CHICAGO - Children and teens with attention deficit hyperactivity disorder fared no better on St. John's wort than they did on dummy pills in a government study, another blow for herbal supplements.

St. John's wort, pine bark extract, and blue-green algae are among commonly used herbal treatments for children with ADHD. They appeal to parents who want to avoid stimulants like Ritalin and other drugs to help children control their behavior.

But unlike prescription drugs, supplements are only loosely regulated by the government and their makers do not have to prove they are safe or effective.

"Do an Internet search and you'll find a wide variety of herbal products marketed for ADHD," said lead author Wendy Weber of Bastyr University's School of Naturopathic Medicine outside Seattle. "I've found there is very little research on the majority of products out there."

Weber, working with colleagues at Harvard University and the University of Washington, focused on St. John's wort because studies in rats found it increased brain chemicals like norepinephrine, believed to help focus attention.

Weber reasoned St. John's wort might work the same way as the prescription drug Strattera, approved by the Food and Drug Administration to treat ADHD. Strattera makes norepinephrine more available in the brain.

In the study, in today's Journal of the American Medical Association, 54 children with ADHD were randomly assigned to take either St. John's wort capsules three times a day or placebos. They ranged in age from 6 to 17 years old.

Symptoms were measured at the start of the study and four other times. After eight weeks, the two groups showed no difference in symptoms or side effects.

Adriana Arjona, a 15-year-old diagnosed with ADHD several years earlier, took part in the study in the Seattle area. She has never taken prescription medication for the condition because her mother, Aracelly Salazar, believes the potential side effects of nervousness, agitation and insomnia are worse than her daughter's symptoms.

St. John's wort didn't seem to have much effect, both mother and daughter agreed. The teenager learned after the study ended that she had taken the supplement, not the dummy pill.

The study's results should give pause to parents who have avoided well-researched prescription medicines in favor of herbal remedies, said Dr. Eugenia Chan of Children's Hospital Boston, who was not involved in the new research.