However, the health harms of artificial sweeteners have been, historically, overstated. Studies on aspartame have shown that, although some individuals are sensitive to aspartame, and the sweetener is broken down into potentially toxic substances, there is not enough of those substances to cause any issues in most people. It seems to cause seizures in animals, but human studies have not backed this up.
The use of artificial sweeteners was linked to increased risk of cardiovascular disease, though it is unclear if it is the diet or lifestyle of the people or the artificial sweetener itself that is to blame.
According to the FDA, there is no clear evidence of artificial sweeteners causing cancer in humans, despite studies in rats showing a higher risk of bladder cancer. Rat urine, especially in male rats, is different than human urine, and this difference is what allows the artificial sweetener, in this case, saccharine to damage the bladder walls. This only occurs in rats, not humans.
Stevia is a little more complicated.
Studies imply that it is safe, but in rats it reduced fertility and raised the possibility of other issues in the rats. In the lab it can be turned into a cancer promoting mutagen, though it is unclear whether it does so in the body. Many nations consider it unacceptable for use in food, and the FDA classes it as a “dietary supplement.” Whether this is justified is unclear.
Other sweeteners have no major health controversies attached to them. Complicating matters, some studies have also shown benefits:
A 2018 study concluded that stevia, the extract of Stevia rebaudiana Bertoni, isn’t linked to serious health problems. It did cause weight loss, but this was possibly due to the lower sugar intake effecting the gut microbiome, which is an effect that can be seen in studies with other sweeteners as well. The gut microbiome is powerfully linked to weight and inflammation, so this is something to note.
This article by Healthline seems to refute the anti health claims and concludes that artificial sweeteners are beneficial if used to reduce the amount of sugar in the diet. It is a complicated issue and there is compelling evidence both ways. Adding to this complexity is the fact that studying one sweetener does not tell you much about all of the others because they are chemically distinct.