P21

P21 is a synthetic peptide derived from the active region of ciliary neurotrophic factor (CNTF) that has been shown to promote neurogenesis in the hippocampus. Unlike full-length CNTF which has poor brain penetration and significant peripheral side effects, P21 is small enough to cross the blood-brain barrier while retaining neurotrophic activity. Research demonstrates P21 enhances adult hippocampal neurogenesis, increases synaptic plasticity, and improves cognitive function in animal models. Studies show the peptide rescues cognitive deficits in models of Alzheimer's disease by promoting new neuron formation and improving spatial memory. The mechanism involves activation of CNTF receptor signaling pathways that support neuronal survival and differentiation. P21 has shown promise for neurodegenerative conditions, age-related cognitive decline, and potentially depression given the link between hippocampal neurogenesis and mood. The peptide represents a novel approach to supporting brain health through targeted neurotrophin-mimetic activity. Research continues into optimal dosing, duration of treatment, and clinical applications for cognitive disorders.

Evidence is limited to a single peer-reviewed Alzheimer's mouse study and related CNTF-pathway research. There are no human data, no pharmacokinetic characterization in humans, and no clinical trials. The compound is sold only for laboratory research.

P21/P021 is a small peptide derived from the active region of ciliary neurotrophic factor (CNTF), designed to retain neurotrophic activity while crossing the blood-brain barrier (full-length CNTF does not). In the Alzheimer's mouse study it was given chronically by the oral route. No human half-life or pharmacokinetic data exist.