Saccharin, the most widely used artificial sweetener, has been listed as an "anticipated human carcinogen" in the USA since 1981. A review in 1997 by the National Toxicology Program did not remove it from this list. Cyclamate may be carcinogenic and may also cause chromosome breakage and atrophy of the testicles. Aspartame may cause brain damage or changes in brain chemistry and behaviour.
Rats that developed bladder cancers were fed the equivalent of thousands of cans of diet soda; studies of people who consume artificial sweeteners found no cancer risk. Bladder tumors develop only under urinary conditions specific to rats.