Stevia is a small shrublike herb from which you can extract a zero-calorie sweetener that's about 200 times sweeter than sugar. The Food and Drug Administration, or FDA, has approved the use of stevia as Generally Recognized as Safe, or GRAS, and it is now available in little packets you can use in your morning coffee instead of sugar. Stevia tastes different from table sugar, and it does not behave the same way, so it can't be used as a direct sugar substitute in many recipes. Questions remain about stevia's effects on blood pressure, blood sugar and reproductive health.
The stevia plant is native to Paraguay, where it has long been used for both its medicinal and sweetening properties. According to the University of Nebraska-Lincoln Extension office, Paraguayans use the to treat high blood pressure and obesity. The FDA has not approved stevia for this use, but a 2003 study in "Clinical Therapeutics" did indicate some long-term improvement in high blood pressure among participants taking a stevia supplement. Stevia may also help balance blood sugar.
Although the Japanese began using stevia as a food sweetener in the 1970s, the United States initially banned its use. The FDA cited concerns about safety in large doses. The administration was particularly concerned about the possibility that the sweetener might increase the risk of cancer or cause reproductive issues. Even though stevia is not officially approved to treat diabetes and high blood pressure, if you are taking medications for those conditions, be careful not to use large amounts of stevia to prevent adverse reactions.
Stevia is sweet, but it isn't sugar and it doesn't behave the same way. It has a different flavor, which you might find bitter. You may not taste the sweetness as fast as you do with regular sugar, but once you do, it might stay on your tongue longer than you expect. Stevia doesn't react with yeast like sugar does, so it won't make bread rise the same way. You will need to find special recipes that use stevia, since you can't just substitute it for sugar and expect the same results.
The Japanese have used stevia for more than 40 years, and there is still minimal incidence of problems. If you are trying to cut back on your calorie intake to lose weight, but you don't like the risk involved with saccharin, or if you have problems tolerating aspartame, then stevia might be a good alternative for you. The sweetener isn't for everyone -- you may experience headaches or an upset stomach. If you want to try it out, use it in small doses to see if you can tolerate it. If you are concerned about the health issues, ask your physician for advice.