Like many people these days, Lori Potter, a 50-year-old massage therapist living on Kauai, Hawaii, has explored alternative healing for everything from headaches to skin problems. So when she wanted to boost her immune system and lower her stress levels a few years ago, she made an appointment with a visiting practitioner of ayurveda, a medical system that originated in India thousands of years ago and has gained wide popularity in the United States. He prescribed herbal supplements, which he tested himself for impurities, to help boost her immunity. Soon, Ms. Potter said, she felt more energetic and her digestion was better. After two years, the practitioner stopped visiting the island, and she has not taken any supplements since, she said, because she has not met any practitioners she trusts. ‘You never know what’s really in these supplements,’ she said. ‘This is serious stuff, and you can’t just take them without knowing the source.’ Ms. Potter may be right to be wary. A report in the Aug. 27 issue of The Journal of the American Medical Association found that nearly 21 percent of 193 ayurvedic herbal supplements bought online, produced in both India and the United States, […]