According to Fizzies.com (Oct 26, 2012): In 1968, the FDA came out and banned the the artificial sweeteners used to make Fizzies, called cyclamates. Cyclamates were an essential part of making Fizzies tablets, and the scientist didn't know how to reformulate. Retailers were allowed to sell out their remaining stock through 1970, but after that Fizzies disappeared. In 1995, some of the original makers of Fizzies contacted effervescent contract manufatures Amerilab Technologies in Plymouth Minnesota, hoping the scientist there could reformulate Fizzies using aspartame. Fizzies were back on the market, but their re-emergence was short-lived, and Fizzies filed for bankruptcy in 1996.
Fizzies are now available again from Amerilab Technologies.