BALTIMORE (AP) – Depending on whom you ask, Rafael Palmeiro’s claim that he unwittingly took something to cause a positive test for steroids is either plausible – or laughable.

The lack of regulation and testing of nutritional supplements lends credence to the claims of players who say they were caught unaware by positive tests, one researcher said Tuesday.

Steroid building blocks known as prohormones can cause a positive test – and may not be listed on supplement labels, said Anthony C. Tommasello, a professor and director of the Office of Substance Abuse Studies at the University of Maryland pharmacy school in Baltimore.

“Some are extracts of natural products that are also metabolized into anabolic hormones but the substances are not on the banned list,” Tommasello said.

One such ingredient is DHEA, Tommasello said. Mostly manufactured in China from the dried roots of a wild yam, it is a popular muscle-building supplement in the United States. While not on Major League Baseball’s list of banned substances, it is converted in the body into an anabolic steroid, Tommasello said.

If Palmeiro knew he was taking the so-called precursors, it’s akin to steroid use, said Adrian Dobs, an endocrinologist and professor of medicine at Johns Hopkins University in Baltimore. “These people aren’t dumb. They know what they are doing,” she said.

Palmeiro – who testified before a congressional panel in March that he “never used steroids” – became baseball’s highest-profile player to serve a 10-game suspension Monday after testing positive for a performance-enhancing drug. And while he didn’t deny turning in a positive test, the slugger was adamant that it was an accident.

“When I testified in front of Congress, I know that I was testifying under oath and I told the truth,” he said during a telephone conference call Monday. “Today I am telling the truth again that I did not do this intentionally or knowingly.”

And at least one member of baseball’s management-union medical panel initially found there was a “reasonable basis” for Palmeiro’s claims, as evidenced by the delay in his penalty.

But the notion that a legal, nonprescription supplement could cause a positive test for steroids doesn’t make sense to David R. Seckman, executive director of the National Nutritional Foods Association, which represents the supplement industry.

While looking over baseball’s list of banned substances, Seckman was unequivocal in saying that the average nutritional supplement store “isn’t selling those type of products.”

“Those are steroids. They are controlled substances,” Seckman said. “You can only get those with a prescription.”

Nor does he believe the problem could lie in mislabeling: Over-the-counter dietary supplements are required by law to list each ingredient on the label, Seckman said, adding that the chances of them being contaminated are “infinitesimal.”

However, Tommasello cited a German study found almost 15 percent of 634 supplements tested from 13 countries (including the United States) and 215 suppliers contained steroids not listed on the label.

Palmeiro was the seventh player to fall under baseball’s new, tougher steroids policy; Seattle Mariners right-hander Ryan Franklin became the eighth when he was also suspended 10 days for a violation Tuesday. Baseball does not release what type of drug a player has tested positive for, and so far none of the eight have spoken openly about details of their violations.

Fellow players were mixed on the credibility of Palmeiro’s claims.

“It’s a shame,” said Atlanta Braves outfielder Brian Jordan. “He’s been in front of Congress. It’s another shock to the game of baseball. … He’s accomplished some great things and now he’s going to have to answer some serious questions.”

Chicago White Sox catcher A.J. Pierzynski expressed sympathy for Palmeiro, who last month joined Hank Aaron, Willie Mays and Eddie Murray as the only players with 3,000 hits and 500 homers.

“He could have been taking a supplement over the counter. Sometimes things get mixed up,” Pierzynski said. “That’s one thing the union has really tried to address with us, is that you don’t know what’s in supplements. You have to be real careful.”

Manufacturers are responsible for ensuring the safety of dietary supplements, but generally do not need FDA approval to produce or sell them.

. Tommasello said that lack of regulation should raise concerns – especially considering problems with regulated drugs such Vioxx, a painkiller later found to be linked to increased risk of heart attack, which are well studied.

“We know pretty much what drugs are going to do to people, what the side effects are and the risk and even at that, we have problems,” Tommasello said. “I don’t think we know clearly what these chemicals (supplements) are doing to people.”

Baltimore Ravens coach Brian Billick called the issue his “biggest concern.”

“The combination of this and that, what’s actually in it, you’re trying to do the right thing, you’re trying to take legal supplements to take care of your body and it is so unregulated,” Billick said. “That is a major concern of mine, but that’s a societal concern, not just a football concern.”

Because of the confusion, the National Football League and its players union announced a program two years ago to certify supplements as free of banned substances and Major League Baseball is also looking into a similar program.

Tommasello, however, said his experience in drug testing has shown him that it is not an easy task. “People say they got a false positive (for opiates) because they ate poppy seeds,” he said, noting such claims were at first dismissed, then found to sometimes be true after further testing.

Washington Nationals outfielder Brad Wilkerson, who has said he used creatine and protein powders in the past, isn’t taking any chances in baseball’s current climate.

“A lot of guys have limited what they’re taking,” Wilkerson said Tuesday. “I really don’t take anything anymore. I really don’t know what’s in what.”