I got a phone call the other day from a man asking whether I did “alternative” medicine. When I told him that I wasn't in regular practice, he asked for a referral to someone who could provide this type of care. It made me think.

Complementary and alternative medicine (CAM) comprises a diverse group of treatments, ranging from symptomatic interventions to be used in conjunction with traditional therapies—therapeutic touch or meditation—to unique treatments meant to replace conventional chemotherapy or surgery. CAM includes complex and longstanding fields of study, such as acupuncture, ayurvedic medicine, and homoeopathy, but can also be as straightforward as taking a specific dietary supplement to lower blood pressure or blood lipid concentrations.

Americans love CAM. Over a third of them report having used some form of CAM therapy in the previous 12 months, and the use is increasing every year. Leading CAM therapies include natural products (supplements and herbals medicines and so on), meditation, chiropractic, and massage. Symptoms most commonly treated with CAM therapies …