More additives in diet drinks that can cause problems. Acesulfame-K or Ace-K is an artificial sweetener used in Coke Zero. There have been inadequate studies to conclusively prove this substance is totally safe for human consumption. This additive was approved even though it failed to meet FDA standards.The problems surrounding acesulfame K are based on the improper testing and lack of long-term studies. Acesulfame K contains the carcinogen methylene chloride. Long-term exposure to methylene chloride can cause headaches, depression, nausea, mental confusion, liver effects, kidney effects, visual disturbances, and cancer in humans. There has been a great deal of opposition to the use of acesulfame K without further testing, but at this time, the FDA has not required that these tests be done.