Nicholas James Gonzalez (December 28, 1947 – July 21, 2015) was a New York–based physician known for developing the Gonzalez regimen (or Gonzalez protocol), an alternative cancer treatment. Gonzalez's treatments were based on his belief that pancreatic enzymes were the body's main defense against cancer and could be used as a cancer treatment. His methods have been generally rejected by the medical community, and he has been characterized as a quack and fraud by other doctors and health fraud watchdog groups. In 1994 Gonzalez was reprimanded and placed on two years' probation by the New York State Medical Board for "departing from accepted practice".

In one non-randomized clinical trial of terminally ill people with pancreatic cancer, the Gonzalez-treated patients were found to have died much earlier than those treated with conventional chemotherapy. A better quality of life was also reported by the chemotherapy arm.

Gonzalez was born December 28, 1947, in Flushing, New York. He graduated Phi Beta Kappa and magna cum laude from Brown University, with a degree in English literature. From 1970 to 1977, Gonzalez worked as a journalist for Time Inc. and as a freelance writer, covering a variety of health-related topics, including a July 1972 cover story in New York Magazine, a 1976 cover story for Family Health Magazine, and an article for Prevention Magazine. Gonzalez became interested in medical research, and in cancer research in particular while covering these topics.

Gonzalez completed postgraduate premedical work at Columbia University and received his medical degree from Cornell University in 1983. Gonzalez worked with Robert A. Good at Memorial Sloan-Kettering Cancer Center while in medical school. After receiving his medical degree, Gonzalez completed an internship in internal medicine at Vanderbilt University. From 1984 to 1986, Gonzalez worked with Good again, completing a fellowship in immunology while at University of Oklahoma and All Children's Hospital in St. Petersburg, Florida.

Gonzalez died of a suspected heart attack on July 21, 2015, at age 67. A conspiracy theory subsequently spread that Gonzalez was murdered as part of a systematic plot to kill "holistic" practitioners.

Gonzalez's treatment methods, which he started using in 1987, were developed from previous work by the orthodontist William Donald Kelley. Gonzalez believed that cancer was caused by a poor diet, a problem compounded when one does not eat a diet that corresponds with one's "metabolic type"; and that environmental pollution and daily stress contributed to health problems. The Gonzalez regimen proposed as a treatment a cure-oriented change in lifestyle and nutrition, the use of oral pancreatic enzymes, large numbers of dietary supplements (up to 150 pills per day) and twice daily coffee enemas. A clinical trial on Gonzalez's treatments produced "limited and inconclusive" results regarding the efficacy of the Gonzalez Regimen as a treatment for cancer.

In 1999 Gonzalez published an article describing prolonged life in a small, select group of patients with pancreatic cancer in the peer-reviewed journal Nutrition and Cancer. Subsequently, others concluded that the longer survival time reported by Gonzalez was due to selection bias and other confounds.

Like his mentor, William Donald Kelley, Gonzalez's treatment method was rejected by the mainstream medical establishment. Gonzalez was characterized as a quack and fraud by other doctors and health fraud watchdog groups, and in 1994 he was reprimanded and placed on two years' probation by the New York state medical board for "departing from accepted practice". Gonzalez was given two years of probation with a stipulation that he undergo retraining and psychological examinations, and do 200 hours of community service. He was fully licensed to practice in New York.