On his first overseas trip, Chesher worked in Britain as a research pharmacologist at Allen and Hanburys with Dr Harry Collier from 1953. Returning to Sydney in 1956, he worked in the medical documentation division at Nestle, then in 1959, he became chief information scientist with Smith Kline & French Laboratories under Dr David Ovedoff, who encouraged him to seek employment in academia and gave him time off to study for his MSc.
Following a sabbatical at the University of California, Los Angeles, as a visiting professor, Chesher resumed teaching at Sydney University and initiated his research into the effects of marijuana. Once his research was approved by the government, a National Health and Medical Research Council grant funded a study to determine the effects of marijuana on rats and mice.
Later when he was authorised to conduct research in humans, the university arranged a laboratory at Rozelle Hospital. To obtain subjects who were experienced users, he placed an ad in the student newspaper Honi Soit and was swamped by volunteers.
By the 1970s marijuana, although illegal, was being used, along with alcohol and tobacco, by a large portion of the community. Public opinion, then as now, was sharply divided on the relative harm to society of these drugs. There was continuing interest from the media and the law, particularly in relation to driving and traffic accidents.