Aspartame was first approved for use in 1981, but it wasn't until 15 years later that health concerns showed up. In 1996, a research paper showed that there had been a recent increase in brain tumors and hypothesized that this might be due to aspartame. Mind you, it didn't prove that was so. But the potential link was all the media needed to go crazy. TV shows, magazine articles, and newspapers all questioned whether the artificial sweetener was safe.
Further work using data from the National Cancer Institute showed that the increase in brain tumors really began in 1973, long before aspartame was introduced. Moreover, the increases in incidence of cancer were seen primarily in the elderly, which as a group, was not the major consumer of diet soda.
And there's more. A randomized, double-blind, placebo controlled trial
showed that aspartame didn't affect memory, behavior or mood. And a study published in 2006 followed more than 285,000 men and almost 190,000 women and
couldn't detect any relationship between aspartame and brain or blood cancer.