Even after ten years of federally funded research, very little is known about whether most alternative therapies work at all and which methods are safe. In these excerpts from their FRONTLINE interviews, researchers, practioners and skeptics discuss the scant evidence we have and why it's so hard to come by.

Critics of alternative medicine often dismiss reports of successful treatments by attributing the success to the "placebo effect": if the patient feels better, it's because he believes the therapy will work, not because of any actual physiological effect. Does it really matter? Medical historian James Whorton, alternative practioner Andrew Weil, and Harvard University's Marcia Angell and Tom Delbanco discuss the controversy.

Researching the medical literature for studies on alternative therapies can be a frustrating experience for doctors and patients alike. Although there are thousands of studies and reports, not all published studies are equally authoritative. Here's a brief overview of the different types of reports you may come across, and an explanation of why solid evidence on alternative medicine is so hard to come by.