With quasi-religious devoutness, Jenny avoids every crack on the sidewalk, lest she "break her mother's back." Just six years old, she is already a captive to frightening obsessions, a slave to ritualistic compulsions.

Like his father before him, Jeff was a teenager when he took to drink and began his slide into mischief, violence, and depression. Tonight -- unemployed, desperate, and drunk -- he takes a rifle to his wife and children, then to himself.

Every day, Lydia has a new ache, a new pain. They keep her awake at night. They fuel her chronic fatigue and depression. Her doctors say it's all in her head -- and it may be.

A massive body of research suggests these people have at least one thing in common: a deficiency or defect in the behavior of an important messenger molecule in their brains, a neurotransmitter called serotonin.

Of the dozens of neurochemicals that help mediate the complex comings and goings of our minds and behaviors, possibly none has come in for so much scrutiny as serotonin. It has a finger in almost every neurobehavioral pie: impulse control, aggression, sociability, mood, appetite, sleep, pain, and more. Disturbances in the way brain cells called neurons use serotonin to signal other neurons -- typically, deficiencies of "serotonergic" (serotonin mediated) activity -- are proving to be a common denominator among a remarkably broad range of neuropsychiatric disorders. And drugs which boost serotonin -- drugs like the selective serotonin reuptake inhibitors (SSRIs) Prozac, Paxil, and Zoloft -- are proving to be the most versatile agents in the psychiatrist's little black bag.

Long before these medications became household words, a more direct means of boosting serotonin enjoyed widespread popularity: supplements of the nutrients from which serotonin is made. In hundreds of clinical trials, tryptophan and 5-hydroxytryptophan (5-HTP) showed that they often could equal or beat drugs at their own game. And while these supplements have druglike hazards of their own, it is becoming apparent that there are other, generally safer, natural ways of boosting serotonin: herbs, exercise, bright light, and diet, among others. In this book we'll examine all these approaches, but first we'll see what the serotonin connection has to offer for so many of our aches and ills.