Case reports of adverse events associated with coffee enemas raise concern about their use. Three deaths that seem related to coffee enemas have been reported in the literature. Salmonella enteridis group D and Campylobacter fetus intestinalis were cultured from stool and blood of one patient who died shortly after treatment at the Gerson Institute clinic. This death could not be directly linked to the practice of coffee enemas because more tests could not be performed.
Case reports of two more deaths following treatment at the Gerson Institute were both attributed to electrolyte imbalance after autopsies were performed showing no active inflammation of the colon. 
A third case report of electrolyte imbalance that did not result in death describes a patient who developed hyperkalemia while undergoing Gerson therapy. No other reports of adverse effects have been identified.References
- Margolin KA, Green MR: Polymicrobial enteric septicemia from coffee enemas. West J Med 140 (3): 460, 1984. [PUBMED Abstract]
- Eisele JW, Reay DT: Deaths related to coffee enemas. JAMA 244 (14): 1608-9, 1980. [PUBMED Abstract]
- Nagasaki A, Takamine W, Takasu N: Severe hyperkalemia associated with "alternative" nutritional cancer therapy. Clin Nutr 24 (5): 864-5, 2005. [PUBMED Abstract]