P21 is a nootropic peptide targeting improved neurogenesis. In animal studies, P21 has been shown to boost levels of BDNF (brain-derived neurotrophic factor), thus promoting neurogenesis (nerve growth) and inhibiting the formation of Amyloid plaques and Tau proteins seen in Alzheimer's disease. BDNF has been linked not just to enhanced neurogenesis, but to the down regulation of certain enzyme responsible for tau and amyloid plaque formation in Alzheimer's brains. P21 has been shown to improve cognition in animal models.