P21

P21 is a synthetic CNTF‑derived peptide that researchers and biohackers use primarily for cognitive enhancement and memory improvement, based on its studied effects on hippocampal neurogenesis. In the community the typical regimen is 4 mg per day, with doses reported anywhere from 500 µg up to 4 mg; users rarely specify timing or cycling, so schedules are generally left open. The main limitation is that the off‑label evidence base is thin, with most exploratory indications lacking posted results, and injection‑site reactions are occasionally reported, while other side effects have not been consistently observed.

Half-life~4 h

Data last updated

ClinicalResearchDepthClinicalResearchEfficacyClinicalResearchSideEffectsno dataAnecdotalEfficacyAnecdotalSideEffectsPrice1.51.73.43.12.0

Measured on 5 of 6 axes

Research Evidence

Evidence shape

P21 currently sits at a low evidence tier, as there are no published human studies to support its use. The existing research is restricted to preclinical models and a single completed trial for idiopathic thrombocytopenic purpura, which remains the only registered human data point. Because this evidence is limited to a solitary, early-stage trial and foundational animal research, the clinical profile of P21 lacks the breadth and replication required to establish efficacy or safety in human populations.

Depthhow much
1 registered trial
1 completed
Breadthhow many areas
2 indications mapped
1 thin / exploratory · 1 animal-only · 1 single-trial long-tail
Qualityhow rigorous
Highest tier: Phase 1
Breadth and depth20 rows captured
Human
direct clinical signal
1
Animal
translational support
7
In vitro
mechanistic support
12
HighMediumLow

Anecdotal efficacy

P21 side effects

Clinical research side effects

Clinical safety table not projected yet.

Anecdotal side effects

Price

Full buying guide →
1
Top Peptide
--
50 mg
$65.99
$1.32/mg
2
Elite Aminos LLC
--
30 mg
$55.00
$1.83/mg
3
Purerxpeptides
US
30 mg
$55.00
$1.83/mg
4
Bluum Peptides
--
10 mg
$39.00
$3.9/mg
5
Raccoon Peptides
GB
10 mg
$40.13
$4.01/mg
6
OP Labs
United Kingdom
5 mg
$30.74
$6.15/mg

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P21 dosing & protocol

How P21 is dosed across research, clinician, and community sources — each evidence tier kept separate so the dose range, frequency, timing, and cycling stay visible without flattening different levels of evidence.

Research trials
Published clinical-trial protocols · n = 1
Typical dose
10 mg
typical
0
2 mg
4 mg
6 mg
8 mg
10 mg
single reported dose
Route
oral

One trial used 10 mg taken orally, from a single registered study.

1 source
Clinician practice
Doctor & published-protocol guidance
Typical dose
—
0
2 mg
4 mg
6 mg
8 mg
10 mg
no dose captured for this tier yet

No structured protocol details captured for this tier yet.

Anecdotal
Community-reported real-world use · n = 4
Typical dose
4 mg500 µg – 4 mg
typical
0
2 mg
4 mg
6 mg
8 mg
10 mg
distribution of 4 reported doses · darker = more
Frequency
unspecified
Route
subQ

Across four community reports, doses span 0.5 mg to 4 mg subQ; two of the four specified daily administration, while the others noted a dose without a cadence, and no cycling patterns were reported.

4 sources

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