Pharmacologist led study into effects of marijuana on the brain We’re sorry, this service is currently unavailable. Please try again later. Dismiss Pharmacologist led study into effects of marijuana on the brain By Terry Chesher Normal text size GREG CHESHER 1929–2020 Greg Chesher, who died on August 30, 2020, at the age of 91, was a scientist who undertook groundbreaking research into the effects of marijuana from the 1970s. He produced research quantifying the interactions of cannabis and alcohol on human performance that has informed a global field of research on cannabis and road safety. Greg Chesher, expert in the study of marijuana.