The main purpose of this study is to look at how safe the study drug (mevidalen) is and whether it works to alleviate symptoms when given to people with mild to moderate Alzheimer Disease (AD) dementia. This is done by looking at participants: thinking and memory (cognition), everyday activities and sleep, AD symptoms, physical activity, irritability or anxiety. The study is expected to last approximately 26 weeks and may include up to 14 visits.