Stevia has a long history of use as a sweetening agent in foods and beverages. In the 1970s, Japanese manufacturers developed a stevia extract to serve as a substitute for sugar in various foods and drinks. In recent years, it has grown in popularity in the United States as well. Stevia appears generally safe when consumed as part of your diet, though consuming large amounts in supplemental form might pose some risks.
Pregnancy, Lactation and Fertility
The Memorial Sloan Kettering Cancer Center cautions against using stevia if you're pregnant. Check with your doctor before using stevia if you are breastfeeding as well. Beth Israel says stevia was purportedly used to prevent pregnancy, which raised concerns it might affect fertility. It adds, however, that "most, though not all," animal studies indicate it does not affect male or female reproductive health.
Effects on Blood Sugar and Blood Pressure
Drugs.com says animal and human studies suggest certain components of stevia might lower blood sugar levels and blood pressure. Not all studies found these benefits, however. While it is unlikely you would ever consume enough stevia to equal the amount of the active components necessary to produce these effects, you should keep this in mind if you take medications to treat these conditions. If you take it in supplemental form, however, it could prove problematic, as a concentrated extract will contain larger amounts of these active agents.
Consuming natural substances that lower blood sugar or blood pressure at the same time you take drugs used for these purposes could cause dangerous drops. You might require dosage adjustments in your medications to compensate for the effects of stevia. Only your doctor can safely determine dosage adjustments to your medications -- do not do this on your own.
Stevia does not have any significant adverse effects associated with it. Sloan-Kettering notes one stevia study in which four participants experienced muscle pain, abdominal fullness, nausea, abnormal weakness and lack of energy.
Other Safety Concerns
Because of its potential effects on blood pressure, stevia might also affect other aspects of the cardiovascular system. If you have any sort of heart condition, Beth Israel cautions against using high amounts of stevia extract without physician supervision. If you have liver or kidney disease, do not use large amounts of stevia without talking to your doctor first as these organs -- particularly when operating in a diseased state -- have a particular sensitivity to what you put in your body.