Dr. Paul’s research efforts have established an important role for specific neurotransmitter receptors in mediating the central actions of various neuroactive drugs and particularly the delineation of the role of receptors for the inhibitory neurotransmitter GABA. His work has also helped shed light on genetic factors that dramatically increase risk for Alzheimer's and actually cause the brain abnormalities (plaques and tangles) that lead to the loss of neurons and the symptoms of the disease. While working at Eli Lilly and Company as Executive Vice President of Science and Technology and President of the Lilly Research Laboratories (LRL), his research team discovered a novel potential new treatment for Alzheimer's disease (an antibody called solanezumab) beleved to clear amyloid plaques from the brain. It is in the final phase of clinical testing.

Prior to assuming his position at Lilly, he served as Scientific Director of the National Institute of Mental Health (NIMH/NIH) in Bethesda, Maryland.