As many as 500,000 U.S. high school boys have taken anabolic steroids, most trying to boost football and wrestling performance, but others seeking to improve their appearance with the potentially dangerous drugs, a study said this week.

In the first nationwide investigation of use of anabolic steroids among high schoolers, researchers found 6.6 percent of 12th-grade males said they had taken or were taking anabolic steroids, many starting the drugs while they were in junior high school."I was surprised. That's about twice what I had expected, and even this (steroid use) may have been slightly under-reported," said William Buckley, an assistant professor of health education at Pennsylvania State University's College of Health and Human Development, who led the study. "It's a significant pattern of use."

The study, reported in the Journal of the American Medical Association, anonymously surveyed 3,403 male seniors at 46 public and private schools across the country.

The researchers said if the 6.64 percent use rate "is applied to the national population of males enrolled in secondary schools, it suggests that between 250,000 and 500,000 adolescents in the country have used or are using these drugs."

This is worrisome, Buckley said, because little is known about effects of anabolic steroids taken before or during puberty. Taken to enhance muscle growth during athletic training, the drugs can stunt stature and growth of long bones. In addition, steroids may contribute to acne, accelerate body hair growth and lead to breast growth.

Adults taking the drugs may at least temporarily produce abnormal sperm, and have decreased testical size and sex drive, but Buckley said reproductive consequences are unknown for youngsters.

In addition, doctors have reported cholesterol, kidney and liver problems, including cancer, in adults taking the drugs, but these effects have not been studied in teenagers.

Buckley said he was particularly worried by evidence linking anabolic steroids to aggressive behavior in adult users. "If the same holds true in this age group, as kids are starting to develop problem-resolution skills, if this agression comes to the forefront, they're really not learning those coping skills as effectively as they might and may well may carry that the rest of their lives," Buckley said.