Stevia leaf extract is a food additive that is Generally Recognized As Safe (GRAS) by the US FDA. Crude stevia, or whole-leaf stevia, does not have GRAS status from the US FDA.
One way the FDA accomplishes its food safety mission is to distinguish between “food additives” and “dietary supplements.” Food additives (such as stevia leaf extract) can be approved by the FDA or declared to be GRAS. Food additives are described as any substance intentionally added to a food. Because stevia leaf extract has GRAS status, it is able to be sold commercially in stevia-based sweeteners available for purchase at retail in the US.
Dietary supplements are products taken by mouth that contain a dietary ingredient. Crude stevia or whole-leaf stevia—different from the highly purified forms of stevia leaf extract—are currently not permitted for use as sweeteners as per the FDA and do not have GRAS status. Crude stevia is considered to be a dietary supplement, which enables it to still be sold online or at natural specialty stories.
Read the full FDA opinion here.