# P21 — dosage, half-life & reference guide | PepVault

Source: https://pepvault.app/peptides/p21

Last updated: 2026-09-26

[Library](https://pepvault.app/peptides) [Cognitive](https://pepvault.app/peptides#cognitive) reviewed September 2026

# P21 Dosage, half-life & reference guide

Also known as CNTF analog · P-21 peptide

A peptide analog of CNTF (a nerve growth factor) that promoted neurogenesis and synaptic plasticity in mouse and rat studies from one lab. P21 is more stable than the parent protein and crosses the blood-brain barrier (shown with oral dosing in animals); in those studies it raised BDNF and improved memory.

- **Studied range:** 100–300 mcg
- **How often:** Daily
- **Half-life:** Unknown
- **Evidence:** Emerging
- **Route:** Intranasal

Studied in research — not a recommendation.

[P21 dose guide](https://pepvault.app/lab/dosage/p21)

## How it works.

Peptide analog of CNTF (Ciliary Neurotrophic Factor). Promoted neurogenesis, synaptic plasticity and memory in mouse and rat studies, and raised BDNF levels. More stable than CNTF itself and crosses the blood-brain barrier; the animal studies gave it by mouth, and nasal use is a community practice without published data.

**Commonly reported:** A subtle improvement in memory, recall and verbal fluency over a few weeks, and for many, little or no effect. No human data.

## Where P21 works.

- ### Brain, nerves & sleep

  **In animals.** Promoted neurogenesis, synaptic plasticity and memory in mouse and rat studies, and raised BDNF levels.

An area lights for what a peptide is used for and what people report, with the evidence beside it. It isn’t a promise that it works there.

## Week by week.

What to expect in the first 8 weeks

1. Day 1–14 Community

   ### Quiet onset by design

   Commonly reported: P21 is slow-acting, with no stimulant kick and no obvious day-one signal. It works through sustained BDNF elevation and downstream synaptic plasticity. Most users take it nasally, though the animal studies gave it by mouth.

   The science

   P21 is a CNTF peptide analog optimized for blood-brain barrier penetration and oral activity. Li et al. 2010 showed it boosted neurogenesis and memory in normal mice; Kazim et al. 2014 found higher BDNF in Alzheimer's-model mice. The developers report it works by blocking LIF signalling (a CNTF-family pathway) and raising BDNF.

   Sources

   - Li et al. (2010)
   - Kazim et al. (2014)

   Updated Sep 2026
2. Day 14–42 Community

   ### Memory and plasticity build

   Commonly reported by those who respond: better memory consolidation and learning speed, and a general sense of "the brain is working better", building cumulatively rather than dose-to-dose. Many notice little.

   The science

   In rodent studies, chronic oral dosing raised BDNF and hippocampal cell proliferation. Bolognin et al. 2014 found oral P21 reduced age-related memory decline in aged rats; Kazim et al. 2014 found benefits in Alzheimer's-model mice. Human pharmacokinetics are not characterized.

   Sources

   - Bolognin et al. (2014)
   - Kazim et al. (2014)

   Updated Sep 2026
3. Day 42–60 Community

   ### Cap the cycle and reassess

   Most community protocols cap at 4–6 weeks and then take a break, since no human dosing data exist. The animal studies dosed continuously for 1–12 months.

   The science

   Chronic use has not been characterized in humans. The 4–6 week cycle is community convention; the animal studies dosed continuously for 1 to 12 months without cycling.

   Sources

   - Kazim et al. (2014)

   Updated Sep 2026
4. Any day Animal

   ### What P21 is built on

   P21 has a strong mechanistic story (CNTF → BDNF → neurogenesis) and positive preclinical data in Alzheimer's models, nearly all from one lab. No human trials at all. Research-stage compound with a good science foundation and no clinical evidence.

   The science

   Developed by Iqbal's lab at the NY State Institute for Basic Research. Primary publications focus on Alzheimer's mouse models; the first P21 paper is Li et al. 2010, and Chohan et al. 2011 tested its 11-amino-acid parent, Peptide 6. The CNTF analog strategy avoids the toxicity and delivery issues that sank CNTF itself as a therapeutic candidate in the 1990s (ALS trials). No human trials.

   Sources

   - Li et al. (2010)
   - Kazim et al. (2014)
   - Bolognin et al. (2014)

   Updated Sep 2026

Day 1 is the day you start it.

## Mixing and a typical run.

Example numbers

### Reconstitution example

Reconstitute a 5 mg vial of P21 with 2 mL of bacteriostatic water and a 200 mcg dose is 8 units on a U-100 syringe, about 25 doses per vial.

- **Vial:** 5 mg
- **Water:** 2 mL
- **Amount:** 200 mcg

Draw to **8 units**

0.3 mL insulin syringe · 30 units

[Mix it in the Reconstitution Lab](https://pepvault.app/lab) [Open the calculator](https://pepvault.app/tools/reconstitution-calculator)

### Run notes

- **Cycle:** Very limited data. Short cycles of 4–6 weeks used cautiously. Community practice — opinions vary. Not a clinical recommendation.
- **Timing:** Intranasal. Timing not well established.
- **Route:** Intranasal
- **Stacks:** Dihexa, Semax

## Safety.

### Common side effects

- No human safety data
- Generally well tolerated
- Mild headache

## Goes with.

- [Dihexa](https://pepvault.app/peptides/dihexa)
- [Semax](https://pepvault.app/peptides/semax)

## Questions people ask.

### What is P21?

A peptide analog of CNTF (a nerve growth factor) that promoted neurogenesis and synaptic plasticity in mouse and rat studies from one lab. P21 is more stable than the parent protein and crosses the blood-brain barrier (shown with oral dosing in animals); in those studies it raised BDNF and improved memory.

### How is P21 dosed in research?

The research range for P21 is 100–300 mcg, daily. Studied in research — not a recommendation.

### How long does P21 last?

The half-life of P21 is unknown.

### What do people report on P21?

Commonly reported on P21: A subtle improvement in memory, recall and verbal fluency over a few weeks, and for many, little or no effect. No human data.

### Is P21 safe?

The research basis for P21 is emerging: primarily preclinical / limited human data. Common side effects in the library: no human safety data, generally well tolerated and mild headache.

### What does P21 stack with?

Common stacks for P21: Dihexa and Semax.

## Research.

The literature

### Search the latest research

[PubMed](https://pubmed.ncbi.nlm.nih.gov/?term=P21) [Google Scholar](https://scholar.google.com/scholar?q=P21)

## Reference.

- **Cadence:** Daily
- **Half-life:** Unknown
- **Research basis:** Emerging Primarily preclinical / limited human data

## More cognitive peptides

- [Cerebrolysin 5–10 ml](https://pepvault.app/peptides/cerebrolysin)
- [N-Acetyl Semax Amidate 100–600 mcg](https://pepvault.app/peptides/n-acetyl-semax-amidate)
- [Adamax No reference dose](https://pepvault.app/peptides/adamax)
- [Selank 250–500 mcg](https://pepvault.app/peptides/selank)
- [NSI-189 40–80 mg](https://pepvault.app/peptides/nsi-189)

## Free tools

- [P21 dose guide](https://pepvault.app/lab/dosage/p21)
- [Reconstitution Lab (3D)](https://pepvault.app/lab)
- [Peptide Sky (3D)](https://pepvault.app/lab/sky)
- [Peptide tier list](https://pepvault.app/lab/tiers)
- [Reconstitution calculator](https://pepvault.app/tools/reconstitution-calculator)
- [Half-life & active level](https://pepvault.app/tools/peptide-half-life-calculator)

PepVault for iPhone

## Track P21 in PepVault

Log every dose and keep your vial and the doses left in it. 7 days free on the yearly plan for new subscribers.

[Download on the App Store](https://apps.apple.com/app/apple-store/id6779318649?pt=129020030&ct=peptides-cta&mt=8)

[Open the calculator](https://pepvault.app/tools/reconstitution-calculator) [How the vial count works](https://pepvault.app/peptide-vial-tracker-app) [Explore the live demo](https://pepvault.app/login)

Reviewed September 2026 [How we check the library](https://pepvault.app/about#library)

PepVault is a research and tracking resource, not medical advice. Ranges are what studies used, never a dose for you. Brand names are trademarks of their owners; PepVault is independent of them.

PepVault is a private research and tracking tool, not medical advice. The information here is reference material from published literature and community use — always verify it and discuss any protocol with a qualified clinician before changing it.

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