Gerson's therapy has not been independently tested or subjected to randomized controlled trials, and thus is illegal to market in the United States.
Gerson therapy can lead to several significant health problems. Serious illness and death have occurred as a direct result of some portions of the treatment, including severe electrolyte imbalances. Continued use of enemas may weaken the colon's normal function, causing or worsening constipation and colitis. Other complications have included dehydration, serious infections and severe bleeding. Moreover, the American Cancer Society considers this "therapy" to be completely ineffective against cancer.
To date, no one can answer why consumption of coffee is more effective through selective self sodomy than it is via more tradition and conventional oral methods.