Aspartame is an "insulin stimulant" and as such will not help you lose weight or control weight. This rebuttal to the official view provides an overview of what you should know.
Products that commonly contain aspartame: Soft drinks, over-the-counter drugs & prescription drugs (very common and listed under "inactive ingredients"), vitamin & herb supplements, yogurt, instant breakfasts, candy, breath mints, cereals, sugar-free chewing gum, cocoa mixes, coffee beverages, instant breakfasts, gelatin desserts, frozen desserts, juice beverages, laxatives, milk drinks, shake mixes, tabletop sweeteners, tea beverages, instant teas and coffees, topping mixes, wine coolers, etc.
Eliminate or replace prescription drugs that contain aspartame -- the pharmacist can tell you the ingredients of drugs.
For more, read Excitoxins: The Taste That Kills by Russell L. Blaylock, MD