P21
Also known as: P021, CNTF-derived peptide
Grey-Market Compound. This compound is not approved by the FDA or any major regulatory authority. No established regimen exists. Products available outside of regulated channels lack standardized manufacturing, quality control, and potency verification. Consult a qualified clinician. Research-only risks apply.
Overview
Clinical Summary
P21 is a small synthetic peptide derived from the active region of ciliary neurotrophic factor (CNTF). It was designed to replicate the neurotrophic and neurogenic effects of CNTF while being small enough to cross the blood-brain barrier and resist enzymatic degradation. In transgenic Alzheimer disease mouse models, P21 promoted hippocampal neurogenesis, reduced tau pathology, and improved spatial memory. No human clinical trials have been conducted.
Plain Language Summary
P21 is a research peptide designed to mimic a natural brain growth factor called CNTF. In mouse studies, it promoted the growth of new brain cells and improved memory in Alzheimer disease models. It has never been tested in humans and is only available through grey-market sources. Its safety in people is unknown.
Mechanism of Action
P21 is a modified tetrapeptide derived from the biologically active region of CNTF (residues 148 to 151) with an adamantylated glycine group added to enhance blood-brain barrier penetration. Unlike full-length CNTF, P21 does not activate the CNTF receptor/JAK-STAT pathway and therefore avoids the appetite-suppressing and weight-loss side effects of CNTF. Instead, P21 is proposed to act by competitively inhibiting leukemia inhibitory factor (LIF) signaling, which normally suppresses neural stem cell proliferation. By relieving this LIF-mediated inhibition, P21 promotes neurogenesis in the dentate gyrus of the hippocampus and enhances dendritic complexity.
Evidence Summary
Bolognin et al. (2012) demonstrated that P21 reduced tau hyperphosphorylation, increased hippocampal neurogenesis, and improved spatial memory in 3xTg-AD mice (a triple-transgenic Alzheimer model). Blanchard et al. (2010) showed that P21 enhanced dentate gyrus neurogenesis and memory in wild-type mice. Both studies originate from the same research group. No independent replication has been published. No human pharmacokinetic, pharmacodynamic, dosing, or safety studies exist.
Safety Profile
No human safety data exist for P21. No formal toxicology studies have been published. The compound was designed to avoid CNTF receptor activation and its associated systemic effects, but this has only been verified in rodent models. Long-term effects on neurogenesis, including any risk of promoting brain tumor formation, have not been assessed.
Contraindications
- No established contraindications due to absence of human data
- Theoretical concern with CNS tumors (promotes neural cell proliferation)
- Pregnancy and breastfeeding (no safety data)
Adverse Events
- No human adverse event data available
- Theoretical risk of aberrant neurogenesis
- Unknown systemic effects
Interactions
- No drug interaction data available
- Theoretical interaction with LIF signaling modulators
- Unknown interactions with neuropsychiatric medications
Regulatory Notes
P21 has no regulatory approval in any jurisdiction. It has not entered clinical trials. It is available through grey-market peptide vendors without quality controls. The original research was conducted at the New York State Institute for Basic Research in Developmental Disabilities.
Monitoring Considerations
No established monitoring guidelines. In a research context, cognitive testing and neuroimaging could be considered. No validated biomarkers exist for assessing P21 response in humans.
These are general considerations for clinical awareness and do not constitute prescriptive monitoring recommendations for any individual patient.
Stability and Handling Notes
No pharmaceutical-grade stability data available. Grey-market preparations are supplied as lyophilized powder. Vendor recommendations (not validated) suggest storage at minus 20 degrees C for long-term and 2 to 8 degrees C after reconstitution. No pharmacopeial standards exist.
References
- 1preclinical
Peptide P21 Prevents Neurodegeneration and Promotes Neurogenesis in an Alzheimer Disease Mouse Model
Bolognin S, Blanchard J, Wang X, et al. (2012). Molecular Neurobiology
Key findings: P21 treatment reduced tau hyperphosphorylation, increased neurogenesis in the hippocampus, and improved spatial memory in 3xTg-AD mice.
Limitations: Single transgenic mouse model. No human pharmacokinetics or dosing data. Not replicated by independent groups.
View source - 2preclinical
Small Peptide Derived from CNTF Enhances Dentate Gyrus Neurogenesis and Cognitive Function
Blanchard J, Wanka L, Bhatt DK, et al. (2010). FASEB Journal
Key findings: P21 increased dentate gyrus neurogenesis and improved memory performance in wild-type mice. Proposed mechanism involves inhibition of leukemia inhibitory factor (LIF) signaling.
Limitations: Rodent data only. Mechanism of action not fully elucidated. No safety or toxicology assessment.
Last reviewed: 2026-03-24 | Version: 1 | Status: Published
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