Berahino joined Stoke in January for a reported £12m having not played for former club West Brom since September 2016.
West Brom manager Tony Pulis had said repeatedly that the striker was not playing because of a lack of fitness.
"I still don't know who would do this to me," Berahino said in an interview with the BBC. "To be banned for something you haven't done is hard to take."
Berahino said he had never taken drugs and that the levels found in his body were "really low".
Read the full article on eurosport.co.uk: Stoke City striker Berahino says spiked drink led to ban