May cause headaches

Many servings of diet Coke used each day may give some people headaches. This may be because of aspartame or another artificial sweetener that is included in diet soda.

When taken in large amounts, aspartame has been found to have a number of negative side effects. Some possible side effects are headaches, migraines, and irritability. Caffeine, which may be included in some diet sodas, has also been linked in some studies to headaches, but the evidence is conflicting. According to one research including 115 children, eliminating certain trigger foods from the diet, such as aspartame and caffeine, helped almost 87% of participants with their headaches.