Negative side effects of aspartame potentially include headaches, joint pain, anxiety attacks, memory loss, vertigo, seizures, weight loss, nausea, numbness, fatigue, depression and muscle spasms. Some other side effects that can arise include irritability, insomnia, vision problems, hearing loss, heart palpitations, loss of taste and tinnitus (ringing in the ears).
Some more drastic possible side effects include birth defects, diabetes, emotional disorders such as depression and personality changes, epilepsy, seizures, multiple sclerosis, chronic fatique syndrome, Parkinson's disease, Alzheimer's disease, heart palpitations, lymphoma, severe joint pain, excessive thirst, severe intolerance of noise, mental handicaps, blindness, hypoglycemia, brain lesions, brain cancer and tumors, and fibromyalgia.
Many of these more serious side effects are thought to be caused by long exposure to aspartame and high doses. Severe symptoms can also mimic these diseases and serious side effects while not causing the actual disease to occur in the human body.
There is a lot of controversy regarding aspartame as it was approved by the FDA in 1981. Before approving it, the FDA reviewed 37 studies that used animals and humans to determine the safety of aspartame. The FDA only warns those with phenylketonuria to limit their intake of the artificial sweetener because their bodies have a difficulty metabolizing phenylalanine, which is found in aspartame.