"I was horrified when I got the test results and once we tracked back and worked out I had inadvertently taken the wrong tablet... ," Johnson said in a statement on Wasps' website.
"I am now working hard in pre-season and am looking forward to putting this behind me and getting back to being part of the Wasps squad."
Wasps begin their Premiership campaign at Worcester on Sept. 1.
(Reporting by Aditi Prakash in Bengaluru; Editing by Peter Rutherford)
