For the first time, a study has shown that high doses of steroids actually can help a person build muscle size and strength without causing side effects over the short term.

However, several researchers cautioned that the findings do not give the green light for athletes, recreational bodybuilders and others to abuse anabolic/androgenic steroids.

In the 10-week study of 43 men, those who participated in a weight-training program and received weekly injections of testosterone enanthate--600 mg-- increased their muscle mass and strength substantially compared with those who lifted weights regularly but did not take steroids.

And no negative effects were observed on mood or behavior in the men taking testosterone, the study authors reported in The New England Journal of Medicine (1996; 335:1-7).

"Our results in no way justify the use of steroids in sports, because such drugs have potentially serious adverse effects," wrote lead researcher Shalender Bhasin, M.D., of the Charles R. Drew University of Medicine and Science in Los Angeles.

However, steroids may be beneficial for the short-term treatment of patients with cancer-related cachexia, disease caused by HIV or other chronic wasting disorders, he said.

Previous research in humans used doses of steroids that were too small to show the drugs' effects on muscle, making the new study the first to prove what athletes have been saying for years, C. Wayne Bardin, M.D., of the National Institute of Child Health and Human Development in Bethesda, Md., wrote in an accompanying editorial.

"The fact that a large dose of testosterone did not affect serum concentrations of lipids and prostate-specific antigen levels or measures of mood and behavior should provide some short-term reassurance," he wrote.

Dr. Bhasin and colleagues compared muscle size, strength and fat-free body mass in men who received testosterone alone, testosterone plus exercise, placebo alone or placebo combined with exercise.

The men in the testosterone-plus-exercise group gained about 13.5 pounds of fat-free mass, and their triceps and quadriceps increased substantially in size compared with the men in the other groups, the study showed.

In addition, muscle strength in squatting exercises increased by about 38% and bench-press strength improved by about 22% in the men who exercised and received steroid injections. These improvements were markedly greater than the other groups, the researchers wrote.

"But [this] doesn't change doctors' bent on steroid use," said Peter Bruno, M.D., the internist for the New York Knicks basketball team.

Steroid use is still not appropriate for all of the 18- to 25-year-old athletes who take high doses of steroids for prolonged periods of time, Dr. Bruno said.

"The bottom-line is that short-term supraphysiologic doses of testosterone enanthate are well-tolerated without dramatic side effects," said William Bremner, M.D., vice chairman of the University of Washington School of Medicine in Seattle.