The National Cancer Institute evaluated Gerson's claims and concluded that his data showed no benefit from his treatment.

[9] When the Nazis came to power in 1933 Gerson left Germany, emigrating to Vienna, where he worked in the West End Sanatorium.

[9] Gerson therapy is based on the belief that cancer is the result of a deteriorating metabolism from an impaired liver function.

[3] Gerson therapy aims to restore the body to health by repairing the liver and return metabolism to its normal state.

[3] Gerson therapy claims to treat the disease by having patients consume a plant-based diet including hourly glasses of vegetable juice, raw calf's liver extracts and various dietary supplements.

[3] In addition, patients receive enemas of coffee, castor oil and hydrogen peroxide or ozone.

[17] The original protocol also included raw calf's liver taken orally, but this practice was discontinued in the 1980s after ten patients were hospitalized (five of them comatose) from January 1979 to March 1981 in San Diego, California, area hospitals due to infection with the rare bacterium Campylobacter fetus.

This infection was seen only in those following Gerson-type therapy with raw liver (no other cases of patients having sepsis with this microbe, a pathogen in cattle, had been reported to Centers for Disease Control and Prevention in the previous two years).

[18] Gerson's therapy has not been independently tested or subjected to randomized controlled trials, and thus is illegal to market in the United States.

Similarly, case series by Gerson Institute staff published in the alternative medical literature suffered from methodological flaws, and no independent entity has been able to reproduce the claims.

A group of 13 patients sickened by elements of the Gerson therapy were evaluated in hospitals in San Diego in the early 1980s; all 13 were found to still have active cancer.

[21] A review of the Gerson therapy by Memorial Sloan-Kettering Cancer Center concluded: "If proponents of such therapies wish them to be evaluated scientifically and considered valid adjuvant treatments, they must provide extensive records (more than simple survival rates) and conduct controlled, prospective studies as evidence".

Serious illness and death have occurred as a direct result of some portions of the treatment, including severe electrolyte imbalances.

Coffee enemas "can cause colitis (inflammation of the bowel), fluid and electrolyte imbalances, and in some cases septicemia".