A 2005 federal law classified "pro-hormones," or steroid precursors, as controlled substances, essentially banning them from diet supplements sold over the counter.

That greatly reduced the risk of positive tests with those products, said Frank Uryasz, president of the National Center for Drug Free Sport, which conducts drug testing for the NCAA and other organizations.

Teenagers may be drawn to supplements to gain weight or add muscle, and concerns they could be snagged by Texas' new high school steroids testing program caused alarm and disagreement among lawmakers on whether to delay the start.

Gov. Rick Perry, who signed the program into law last month, urged caution even if it meant waiting until after football season to begin testing.

But Uryasz said the 2005 law greatly reduced the risk of banned substances showing up in store products.

"I think it's much less of a concern than it was a few years ago," he said.

The greater risk is for athletes who purchase products over the Internet or on the street. The risk of those products containing steroids are much higher, Uryasz said. He urged young athletes to avoid supplements altogether.

"They don't need them, and they're expensive," he said.

Sen. Kyle Janek, one of the authors of the law, agreed.

"It's just insane for kids to be buying this stuff off the Internet," Janek said. "If somebody says it will make you bigger, stronger and faster and will pass the drug test, don't believe it."

The 2005 law added 18 substances to the list of banned anabolic steroids. The law was aimed at steroid precursors, which metabolize into steroids once they are ingested. The list includes androstenedione, commonly known as "andro" and made famous by Mark McGwire a decade ago when he broke baseball's record for home runs in a season.

"We see much fewer positives for many of those compounds," Uryasz said. "We also hear fewer appeals that a positive test was caused by a banned substance in a dietary supplement."

The NCAA warns its athletes that diet supplements may contain banned products and that athletes assume all risk if taking one.

The warning is also geared toward stimulants that may show up in supplements but are not included in the Texas testing program.

Texas, New Jersey and Florida are the only states to conduct mandatory, random steroid tests of high school athletes. The Texas program would be the largest, targeting about 22,000 students a year from the pool of more than 700,000 public school athletes in all sports.

It is unclear when the Texas program will start, although it will be sometime this fall.

Contractors have until July 27 to bid for the two-year, $6 million program run by the University Interscholastic League, the governing body of Texas public school sports.

Public high schools start football practice Aug. 6 and play their first games Aug. 30. The first volleyball matches are Aug. 13.

"We haven't set any firm timetable," said Mark Cousins, UIL athletic coordinator. "We're going to make sure we do it right. We will get the program going as quickly as we can."

Even if testing hasn't started, athletes must submit a signed form acknowledging they could be tested for steroids before they will be allowed to play in a game.