Saccharin is one of six non-nutritive sweeteners and one of five artificial sweeteners approved by the FDA. The name is derived from the word Saccharine, meaning, “of, relating to, or resembling that of sugar.” It is the oldest known sugar substitute, dating back to its discovery in 1879 by Constantin Fahlberg.
It all started when Fahlberg, a Johns Hopkins University scientist working on coal-tar derivatives, spilled a chemical on his hand. Later, when eating dinner rolls he discovered an added sweetness and traced it back to the chemical.  The basic substance, benzoic sulfimide, is listed as being 200 to 700 times sweeter than sucrose depending on how its used, but has a bitter or metallic aftertaste. Often, this aftertaste is eliminated in prepared foods by adding other sweeteners. 
Harvey Washington Wiley, the head chemist of the Department of Agriculture’s Bureau of Chemistry, helped pass the Pure Food & Drug Act of 1906, with the purpose of protecting the public against adulteration of food.  Since saccharin does not affect blood glucose levels it became a sugar replacement for diabetics by 1907.  In 1908, “A top food safety official tried to ban saccharin from use as a sweetener, but the idea was adamantly opposed by President Theodore Roosevelt.”  The safety official was Wiley, he argued that a coal-tar derivative couldn’t be fit for human consumption.  In 1910, Roosevelt created the Referee Board of Consulting Scientific Experts to examine the effect of saccharin on human health and they determined it safe in small doses. However, food regulations called saccharin an adulterant in July of 1912 and prohibited its use in processed foods. Industry lawyers fought back and said the arguments against saccharin’s harm were weak. The ban was a result of a bureaucratic stalemate between regulators and industry. 
Saccharin could still be sold directly to consumers, and public perception of saccharin was still acceptable. During the sugar shortages of WWI and WWII, Monsanto, then the largest saccharin producer, marketed and sold saccharin as an inexpensive sugar alternative to price-conscious consumers. After the second war, saccharin production remained high from changing trends in America. More families were eating less home-cooked meals and more preprocessed and presweetened foods, which could contain saccharin. Government regulators and scientists were paying attention to the increased consumption of saccharin, as the debate over its health consequences was never settled. 
The Food Additives Amendment – to the Food, Drug, & Cosmetic Act of 1938 – was passed in 1958 due to the uncertainty of saccharin’s safety in the eyes of regulators and the public. The Amendment contained the “Delaney Clause“, after James J. Delaney, which required the FDA to prohibit the use of carcinogenic substances in food. In 1968, it would turn out that the only other artificial sweetener, cyclamate, was linked to bladder cancer in two studies and it was removed from the market a year later. In 1972, the FDA would remove saccharin from the list of food additives “generally recognized as safe” due to a clinical study showing a higher instance of bladder cancer in mice that consumed saccharin daily. 
In 1977, Canadian rat studies showed that saccharin itself was causing bladder cancer in rats. This led the FDA to to propose a saccharin ban , but congress passed the Saccharin Study & Labeling Act to prevent it from happening. Although there was no ban, products containing saccharin were required to have the following label, “Use of this product may be hazardous to your health. This product contains saccharin, which has been determined to cause cancer in laboratory animals.”  Saccharin was also added to the list of carcinogens.
However, studies since have shown that the results in the clinical study only applied to rats and not to humans.  According to the National Cancer Institute, “Human epidemiology studies (studies of patterns, causes, and control of diseases in groups of people) have shown no consistent evidence that saccharin is associated with bladder cancer incidence.” In 2000, saccharin was removed from the list of carcinogens and President Clinton would sign a bill — the Sweetest Act — to remove the warning label on saccharin products. 
It is said that saccharin is the most heavily researched artificial sweetener and carries no safety concerns – see here, here, here and here. Today, saccharin is known by brand names such as Sweet N’ Low, Sweet Twin, Sugar Twin, & Necta Sweet.