Aspertame

MAY cause-
abdominal pain, anxiety attacks, arthritis, asthma, asthmatic reactions, bloating/edema, blood sugar control problems (hypoglycemia or hyperglycemia), brain cancer (Pre-approval studies in animals), breathing difficulties, burning eyes or throat, burning urination, can't think straight, chest pains, chronic cough, chronic fatigue, confusion, death, depression, diarrhea, dizziness, excessive thirst or hunger, fatigue, feel 'unreal', flushing of face, hair loss (baldness) or thinning of hair, headaches/migraines, hearing loss, heart palpitations, hives (Urticaria), hypertension (high blood pressure), impotency and sexual problems, inability to concentrate, infection susceptibility, insomnia, irritability, itching, joint pains, laryngitis, "like thinking in a fog," marked personality changes, memory loss, menstrual problems or changes, muscle spasms, nausea or vomiting, numbness or tingling of extremities, other allergic-like reactions, panic attacks, phobias, poor memory, rapid heartbeat, rashes, seizures and convulsions, slurring of speech, swallowing pain, tachycardia, tremors, tinnitus, vertigo, vision loss, and weight gain.

some research in female rats approved it - some of them got kidney cancer, others got it on the periphal nerves (mainly in the brain)

now, go check your diet soda/pepsi/cola/whatever
it contains it :x

http://en.wikipedia.org/wiki/Aspartame#Health_effects_controversy