Whether or not stevia itself is dangerous is disputed, as reported by Livescience. Although the U.S. Food and Drug Administration hasn't approved stevia leaves to be used as food additives, it has given some companies the approval to use rebaudioside A, which is a chemical found in stevia.
There are concerns about the effects of stevia on blood sugar levels, as well as reproductive, cardiovascular and renal systems, the FDA reports. On the other hand, the FDA does not object to the use of certain refined stevia preparations in food. These preparations are lawfully added to food products in the United States.