P21 is a cognitive peptide used for brain / neurogenesis. P21 is a small peptide derived from CNTF, a natural nerve-growth factor. In plain terms: it is studied for growing new brain cells and protecting memory, but there is no human data.

How much water do I add to P21?

You can reconstitute P21 with 0.5, 1, or 2 mL of bacteriostatic water. Each option produces a different concentration and syringe draw for the same dose. Use the calculator to see which is easiest to measure.

What does P21 cost per dose?

Cost per dose depends on vial size, price paid, and your dose. Enter your vendor's price in the P21 calculator to see cost per dose and monthly cost.

What is the reference dose for P21?

The commonly referenced range is Research only, taken as studied. This is reference information, not a recommendation. Talk to a licensed clinician.

What are the side effects of P21?

Reported side effects of P21 include: There is no human data.. Severity and frequency vary by person and dose.

Who should not take P21?

P21 is generally not appropriate for: Pregnancy or breastfeeding; Active cancer, as a precaution with anything that promotes tissue or blood-vessel growth; Any prescription medicine you take regularly, without checking for interactions first; Anyone who wants established safety data, because none exists for this compound in humans. Talk to a licensed clinician before starting.

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Decoding

P21_Dosage, benefits & legal status

Also known as P021

By the Peptide Decoding Editorial Team

Published July 22, 2026 · Updated July 25, 2026

An experimental peptide studied for new brain cells and memory.

Brain / neurogenesisCognitive peptideResearch only

InBrain, mood and sleep

Common vial size5 mg

DoseResearch only

FrequencyAs studied

RouteUnder the skin (subcutaneous)

StatusResearch only

MixYour choice, calculate it

CycledNo established schedule

Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.

What is P21?

Plain language first. The technical label stays, but it never stands alone.

Overview

It is studied for growing new brain cells and protecting memory, but there is no human data.

The technical version

P21 is a small peptide derived from CNTF, a natural nerve-growth factor.

What it's used for

An experimental peptide studied for growing new brain cells and protecting memory.

How does P21 work?

What it does in the body, and where.

P21 is a small peptide derived from CNTF, a natural nerve growth factor, built to keep the growth-promoting activity while avoiding CNTF's side effects.

01
It mimics a nerve growth factor
Promoting the birth of new brain cells in the hippocampus, the region tied to memory formation.
02
Mouse results were positive
Including in Alzheimer's models, which is the source of the interest.
03
No human has ever taken it in a study
Confirmed by the Alzheimer's Drug Discovery Foundation. Everything claimed about it in people is extrapolation.

Pathway

A schematic of the compound's mechanism, not a diagnostic image.

What else is it used for?

Each use below carries its own evidence level. Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.

Growing new brain cells and protecting memoryResearch only

The published record

Research index

Records indexed for P21

2 in humans, 1 of them original studies.

Browse the records

In animalsPro

In the labPro

ReviewsPro

Senior author sharePro

Counted from Europe PMC indexing, not read by a person. Human means indexed under humans, which includes reviews and work on human cells. Original studies exclude reviews and lab work on human cells.Last updated 11 September 2026.

Compound field notes

At a glance

Four things to know about P21

Evidence

Research only

How much, and do you cycle it?

The range, and whether you take breaks.

Research only, as studied. No established scheduleNo range

No published study has established how long to take this or whether a break is needed. Schedules quoted online come from vendors and forums, and different sources disagree.

Compare this against the whole library →

How long does it stay in the body?

The half-life, and where the figure comes from.

Nothing publishedNo figure

Nothing published.

You can compare this against the whole library to see where it sits.

How do I dose and price it?

Enter your vial and your dose. Pick a mix. We show the draw and the cost.

The vial holds a fixed amount of drug. Adding more water does not make more drug, it just spreads it thinner, so you draw a bigger number on the syringe for the same dose.

Your vial size (mg)

Printed on the vial.

What you paid per vial

Used for cost per dose only.

Your dose (mg)

Commonly referenced range: Research onlyNo range

Choose your mix

0.5 mL water—units · 10 mg/mL

Half a 100-unit syringe

1 mL water—units · 5 mg/mL

One full 100-unit syringe

2 mL water—units · 2.5 mg/mL

Two full 100-unit syringes

your own mL

units · —

Enter your own volume

Measuring the water1 mL = one full 100-unit syringe.

Your draw

0 / 100 units

Full calculator with reorder date →Read a syringe →

What it costs

P21 starts at $39.00 across 13 vendors, typically $8.80 – $23.20 per mg.

15 listings, last read Sep 5, 2026. Shipping and card fees are not included.

See all 15 listings →

How do you store it?

Before mixing, and after.

Dry powder in the freezer or fridge. Once mixed, fridge, and use within about a month.

Unmixed lyophilized P21 keeps for a long time cold. Once you add water the clock starts: most reconstituted vials hold up for roughly 28 to 30 days at fridge temperature. Keep it out of light, and do not freeze it after mixing.

What are the side effects and cautions?

Known cautions and warnings for this compound.

Who should avoid it

Check these before anything else.

Pregnancy or breastfeeding
Active cancer, as a precaution with anything that promotes tissue or blood-vessel growth
Any prescription medicine you take regularly, without checking for interactions first
Anyone who wants established safety data, because none exists for this compound in humans

Stop and get help

These are emergencies. Seek care.

Spreading hives, swelling of the face or throat, or trouble breathing, which can happen with any injection and is a medical emergency
Redness, heat, or pus at the injection site, which can signal infection
Any severe or unexpected symptom
Anything unusual, since there is no known safety profile to compare it against

Common effects

Expected, and usually mild.

There is no human data.
Redness, soreness, or a small bump at the injection site
Beyond the above, unknown. There is no reliable human data on what this compound commonly causes

Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.

Is P21 approved?

And where the numbers on this page come from.

No. P21 is not approved for any use, anywhere. It is sold labelled for laboratory research only, and there is no legal route to buy it for human use.

Approval status
Research only
Route
Under the skin (subcutaneous)
Checked
July 2026

What has happened recently

We have not yet written a full regulatory note for this compound. The status above is current as of the date shown.

You can compare this against the whole library, or read how to check a seller.

DoseFrom research and community reports. No regulator has reviewed this dose.
Vial sizeFrom what vendors typically list; not a recommendation.
Sources
P021 in a cell and mouse model of CDKL5 deficiency disorder, Journal of Neurodevelopmental Disorders
Reviewed22 July 2026

What else is like P21?

Others in Brain, mood and sleep, side by side.

If you're weighing P21, it's worth reading PE-22-28, N-Acetyl Selank Amidate, and Noopept (Omberacetam) in the same class.

YOU ARE HERE

P21

An experimental peptide studied for new brain cells and memory.

Research only

Dose: Research only
How often: As studied

PE-22-28

An experimental fast-acting antidepressant peptide.

Research only

Dose: Research only
How often: As studied

NA-SELANK

N-Acetyl Selank Amidate

A longer-lasting version of Selank, with no study of its own.

Research only

Dose: Research only
How often: 1-2x daily

NOOPEPT

Noopept (Omberacetam)

A Russian memory drug sold as a supplement in the US, where selling it is unlawful.

Research only

Dose: 10 up to 30 mg per day (start low, increase slowly)
How often: 1-2x daily

Compare nootropic peptides

Guides for this compound

How to Reconstitute a Peptide
Mix peptide powder with bacteriostatic water, step by step.
How to Read an Insulin Syringe
Read the units, convert to millilitres, and draw the exact dose.
mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
How to Read a Peptide COA
What the purity number does and does not tell you, and how to spot an edited report.
How to Vet a Peptide Vendor
Independent COAs, HPLC purity, and the red flags that mean walk away.

Sources

P021 in a cell and mouse model of CDKL5 deficiency disorder, Journal of Neurodevelopmental Disorders(2024)
An independent group in Bologna, working with the peptide's originator, tested P021 (the compound sold as P21) in a second disease model. In cells it worked: proliferation, survival and neurite growth all recovered. In mice it mostly did not. Marble burying, nest building, limb clasping, rotarod, Morris water maze and passive avoidance were all unimproved, as were hippocampal neurogenesis, neuron survival and dendritic spine maturation. BDNF, the mechanism the compound is sold on, did not rise at either dose or age. Only the catalepsy bar test improved. Two routes were tried, oral at 60 nmol per gram of feed for 70 days from weaning and 750 nmol per mouse injected daily for 30 days in adults, with 4 to 9 mice per group.

Last reviewed 22 July 2026

Beyond these, 8 records are indexed. Browse the records