Additional Study Information: This is a 22-week treatment, multicenter, double-blind, placebo-controlled, parallel group, Phase 2 study to evaluate the efficacy, safety, and tolerability of the study drug E2027, in participants with Dementia with Lewy Bodies (DLB) Lewy Body Dementia - LBD. The main purpose of this research study is to find if a new drug called E2027 works in people who have DLB. People with DLB have impairment in their cognitive function (things like language, concentration, thinking, reasoning and memory). They may also have other symptoms affecting their movement and mental status. E2027 is an investigational study drug that is thought to cause an increase in levels of a brain chemical known as cyclic guanosine monophosphate (cGMP). cGMP is a substance involved in how cells communicate within the brain. Increasing cGMP levels in the brain may improve cognitive function. The purpose of this study is to assess the safety (symptoms and medical problems you may experience - known as side effects), and efficacy (how well the study drug treats DLB) of the study drug. If you decide to participate, you will take the study drug orally (by mouth) once a day.