CHICAGO — Children and teenagers 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 used to help children control their behavior.

But unlike prescription drugs, supplements are only loosely regulated by the government and their makers don’t 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,” the lead author, Wendy Weber of Bastyr University’s School of Naturopathic Medicine in suburban Seattle, said. “I’ve found there is very little research on the majority of products out there.”

Ms. Weber, working with colleagues at Harvard University and University of Washington, focused on St. John’s wort because studies in rats found it increases brain chemicals like norepinephrine, which is thought to help focus attention.

Ms. 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, appearing 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 between six and 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 standard 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.

Earlier this year, the American Heart Association recommended that children should be screened for heart problems before getting drugs like Ritalin. That increased parents’ anxieties about the drugs, Dr. Chan said.

But “natural” doesn’t mean risk-free. St. John’s wort can increase sensitivity to the sun and reduces the effectiveness of some medications, including birth control pills.

ADHD affects more than 4.4 million children, according to government estimates.

Dr. Chan, who has studied the use of alternative medicines in ADHD, found that more than half of parents of ADHD children had tried alternative treatments and special diets, but only 11% had told their children’s doctors about those strategies. She wrote an accompanying editorial in the journal.

The research follows other studies with disappointing results for alternative remedies such as echinacea for the common cold, saw palmetto for prostate problems, and glucosamine and chondroitin for arthritis pain.

It was funded by a grant from the National Center for Complementary and Alternative Medicine, part of the National Institutes of Health.