Cyclamate as a food additive is a non-nutritive sweetener that is used in over 100 countries, not including the United States. The name cyclamate is derived from cyclamic acid, with its sodium or calcium salts being used as the sweetener. It is the second oldest – with saccharin being the oldest – known sugar substitute, dating back to its discovery in 1937 by Michael Sveda.
The discovery occurred when Sveda, as a graduate student at the University of Illinois, picked up his cigarette off a lab bench while working on the synthesis of anti-pyretic (anti-fever) drugs in the laboratory. When he put the cigarette back in his mouth he discovered the sweet taste of cyclamate.  Cyclamate is listed as being approximately 30 – sometimes up to 50 – times sweeter than sugar. 
Sveda received the patent for cyclamate in 1939 while he was an employee of the DuPont Company.  DuPont would later sell the patent to Abbott Laboratories, and they would go on to submit a New Drug Application for cyclamate in 1950.  The FDA would approve sodium cyclamate in 1951. In 1958 it was put on the GRAS list and marketed to diabetics – to control insulin levels – and as a alternative sweetener. 
One of the benefits of cyclamate is a synergistic effect when it is combined with other low-calorie sweeteners, such as saccharin. The combination of the two sweeteners tastes sweeter and any aftertaste when using only one sweetener can be masked. A widely used combination during the 1960’s included 10 parts cyclamate to 1 part saccharin – a 10:1 ratio. 
Trouble first struck cyclamate in 1966 when, ” a study reported that intestinal bacteria could desulfonate cyclamate and produce cyclohexylamine, a compound that was suspected to have toxicity in animals.”  More trouble would come after the publication of a 1967-69 multigenerational study that started with 70 rats being fed a 10:1 mixture of cyclamate and saccharin over the 2 year period. The dosages, ranging in equivalence to 30-150 soft-drink servings a day, ended with 12 of the 70 rats developing bladder cancer.  This led the FDA to announce the U.S. ban of cyclamate that would take effect on September 11, 1970.  A December 7, 1971 patent declaring a cyclamate-free artificial sweetener was issued.
Since the ban over 75 studies have said to prove cyclamate safe for human consumption. In 1984, “the Cancer Assessment Committee of the U.S. Food and Drug Administration (FDA) came to the conclusion that cyclamate is not carcinogenic.” In 1985, “this finding was confirmed in an independent evaluation of the report by the U.S. National Academy of Sciences.” Currently, “the World Health Organization, the Joint FAO/WHO Expert Committee on Food Additives (JECFA), the Scientific Committee on Food (SCF) of the European Commission (now the European Food Safety Authority (EFSA), and food safety authorities in Mexico have approved its use in a wide range of foodstuffs. A petition for the re-approval of cyclamate is currently under review by the U.S. FDA.”  The FDA is said to be waiting for studies that can prove whether, “cyclamate is a tumor promoter in animals, or a co-carcinogen — that is, a substance that may increase the likelihood of cancer from another substance.” 
Today, cyclamate can be found in the following products in countries that permit its use. Sweetener brands include Assugrin (Switzerland, Brazil), Suitli (Bulgaria), Sucaryl, Sugar Twin (Canada), Cologran (Germany), Novasweet (Russia), and it has been added to Coca-Cola Zero (in Austria, Greece, Germany, Poland, Latvia, Lithuania, Estonia,
Venezuela, and Mexico).
Here is a fact sheet on cyclamate.