Some case studies of individual people have reported headaches or migraine occurring after aspartame ingestion.[1][2][3] Furthermore, the Center for Disease Control (CDC) found that 67% (346/517) of people submitting a complaint about aspartame reported neurological/behavioral symptoms, including headaches, dizziness, and mood alterations after consuming aspartame-containing products.[4] Therefore, headaches are among the complaints about aspartame, but neither the data from the CDC nor observations from isolated case studies prove that aspartame causes headaches in all people.
To explore whether there is a causal link between aspartame and headaches, some randomized controlled trials have been completed. They show that the incidence of headaches after a single dose of aspartame does not differ from that after a placebo.[5] Meanwhile, daily administration of aspartame has increased headache frequency in some[6][7] but not all studies.[8] However, it is important to note that these studies include a small number of participants and the quality of their design and statistical approaches have been debated.[9][10][11]
Consequently, the low number of case studies and complaints suggests that aspartame-associated headaches are rare in the general population, and it is currently unclear whether aspartame consumption directly causes headaches or not. Further high-quality clinical trials would help remedy that lack of clarity. In the meantime, people who are susceptible to headaches following consumption of aspartame or aspartame-containing foods can choose to avoid such products.