Günther was sent home from a training camp in Ukraine and suspended until further notice once the Swedish Wrestling Association was told about the positive test.
“It was only eight or nine days left until the European Championships and since I had finally been given a spot on the national team I wanted to get well before the competition,” Gunther told Swedish Radio.
“I never thought that the pill I took might have contained banned substances, not even when I took the test.”
Günther was preparing to qualify for the 2012 London Olympics.
“This is a personal tragedy for Mathias and not a fun position to be in for the sport,” said Benni Ljungbäck, head of the Wrestling Association.