Saccharin is derived from Coal Tar. It contains sulfonamides, making it the equivalent of a sulfa drug. Anyone who is allergic to Sulfa Drugs also cannot have this product.
Saccharin has been found to cause Cancer in animals.
More information can be found here:
http://www.medicinenet.com/artificial_sweeteners/page6.htm
http://naturalhealthsherpa.com/saccharin-danger-side-effects/52849