NEW YORK (Reuters Health) - Adolescents with anorexia nervosa who also have other psychiatric disorders -- usually depression and anxiety disorders -- do not respond as well to family therapy as those without additional conditions, research shows.

"The presence of these additional problems also increase the likelihood that a family will not stay in family therapy," Dr. James Lock, who led a study to identify predictors of family therapy success, or failure, for adolescent anorexia, told Reuters Health.

"About one third of adolescents with anorexia nervosa suffer from additional psychiatric problems," noted Lock, who is with the department of psychiatry and behavioral sciences at Stanford University in California.

The findings are based on a study of 86 adolescents with anorexia and their families who participated in a study were they were randomly assigned to short- (6 months) versus long-term (12 months) family therapy for adolescents with the eating disorder.

"There is a growing body of evidence that suggests family-based therapy for adolescents with anorexia nervosa is an effective treatment," Lock and colleagues note in the International Journal of Eating Disorders.

"Previous reports suggest that overall the approach is feasible with most families, though demanding," they add.

Other "key observations" from the study, Lock said, was that having problems or conflict within the family was associated with lower anorexia remission rates, as was being assigned to 12 months of family therapy as opposed to 6 months.

On the flip side, the researchers found that younger adolescents generally do better than older ones in family therapy. "And adolescents with anorexia nervosa who gain weight early on in family therapy also tend to do better," Lock said. "Therefore, early response in terms of weight gain bodes well for remission from anorexia nervosa."

The overall remission rate was 68 percent, which is similar to that reported by other studies of family therapy for adolescent anorexia, Lock and colleagues point out.