He denounced unnecessary hysterectomies, radical mastectomies, and dangerous medications, reminding his readers of public health failures such as the 1976 swine flu outbreak and the damage caused to daughters of women who took the drug diethylstilbestrol during pregnancy.

[6] Mendelsohn had a full-time private pediatric practice from 1956 to 1967, and continued to see patients of all ages on a consultancy basis until his death in 1988.

Mendelsohn served as National Director of Project Head Start's Medical Consultation Service, a position he was later forced to resign after criticizing the “deadening atmosphere” of regular public schools.

“One of the unwritten rules in Modern Medicine is always to write a prescription for a new drug quickly, before all its side effects have come to the surface.” (Confessions of a Medical Heretic, p. 32) Mendelsohn opposed vaccinations for children, claiming the shots are dangerous and worthless.

[9] His book Confessions of a Medical Heretic was negatively reviewed in the Journal of the American Medical Association, the reviewer noted that "the technique of describing one specific situation or case history and then generalizing to all situations or all case histories is a dangerous one, and such extrapolations are carefully avoided by all responsible scientists.

"[11] Nutritionist Kurt Butler described Mendelsohn as a "Whiney-voiced crackpot who made himself rich and famous by leading the bash-doctors movements now in vogue.