The FDA has stated that based on its analysis of the data, that there is no basis to object to using refined stevia as a sweetener. The World Health Organization has also issued a report on the safety of the sweetener in normal doses.
Stevia is a sweetener made from a South American plant that is considered natural and has no calories. It is available for sale under many brand names, as of 2015. According to WebMD, while the refined Stevia that we see added to sodas, sweeteners and other foods is FDA approved and general considered healthy for human consumption, unrefined Stevia leaves and crude extracts have not been approved by the FDA, and these are not generally available in American stores or products, as of 2015.
The Center for Science in the Public Interest disputes the FDA’s claims that stevia is safe on the basis that the refined extract did not meet the FDA’s guideline for time spent testing, stating that food additives must be tested for 2 years on both rats and mice, and it was only tested on rats, and may have some damaging effects for which it was not adequately tested. This includes possible damage to chromosomes and DNA.