P21 peptide (P021)

Summary

P21 (P021) is a small synthetic peptide designed at the New York State Institute for Basic Research to mimic a fragment of ciliary neurotrophic factor (CNTF), a protein that supports nerve cell survival. In mice it improves learning and memory, increases hippocampal neurogenesis (new nerve cells in the brain's memory center), and in a triple transgenic Alzheimer model (mice bred to develop Alzheimer-like disease) reduces tau hyperphosphorylation, the protein change behind Alzheimer tangles, but no human trial or safety study has ever been published, so its evidence grade is animal-only. It has never been reviewed by FDA, is not on any 503A compounding list (FDA's lists of ingredients pharmacies may use), and is prohibited in sport under WADA section S0, the anti-doping ban on unapproved substances.

What is P21?

P21 is a synthetic adamantane-modified tetrapeptide derived from the active region of ciliary neurotrophic factor (CNTF). It is also known as P021, Ac-DGGLAG-NH2, CNTF peptide mimetic, Peptide 021, P21 peptide, P021 peptide.

How does it work?

P21 is proposed to act as a CNTF mimetic that inhibits leukemia inhibitory factor (LIF) signaling and increases brain-derived neurotrophic factor (BDNF) expression, which in turn promotes neurogenesis, neuronal maturation, and synaptic plasticity in the dentate gyrus. In the 3xTg-AD mouse it also reduced abnormal tau phosphorylation and soluble amyloid beta, an effect the authors attributed to increased BDNF activity. The adamantane modification was added to improve blood brain barrier penetration and oral stability. All of this comes from rodent and cell work.

What does the evidence say about P21?

Evidence consists of rodent studies from a single research group. Peripheral P21 improved short-term and spatial memory and increased dentate gyrus neurogenesis in normal adult mice (2010). Twelve months of oral P021 in 3xTg-AD mice starting at 9 to 10 months of age reduced tau pathology, lowered soluble amyloid beta, and rescued cognition, neurogenesis, and synaptic plasticity (2014). Later work reported effects in aged rats and mouse models of retinal degeneration and early development. No independent replication and no human data have been published.

Human evidence

No human study of P21 has been published. No clinical trial registration, pharmacokinetic study, or safety report in humans was identified as of the last verification date.

Animal evidence

In normal C57BL/6 mice, peripheral P21 enhanced learning, short-term memory, and spatial reference memory and increased neurogenesis and maturation of newborn neurons in the dentate gyrus. In female 3xTg-AD mice fed P021 in the diet for 12 months, tau hyperphosphorylation at Alzheimer associated sites and soluble amyloid beta were reduced, and deficits in cognition, neurogenesis, and synaptic plasticity were rescued. Chronic treatment was described as well tolerated in mice, but formal toxicology has not been published.

Key studies

Conditions studied

Is P21 legal in the United States?

FDA and compounding status

P21 has never been nominated to or reviewed for the FDA 503A or 503B bulks lists and does not appear in any category on the FDA Category 2 page (current as of April 22, 2026). It is not a component of any approved drug, so a 503A pharmacy has no lawful basis to compound it. It is not an FDA approved drug.

WADA status

WADA prohibited. Athletes subject to anti-doping testing should treat this as prohibited at all times unless the current prohibited list says otherwise.

Regulatory timeline

No regulatory events recorded.

Full tracker for P21 or the category-wide tracker.

What published studies of P21 used

Ranges below are reported from published studies and labeling only. PeptideAgent does not recommend doses or protocols.

Not established in human literature. Mouse studies delivered P021 orally in the diet or by peripheral injection at research doses that have no established human equivalent.

Routes reported

What are the side effects and interactions of P21?

Side effects

Interactions

Contraindications

How do people access P21 legally?

Typical cost: Not available through licensed channels. Research chemical sellers list it, but those products are not lawful for human use and are not verified for identity or purity.

• Rules by state
• Verified provider directory

Compare P21

• P21 vs Dihexa

What's actually offered, and what that means for you

Licensed compounding pharmacies, clinics, and telehealth prescribers openly offer many unapproved peptides, and prescribers write prescriptions for them. That does not make P21 lawful. P21 is not FDA approved and not on the 503A bulks list, so a pharmacy has no lawful basis to compound it. [4] [7]

Enforcement is uneven. FDA mostly acts through warning letters to compounders and online sellers, Category 2 safety listings, and import alerts that let it detain shipments, rather than stopping every pharmacy. State pharmacy boards oversee pharmacies day to day, and their rules differ. [4] [5] [8] [9] [10]

What changes for you

• No FDA review of the product: FDA does not check a compounded drug's safety, effectiveness, or quality before it is sold. [5]
• Identity, purity, sterility, and dose accuracy can vary from batch to batch. [4]
• Insurance rarely covers it, so you usually pay cash.
• For tested athletes, P21 is prohibited at all times on the WADA list, whatever the source. [6]

What to check

These checks lower some risks, but they do not make an unlawfully compounded product lawful or safe. Check for:

• A 503A pharmacy licensed in your state (your state board of pharmacy publishes license lookups). [5]
• A real evaluation by a licensed prescriber, not just an online form.
• A certificate of analysis for the specific batch.

Frequently asked questions

Decisions about starting, stopping, or combining any treatment belong with a licensed clinician who knows your history.

Sources

Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.