Redskins linebacker Rob Jackson said he was frustrated by the situation that led to him receiving a four-game suspension to start the 2013 season, but that all he can do now is focus on football and prepare so he is ready to make an impact when he can. It was learned during the offseason that Jackson had earned a suspension for taking an unapproved painkiller — which he now reveals was Codeine — during the 2012 season. Jackson was bothered by a bad tooth and took the pills, which were prescribed to his girlfriend, and not himself. Jackson, who until Thursday, hadn’t spoken to reporters about the suspension, said the day after he took the pills, he was selected for a random drug test. But he says he never thought that he had done something wrong. “I didn’t until I got the letter, and then I was like, ‘Codeine?’ then I thought, ‘okay, it makes sense now,’” recalled Jackson, who had the tooth pulled. Initially, he thought he had a good chance to fight the suspension and win the appeal. “I thought I had a chance to, because I showed them all the papers and all the doctors notes to show I did have work done, but at the time, the pills weren’t prescribed to me, so,” he said. It was very frustrating, just the way things happened: me taking the pills for the pain, the next day me being tested, a couple weeks later, me getting a letter. But I feel that everything happens for a reason. I’m a firm believer in that.” Jackson had a career season last year, starting 14 games, recording 4.5 sacks and four interceptions — one of which he returned for a touchdown. He was a restricted free agent this past offseason, but re-signed with Washington on a one-year deal worth $715,000.