Davies' research was focused on the biochemistry of Alzheimer's disease. His early work was in the development of the currently approved drugs for Alzheimer's disease: Aricept, Exelon and Razodyne. He was interested in the pathway of Alzheimer's disease, and said that the disease may be a process of uncontrolled cell cycle division. He had evidence that the switch that drives the cell cycle of neurons, which is a one-time event when the neuron is born, is somehow tripped and reactivated late in life. He and his team designed an experiment to turn on the cell cycle in laboratory models. They put a viral oncogene into differentiated neurons and watched as pathological events progressed. In 2004 Davies and his collaborators identified a marker in cerebrospinal fluid (CSF) that can distinguish Alzheimer's disease from normal ageing, as well as discriminate between Alzheimer's and other forms of dementia. The overall goal of Davies' research was to develop treatments to slow or halt the progression of Alzheimer's disease.