Dustin Richardson, the 26-year-old left-handed pitcher, had tested positive and been suspended for 50 games, a result that a spokesman for Major League Baseball acknowledged was “unusual.”

“I’ve never seen a case like this, and we’re talking about 30 years I’ve been doing this kind of work,” said Don Catlin, an anti-doping expert and former director of the U.C.L.A. Olympic Analytical Laboratory.

“I’ve had doublets and triplets, but to have five, and have it cover three different subclasses of drugs, is unique, as far as I can tell,” Catlin added.