Every artificial sugar on the market is a very distinct chemical, with unique properties, so it's best to separately examine the three major sweeteners: sucralose (Splenda), aspartame (Equal), and saccharin(Sweet N' Low).

Sucralose/Splenda is the most recently developed artificial sweetener,and as such has been subjected to a more thorough review process than the other sweeteners. Sucralose is producing by taking normal sugar and turning some of the hydroxy (OH) groups into chloride groups.Sucralose, in over 100 human and animal studies, has been found tohave no major side effects. In humans, only about 7% of ingestedsucralose is actually digested, with the rest excreted unchanged from the body. Rat studies of intense (very intense) sucralose consumption have shown negative effects at 3g/kg feeding for a month-- Levels that in an average human would mean eating 17 thousand(!) Splenda packets a day, every day, for a month. Once in the environment,sucralose is broken down by bacteria, and does not accumulate in fatty tissues of animals (a concern for many environmental toxins).

Aspartame/Equal was an earlier developed artificial sweetener, and so had already been on the market when rigorous studies of it were conducted (and because of concerns, it has more health studies than almost any other substance discovered). Aspartame is made from the combination of two natural protein components of food, as partic acid and phenylalanine. Critics of aspartame has pointed out that similar rat studies as above (with huge doses) have caused health problems,and many consumers have attributed conditions such as migraines or fatigue to aspartame consumption. However, rigorous scientific studies have shown aspartame to be safe, with a headache in high doses and prolonged use being the only recognized side effect. The main reason that aspartame isn't used much these days is actually because it's hard to use in baking: it lacks both high-temperature stability and a long shelf life. Also, a small fraction of the population has the disease phenylketonuria, which makes aspartame dangerous for them because their bodies have trouble metabolizing the natural amino acid phenylalanine.

Saccharin/Sweet N' Low is a chemical made from coal tar (in fact, it was only discovered because the chemist who first made it spilled some sample on his hands before going home for dinner... when he licked his hands, he tasted intense sweetness, and viola!); and as such cannot be digested by the body. Like the other sweeteners, it has been intensely studied, and critics have at times accused it of causing cancer. But like the others, at sane doses, it has never been shown to pose any risk to human health.

These three artificial sweeteners have a long history of public health controversy, and like anything eaten should be consumed in moderation(17,000 packets of sugar a day is a bit too much...). However,there's little strong evidence for them having any large, negative effects on human health or on the environment. So, feel free to sweeten your day.