Weight wars: hormones/metabolism.

Want biceps to rival The Rock's? You're not alone. The thirst for bulging muscles is on the rise--and so is the use of anabotic steroids, illegal and dangerous muscle-building drugs. "More than 500,000 eighth-and tenth-graders now use steroids," says Alan Leshner, director of the National Institute on Drug Abuse.

Anabolic steroids--high doses of the male sex hormone testosterone--increase lean muscle mass. The drugs signal young body cells to rapidly mature into muscle cells rather than fat cells. But getting ripped with steroids comes with a big price for boys: side effects like shrunken testicles, breast development, acne, premature balding, uncontrolled aggression, even death. Girls who take steroids can develop permanent facial hair and deepened voices. Worth it?

DYING TO BE THIN While thousands of American teens are obsessed with becoming buff, another 5 to 10 million are starving themselves, according to the National Institute of Mental Health. The condition is called anorexia nervosa. "One study shows that young girls are more frightened of being fat than they are of their parents dying or a nuclear holocaust," says Dr. Ira Sacker, head of the Eating Disorders Clinic at Brookdale University Hospital and Medical Center in Brooklyn, New York.

Anorexics deeply fear gaining weight, so they don't eat enough. But the body demands food for energy, to build tissue, and--above all--to survive. Adequate food intake is especially critical during the teen years. "You experience your second-fastest growth spurt during puberty," says psychologist Sylvia Rimm, author of See Jane Win. "You need nutrients to feed that growth."

To learn more about eating disorders, visit

www.nationaleatingdisorders.org.