P21
Synthetic hexapeptide derived from CNTF (ciliary neurotrophic factor)
- Class
- Nootropic peptide
- Half-life
- ~10 min
- Route
- Intranasal
- Cadence
- Daily
- Evidence
- Animal data primarily
Overview
P21 is a synthetic six-amino-acid peptide (Ac-DGGL(A)G-NH2) designed as a short, stable fragment derived from ciliary neurotrophic factor (CNTF). The original rationale: CNTF promotes neuron survival and synaptic plasticity in animal models, but it's a large protein that doesn't cross the blood-brain barrier well and triggers harsh side effects when given systemically. P21 was engineered to retain some of CNTF's neurotrophic effects in a smaller, intranasal-deliverable package.
The peptide appears in research-market catalogues as a nootropic, with sellers claiming it enhances memory, learning, and neuroplasticity. The evidence base is almost entirely rodent studies — mostly Russian-language publications from the 2000s-2010s showing improved performance in Morris water maze and passive avoidance tests after intranasal dosing. There are no published human trials, no FDA/EMA regulatory filings, and no independent Western replications of the original Russian data.
Bottom line: P21 is a real peptide sequence with some published animal data supporting a cognitive effect, but the human evidence is zero and the animal data comes from a narrow source base. It's in a grey zone between 'legitimate research peptide with thin data' and 'research-market product with no real clinical grounding.'
Update: As of 2026, one Phase I safety trial has been completed — 22 patients received P21 via intravitreal injection for diabetic retinopathy, with Phase II efficacy trials now ongoing. This is the first published human data, but it uses an ophthalmic delivery route (intravitreal) rather than the intranasal route studied in animal cognitive research. Human safety and efficacy data for intranasal cognitive use remain absent.
Safety considerations
A few of the safety signals worth knowing — the full list, with dosing context and what to monitor, is inside AIx Core.
- Not approved for human use by any regulator. No human safety trials published. All efficacy data are rodent-only.
- No long-term toxicity studies in any species. The safety profile beyond 2-4 weeks of daily dosing is completely unknown.
- Intranasal delivery bypasses the blood-brain barrier — this is the intended mechanism, but it also means systemic safety checks (liver metabolism, renal clearance) don't apply in the usual way. Unknown CNS accumulation risk.
+ 4 more safety notes inside AIx Core →
Commonly monitored
Markers and signals people track when researching P21.
- Subjective cognitive changes — memory, focus, learning speed
- Sleep quality (some users report vivid dreams or disrupted sleep)
- Mood — irritability or anxiety if dosing too high
- Nasal irritation or congestion from intranasal delivery
- Neurological symptoms — headache, dizziness, any unusual sensory changes
Frequently asked questions
What is P21?
Synthetic hexapeptide derived from CNTF (ciliary neurotrophic factor). P21 is a synthetic six-amino-acid peptide (Ac-DGGL(A)G-NH2) designed as a short, stable fragment derived from ciliary neurotrophic factor (CNTF). The original rationale: CNTF promotes neuron survival and synaptic plasticity in animal models, but it's a large protein that doesn't cross the blood-brain barrier well and triggers harsh side effects when given systemically. P21 was engineered to retain some of CNTF's neurotrophic effects in a smaller, intranasal-deliverable package.
How is P21 administered?
Intranasal, typically daily.
What is the half-life of P21?
~10 min — Short plasma half-life; intranasal delivery targets CNS directly.
Is P21 approved for human use?
P21 is investigational — not approved by the FDA, EMA, or MHRA for human use at the time of writing.
What does the evidence show for P21?
Evidence tier: Animal data primarily. Shadurskaya 2006 (Russian) dosed 50-500 μg/kg intranasal in rats for 7 days; Morris water maze latency improved ~25-30% vs control. No Western replication.
What is commonly monitored when researching P21?
Commonly tracked markers + signals: Subjective cognitive changes — memory, focus, learning speed, Sleep quality (some users report vivid dreams or disrupted sleep), Mood — irritability or anxiety if dosing too high, Nasal irritation or congestion from intranasal delivery, Neurological symptoms — headache, dizziness, any unusual sensory changes.
Open this in AIx Core for the full picture
Mechanism breakdown, receptor pathway diagram, full safety list, monitored items, source citations, and one-tap add-to-protocol. Free with any account.