[10] In CDKL5 deficiency mice, a second research team that included the compound's developer found only limited behavior benefit and no change in brain structure.[11] No child or adult has been studied.

Has no side effects

Not tested

No human safety data exist. Its developers reported no side effects in mice treated for up to a year and no detectable immune reaction in rats.[1][6] Animal safety does not show safety in people, and its parent protein CNTF caused appetite and muscle loss in a human trial.[1]

Known risks and side effects

  • Untested in people. There are no human safety data at all. The only safety reports come from mice and rats studied by its developers.[1][6]
  • Parent protein side effects. CNTF caused appetite loss, muscle loss and pain in a human trial. Whether P21 does anything similar is unknown.[1]
  • One lab with patents. Almost all studies come from the group that owns patents on P21, and an outside mouse study found much weaker effects.[1][4][11]
  • Unregulated products. P21 is not on FDA's lists of substances nominated for compounding, so any product sold online has had no FDA check of identity, purity or strength.[13]
  • Sport rules. WADA does not name P21, but its S0 rule bans any drug with no government approval for human use.[14]

Regulatory status

Today: P21 has never been tested in people, so it is not an approved drug anywhere.[9] It does not appear on FDA's May 2026 list of substances nominated for compounding.[13] WADA's S0 rule bans unapproved drugs in sport.[14]

Sources

  1. Kazim SF, Iqbal K. Neurotrophic factor small-molecule mimetics mediated neuroregeneration and synaptic repair: emerging therapeutic modality for Alzheimer's disease. Mol Neurodegener. 2016;11(1):50. PMID 27400746
  2. Baazaoui N, Iqbal K. Prevention of dendritic and synaptic deficits and cognitive impairment with a neurotrophic compound. Alzheimers Res Ther. 2017;9(1):45. PMID 28655344
  3. Li B, Wanka L, Blanchard J, Liu F, Chohan MO, Iqbal K, et al. Neurotrophic peptides incorporating adamantane improve learning and memory, promote neurogenesis and synaptic plasticity in mice. FEBS Lett. 2010;584(15):3359-3365. PMID 20600002
  4. Falangola MF, Voltin J, Cole M, Nietert PJ, Liu F, Iqbal K, et al. Diffusion MRI measures detect brain microstructure changes due to early treatment with neurotrophic peptide mimetic P021 in the 3xTg-AD mouse model of Alzheimer's disease. Magn Reson Imaging. 2026;129:110641. PMID 41740658
  5. Kazim SF, Blanchard J, Dai CL, Tung YC, LaFerla FM, Iqbal IG, Iqbal K. Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease. Neurobiol Dis. 2014;71:110-130. PMID 25046994
  6. Khatoon S, Chalbot S, Bolognin S, Puoliväli J, Iqbal K. Elevated Tau Level in Aged Rat Cerebrospinal Fluid Reduced by Treatment with a Neurotrophic Compound. J Alzheimers Dis. 2015;47(3):557-564. PMID 26401692
  7. Bolognin S, Buffelli M, Puoliväli J, Iqbal K. Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound. Neurobiol Aging. 2014;35(9):2134-2146. PMID 24702821
  8. Baazaoui N, Iqbal K. Prevention of Amyloid-β and Tau Pathologies, Associated Neurodegeneration, and Cognitive Deficit by Early Treatment with a Neurotrophic Compound. J Alzheimers Dis. 2017;58(1):215-230. PMID 28387677
  9. Baazaoui N, Iqbal K. Alzheimer's Disease: Challenges and a Therapeutic Opportunity to Treat It with a Neurotrophic Compound. Biomolecules. 2022;12(10):1409. PMID 36291618
  10. Kazim SF, Blanchard J, Bianchi R, Iqbal K. Early neurotrophic pharmacotherapy rescues developmental delay and Alzheimer's-like memory deficits in the Ts65Dn mouse model of Down syndrome. Sci Rep. 2017;7:45561. PMID 28368015
  11. Mottolese N, Loi M, Trazzi S, Tassinari M, Uguagliati B, Candini G, et al. Effects of a ciliary neurotrophic factor (CNTF) small-molecule peptide mimetic in an in vitro and in vivo model of CDKL5 deficiency disorder. J Neurodev Disord. 2024;16(1):65. PMID 39592934
  12. Wei W, Wang Y, Liu Y, Dai CL, et al. Prenatal to early postnatal neurotrophic treatment prevents Alzheimer-like behavior and pathology in mice. Alzheimers Res Ther. 2020;12(1):102. PMID 32854771
  13. U.S. Food and Drug Administration. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (category lists). Updated May 14, 2026. FDA category list
  14. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. In force January 1, 2026. WADA 2026 List
Medical disclaimer

This page is educational information only. It is not medical advice and does not replace care from a licensed medical provider. Do not use this page to decide whether to take any substance. Talk to a licensed medical provider first.

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