Damage to the brain:
Aspartame contains, inter alia, the free amino acid "aspartic acid", which can cross the blood-brain barrier. Referring now a "large" amount of aspartame on the brain can be supplied with too much calcium, which damage to the neural cells and thus damage to the brain can result. In extreme cases, this may have an increase of epilepsy or Alzheimer result.
https://healthsuperplace.wordpress.com/2015/06/06/muscle-forge-x/