His similarly harassed colleague Louis Jolyon West remarked: "I was lucky that I was a full-time professor in a big university like UCLA. Others, like Harvard's Jack Clark. who was primarily in private practice, nearly had their lives ruined by the Scientologists."
The Psychiatric Times, when naming him 1991 psychiatrist of the year, described him as "a quiet, courageous man of conviction, who was fighting an all-too-lonely and unappreciated battle against well-financed, ruthless organizations."
- Testimony of John Clark regarding cults Read on 3 November 1977 by Leo J. Ryan to the United States House of Representatives
- Clark, John G. Cults. Journal of the American Medical Association. 242, 279-281. 1979
- Clark, J.G., et al.: Destructive cult conversion. Weston, MA: American Family Foundation. 1981
- Clark, John G.: On the further study of destructive cultism. In Halperin (ed.), 363-368 1983
- Langone, Michael D. and John G. Clark, Jr.: New religions and public policy: research implications for social and behavioural scientists Weston (MA.): American Family Foundation 1983
- Leo J. Ryan Award, 1985
- Psychiatrist of the year, The Psychiatric Times, 1991
- Dr. John Clark, 73, Psychiatrist was authority on danger of cults, Tom Long, Globe Staff, 10/09/99, The Boston Globe
- John Clark, 73, Psychiatrist Who Studied Sects, New York Times, October 18, 1999, Eric Nagourney
The Church of Scientology objected strongly to Clark's assertions, and the church and Clark battled in court. Clark said the church had engaged in a campaign of harassment against him. In 1988, he settled with the church and received an undisclosed amount of money, but agreed never to discuss the group publicly again.
- "Prozac Frees Ex-Scientology Leader from Depression" Psychiatric Times, June 1991
- Prozac frees Ex-Scientology Leader from Depression, The Psychiatric Times, Volume VIII, June 1991