Stevia is a natural sweetener obtained from a shrub that is grown in Brazil, Paraguay, southeast Asia, and elsewhere. Crude stevia extracts are about 100 times sweeter than sugar, while the actual sweet chemicals are about 200 times sweeter. One of those chemicals, rebaudioside A, or rebiana, is sold in packets and used in diet beverages and other foods. It is marketed under such brand names as Truvia and PureVia. 

Stevia and its derivatives are said to be the holy grail of high-potency sweeteners, because they are obtained from a natural source, unlike the controversial synthetic sweeteners (saccharin, aspartame, acesulfame-K, sucralose). However, some people perceive stevia and its sweet derivatives to have a foul taste in certain foods.  Moreover, it should be better tested.

Resources

• FDA Issues Midnight Go-ahead for Potentially Harmful Stevia Sweetner—Statement of Executive Director Michael F. Jacobson: December 18, 2008
• Stevia: What's the Rush?—Statement of CSPI Executive Director Michael F. Jacobson: December 15, 2008
• Lab Tests Point to Problems with Trendy New Sweetener—Press Release: August 28, 2008
• Stevia: Sweet...but How Safe?—Nutrition Action Healthletter: October 2008
• CSPI's Letter to the Food and Drug Administration
• UCLA Toxicologists' Report on Stevia