Jacob is a historian of science and medicine, and of the United States. His work focuses on the history of drugs such as nitrous oxide, cannabis, and peyote in late 19th and early 20th century America.

His dissertation investigates topics such as how the study of these drugs intersected with the development of quantitative and qualitative methods in the early history of experimental psychology. He also looks at how philosophers used drug experiences to either support or attack Hegelianism and various other forms of Idealist philosophy which were popular during this period. Finally he investigates how contemporary cultural context shaped the sometimes mystically illuminating, and other times terrifying, unintentional hallucinogenic experiences that many individuals had while undergoing anesthesia at the surgeon or dentist.

Overall his goal is to show that many aspects of the history of mind-altering drugs which are generally thought to begin in the 1950s or 1960s, such as their scientific study and associations with mystical experiences in American popular culture, have a much longer history that stretches back into the 1800s.