Cyclamate (not legal in US)

Artificial sweetener: Banned in the United States. Allowed as a packaged (tabletop) sweetener in Canada and Europe, and also in diet soft drinks and foods in some other countries.
This controversial high-potency sweetener was used in the United States in diet foods until 1970, at which time it was banned because animal studies suggested that it caused cancer. (It is still permitted in Canada, Europe, and some other countries.) Now, based on animal studies, cyclamate (or a byproduct) is believed not to cause cancer directly, but to increase the potency of other carcinogens and to harm the testes.