Cognitive & neuro
P21
A four-amino-acid fragment of ciliary neurotrophic factor studied in mice for neurogenesis, and nowhere near human trials.
What it is
P21 is a synthetic tetrapeptide (Asp-Gly-Gly-Leu) derived from ciliary neurotrophic factor, designed to mimic its neuroprotective effects without the full protein's inflammatory side effects. It is a laboratory research peptide: no form of it is an approved medicine, and no human trial of P21 itself has been published.
How it works
- 1
Mimics the active region of ciliary neurotrophic factor rather than the whole protein.
- 2
In mouse models it increased hippocampal neurogenesis and synaptic protein expression.
- 3
Reported reduction in tau phosphorylation in transgenic mouse models.
- 4
Its small size is claimed to allow passage across the blood-brain barrier.
- 5
No defined human receptor pharmacology has been established.
What it's studied for
Reported and studied effects
- Preclinical effects only; nothing established in humans
- Reported memory improvement in mice, not replicated in people
- No pharmacokinetic or safety data in humans
Research protocol notes
Research context onlyResearch context only - no approved human protocol exists. Published experiments used mice and cell cultures, typically microgram doses given intraperitoneally or directly into the brain, over days to weeks. Nothing about those doses translates into a human schedule.
These figures are described so you can understand what researchers did. They are not a dose, a schedule, or a suggestion — and they are not a substitute for a doctor.
Possible side effects and contraindications
Safety profile
Possible side effects
- Unknown in humans
- Potential for unverified identity or purity in research supply
- Inflammatory effects of the parent molecule are theoretical at fragment scale
Contraindications and cautions
- No established human use
- Pregnancy, childhood and any medical condition - no safety data
- Not a substitute for any approved treatment
A side-effect list is never complete, and these are not the only situations that warrant caution. Anything unexpected, or anything you are unsure about, should be discussed with a doctor before use.
Evidence assessment
Rodent and cell-culture data only, with no human pharmacokinetics, safety data or trials.
References
References link to published literature, regulator pages or literature indexes. Where a link points to a search, it collects the peer-reviewed work on that molecule rather than a single study.
Related
Related peptides
Other entries in Cognitive & neuro.
Cognitive & neuro
ACTH 4-10 (Org 2766)
The nerve-acting fragment of ACTH, developed as a drug candidate for nerve damage and cognitive decline, and abandoned.
Cognitive & neuro
BDNF (brain-derived neurotrophic factor)
The brain's main growth factor for plasticity: essential, widely measured, and not something a supplement can deliver.
Cognitive & neuro
Cerebrolysin
A porcine brain peptide mixture licensed in parts of Eastern Europe and Asia for stroke and dementia, without EMA or FDA approval.