Saccharin and aspartame are two artificial sweeteners that have been rigorously studied for their safety in the past few decades. Although the U.S. Food and Drug Administration has deemed that both saccharin and aspartame are safe, various consumer safety groups and health professionals disagree with this assessment. Scientific studies have found links in animal studies between these sweeteners and cancer. Although the FDA reports that studies against both sweeteners are inconclusive, there is more evidence against aspartame, which could potentially mean that it's more dangerous.
Saccharin, a white crystalline powder, is about 300 times sweeter than sugar and contains no calories. It is one of the most commonly used artificial sweeteners in soft drinks and is used in a variety of other products, including fruit juices, chewing gum, mouthwash, toothpaste and pharmaceuticals. Saccharin was moved to the list of potential human carcinogens in 1980, according to the Environmental Protection Agency. However, a petition from the Calorie Control Council prompted the EPA to reassess the safety of saccharin. Based on evaluations that the National Toxicology Program conducted the EPA decided that saccharin was safe and removed it from the hazardous substances list. This led to a December 2000 repeal of the warning label that was previously required for saccharin products.
In the early 1970s, saccharin was thought to be a carcinogen when it was linked to bladder cancer. This link was based on studies done on rats. The National Cancer Institute notes that human trials have found no such link and that the mechanism that caused bladder cancer in rats does not exist in humans. Still, the Center for Science in the Public Interest believes that saccharin is unsafe and has issued the sweetener its lowest rating of "avoid." In a 1997 press release, the CSPI acknowledged that saccharin has not been proven to cause cancer in humans, but the CSPI contends that studies that have been done on saccharin indicate that it may still present a risk.
Aspartame, one of the most common artificial sweeteners, is a combination of two amino acids -- phenylalanine and aspartic acid. Aspartame is 200 times sweeter than sugar and, like saccharin, contains no calories. The National Cancer Society notes that rumors regarding potential negative health effects of aspartame, including cancer, have been circulating for many years. However, after reviewing a large number of studies on the safety of aspartame, both the FDA and the European Food Safety Authority agree that aspartame poses no risk to humans.
A 2013 major review of evidence on the safety of aspartame that the EFSA conducted, concluded that at aspartame's acceptable daily intake of 40 milligrams per kilogram of body weight, aspartame does not pose a safety concern. The CSPI disagrees with these findings and states that three large independent studies found a link between aspartame and cancer. The group believes these studies to be much more reliable than the smaller industry-funded studies that the EFSA used for evaluation. According to the CSPI, the largest of the three independent studies on aspartame found a link between aspartame and the development of rare kidney tumors in rats. The CSPI has also issued aspartame a rating of "avoid." Based on this information, aspartame may be worse than saccharin.