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 her 5-ft. 4-in. frame. Then Herwig went on a combination of fenfluramine and phentermine, popularly known as fen/phen. "It's not that I don't want that Twinkie still," says Herwig. "But before, I would see it, and there was almost nothing that could stop me." Today she weighs just 265 lbs.

Brian Goodman, 20, is obsessed with the idea that disaster and death are about to strike his family. The only way to stave off catastrophe, his mind tells him, is to follow self-imposed rituals to the absolute letter: making coffee in a way that never varies, driving around Los Angeles along the same route every day. A classic victim of obsessive-compulsive disorder, Goodman has been in treatment since he was seven, without much change. Now he is on Zoloft. "Before the medicine," he says, "it was like living in hell."

At first glance, these stories seem completely unrelated--three profoundly different disorders treated with three different drugs. Yet all three medications have one crucial element in common: they target the brain chemical serotonin. Though serotonin has been known to researchers for nearly a half-century, only in recent years have neuroscientists begun to understand how important this one substance is to the functioning of the human psyche. Serotonin, or the lack of it, has been implicated not only in depression, uncontrollable appetite and obsessive-compulsive disorder but also in autism, bulimia, social phobias, premenstrual syndrome, anxiety and panic, migraines, schizophrenia and even extreme violence.

The growing awareness of serotonin's central role in mood and emotion has been paralleled--and in some cases driven--by a boom in drugs that target serotonin more or less specifically. Among them are such popular antidepressants as Elavil, Prozac, Zoloft and the hot new herbal medication St. John's wort; powerful appetite suppressants including Redux and fenfluramine; and antipsychotics such as clozapine. Like every other drug, the ones that zero in on serotonin have side effects. Elavil makes people sleepy. Zoloft can trigger headache and nausea. Zoloft and Prozac may cause sexual dysfunction. All these symptoms are annoying, to be sure, yet they are a price that many sufferers have been willing to pay.