In 1970s, in a study, Saccharin – an artificial sweetener, was administered to rats in excessive quantities . And it was found that Saccharin caused cancer in rats!
Here is that study – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1637197/
(i) This was not replicated in human beings. not everything dangerous to rat is dangerous for human beings and vice-versa
(ii) The rats were administered HUGE amount of saccharin. To get artificial sugar of that quantity, one has to drink 800 cans to match the amount given to rats
Saccharin was eventually banned in USA after the study and all artificial sweeteners were thus considered bad. However, saccharin was eventually reintroduced in US market following the debate
The FDA of USA, Europe, and many other countries have studied the artificial sweeteners and okayed their use in prescribed quantities. The carcinogenic effect of artificial sweeteners is not conclusively proven yet.
But that said, we will stay away from having Zero calorie drinks such as diet pepsi, diet coke etc too often.. but wouldn’t mind having one, once in a blue moon. In-fact the polluted air outside is perhaps more carcinogenic than having one diet coke in a month 🙂 (My opinion and anecdotal)
More literature, if you are interested in reading ..