It's the middle of the night. You've got chills and your stomach is turning. You're utterly exhausted, but restless, too -- and your symptoms keep getting worse. Now that you've come down with the flu, you'll need strong medicine to get through until morning. Mentally scanning the contents of your medicine cabinet, you arrive at the perfect solution. Given your set of symptoms, a little arsenic should do the trick.

Of course, ingesting straight arsenic would cause the very problems you're trying to eliminate -- or worse. But the super-diluted homeopathic remedy Arsenicum album accomplishes quite the opposite: According to homeopathy's proponents, it helps the body heal itself. The theory behind the 200-year-old system lies in this paradox: The same plant-, mineral-, and animal-derived materials that produce adverse reactions in large doses actually, in miniscule amounts (one part remedy to, say, 1 trillion parts water), stimulate the body to heal itself of these same disease-causing symptoms. This "Law of Similars" is commonly accepted in countries like France and Germany, where nearly one-third of all physicians prescribe homeopathic remedies.

If homeopathy has its detractors (and it does), it is due in part to the extremely diluted nature of the remedies. For instance, a remedy marked 200C (one part substance to 100 to the 200th power -- 10 followed by 400 zeros -- parts water) would contain very little, if any, of the original substance. For skeptics, this puts homeopathy squarely in the placebo realm. But proponents say the essence, or "memory," of that substance remains in the solution and has the power to heal. In fact, according to homeopathy, the more diluted a substance is, the more potent its effects.