MAPT and Alzheimer disease: Evidence from cell and animal studies suggest PDE-5 inhibitors have potential benefits for neuroprotection.4 One study has indicated that sildenafil is associated with a 69% reduction in Alzheimer’s disease risk and showed using induced pluripotent stem cells from patients with Alzheimer’s disease, sildenafil increased neurite growth and decreased phospho-tau expression.5 A recent clinical study has shown tadalafil does not increase cerebral blood flow in older people with symptomatic small vessel disease, the main cause of vascular cognitive impairment.6