P21
P21 (also written P021) is a synthetic CNTF-derived nonapeptide with an adamantane modification for blood-brain-barrier penetration, studied preclinically for hippocampal neurogenesis, BDNF upregulation, and memory; research protocols typically use 100-300 mcg (note: micrograms) subcutaneously daily in short cycles. Note the units carefully — P21 is dosed in micrograms, not milligrams.
Studied in rodent models for adult hippocampal neurogenesis, synaptic plasticity, BDNF-pathway activation, and cognition/memory endpoints, including Alzheimer's-disease-like impairment. Framed as a research-only neurotrophic compound with no human trials.
4 kDa it is far smaller than full-length CNTF (~23 kDa), which does not cross the BBB well. Research from Khalid Iqbal's group at the New York State Institute for Basic Research reports that P21 mimics CNTF trophic signaling, activating the MAP-kinase (Ras/ERK) and PI3K/Akt cascades and increasing brain-derived neurotrophic factor (BDNF). In rodent models this has been associated with increased adult hippocampal neurogenesis (shifting neural progenitor cells from quiescence toward proliferation and neuronal differentiation), enhanced dendritic and synaptic plasticity, reduced abnormal tau hyperphosphorylation, and improved learning and memory.
The evidence base is entirely preclinical — approximately five internally consistent rodent studies from a single laboratory — with no published human pharmacokinetics, no registered clinical trials, and no FDA approval. It is handled strictly as a research compound.
Research and community protocols reference roughly 100-300 mcg subcutaneously once daily (a common starting point is ~200 mcg in the morning). A 10 mg vial reconstituted with 2 mL of bacteriostatic water yields 5,000 mcg/mL, so 200 mcg is 0.04 mL (4 units on a U-100 syringe). No validated human dosing standard exists.
Onset in humans is not established. In rodent studies, neurotrophic and cognitive effects unfold over days to weeks of repeated dosing rather than acutely; community reports describe subtle effects around days 7-14, consistent with structural neurogenesis developing over weeks.
In nootropic research-community use it is often discussed alongside Semax (for immediate circuit/neuromodulatory effects layered onto slower structural neurogenesis), NAD+ (neuronal energy support), and pineal peptides such as Pinealon/Epitalon (neuroprotection). No stacking combination has been clinically validated. One anecdotal report describes severe emotional instability when combined with PE-22-28.
Log every dose, count every vial, and verify your batches — free in the goodtides app.
This page is educational reference material about compounds studied in research settings. It is not medical advice, and nothing here is a recommendation to buy, possess, or use any compound. Research findings described are from published literature; individual compounds may not be approved for human use. Talk to a licensed clinician about anything that affects your health.