THE MOOD MOLECULE

For Chicago journalist Susan Schwendener, the symptoms were as familiar as the runny nose of a cold or the scratchiness of a strep throat. "You can't sleep, you can't eat, you lose weight because your mood's so blue." Schwendener, 33, suffered her first bout of depression as a teenager. She started taking Prozac 10 years ago. "The pain," she says, "sort of evaporated over time." By the age of 21, Beth Herwig, now an executive assistant in St. Louis, Mo., tipped the scales at more than 500 lbs. At 29, after years of yo-yo dieting, she was carrying 545 lbs. on...