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 This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.