Armitage, 26, won the first of his five caps for England during the 2009 RBS 6 Nations against Italy but effectively ruled himself out of adding to his tally by signing for Toulon from London Irish in 2011.
Across the channel Armitage has thrived on the field and there was clamour for him to be included in England head coach Stuart Lancaster's touring party to South Africa this June.
But on June 9 morphine was found in a sample following Toulon's loss to Toulouse and Armitage is due to appear before the French rugby anti-doping commission on August 21.
The openside flanker is confident, however, that he has not committed any wrongdoing.
"It's a bit stressful, especially for my family in England," said Armitage. "But I will keep my head held high because I have done nothing wrong.
"I know that everything will soon be sorted, that I will be able to forget about this and come back stronger."
Toulon have backed Armitage stating that the positive result was caused by a combination of painkillers and anti-inflammatories which he had taken for back pain.
"Before the game, Steffon Armitage took two tablets of paracetamol codeine, a medicine strictly authorised by the French Agency for the Fight against Doping (AFLD)," read a club statement.
"Having suffered with back pain in the week leading up to the game, Steffon Armitage was given anti-inflammatories as well as paracetamol codeine (two to four tablets per day) for these pains. All of the medicines administered are authorised by the AFLD."