What are some of the toxic effects caused by consuming the artificial sweetener splenda?

Lots of things. Head aches, insomnia, funny taste in mouth, weight gain! (not a typo, they can make you gain weight!), loss of libido, memory loss, mood swings and on and on. Some people tolerate splenda and other artificial sweeteners without any obvious short term problems. Nobody really knows what will happen after using them for 50 years or more. Choose your poisons carefully!