"We continue to work with the Association in identifying what should be on the banned list," said Pat Courtney, MLB's vice president of operations. "We jointly make sure players are aware.
"We're continually reviewing that list, and update it regularly with ordinary products known to cause false positives."
The MLBPA distributed the latest list on Tuesday to its playing union members, as well as the training staffs of the 30 Major League teams.
"It lists substances that the FDA [Federal Drug Administration] has identified as able to trigger positive tests for a banned substance," said Ned Bergert, the Los Angeles Angels' longtime head athletic trainer. "Everything with that potential is on that list."
Claims of inadvertent intake of contaminated products are not uncommon by athletes, in baseball and in other sports, who had tested positive for banned performance-enhancing drugs.
"The burden of proof then falls on the players," Bergert said. "They are all adults, and need to be aware of what they're ingesting.
"When I get the list, I place a copy of it in their lockers, and also e-mail copies to them and to their agents. Players should take only supplements that are NSF-certified for sports. Tests on anything else will come back as a banned substance."
NSF is a sports consulting and advisory firm whose certification of health products is recognized as the industry standard. Acceptable products carry the NSF logo.
"We work through NSF. Anytime we come across new information through them, or another laboratory or, really, anyone reliable, we update this list," Courtney said.
Several players questioned about the latest list, and on the guidance it provides, chose to not comment.
But Dodgers outfielder Reed Johnson called the list "something that can help you muddle through all the supplements out there."
"You can never be too careful," Reed said. "There's other things we can do -- like if you're not sure about something, you can send a sample to the union and they'll check it out for you -- but I'd sure hate to get caught for something I took from GNC. You always want to do the right thing."
It is not known whether any supplements on the updated MLBPA list have triggered false positives in the past.