Aspartame: Sweetener used in Diet Coke possibly causes cancer, WHO set to declare

Aspartame is also linked in some studies to weight gain, GI disorders, mental health issues and more:

According to some studies, aspartame and other artificial sweeteners can lead to weight gain instead of weight loss 12. Aspartame has been linked to increased appetite, diabetes, metabolic derangement and obesity-related diseases 2.

One study showed that aspartame causes greater weight gain than a diet with the same calorie intake but no aspartame 1. Another study found that even acceptable daily intakes of aspartame might make you hungrier and lead to weight gain 3.

...some research suggests an association between aspartame intake and metabolic damage to the central nervous system (CNS), such as changes in enzyme and neurotransmitter activities 2. Aspartame acts as a chemical stressor by elevating plasma cortisol levels and causing the production of excess free radicals. High cortisol levels and excess free radicals may increase the brain’s vulnerability to oxidative stress which may have adverse effects on neurobehavioral health 3.

There is also some evidence that high-aspartame consumption may lead to weaker spatial orientation, irritability, depression, and other neurobehavioral conditions 14. However, these studies are limited in scope and further research is needed to determine the long-term effects of aspartame on human health.

Worth researching more, especially if you eat/drink anything with this stuff - and it's in a lot of food products.