My Friend Had An Over Dose And Had Cpr Done

My friend had an over dose and had cpr done he's quite husky around 280 lbs and is 54 years old he was taken to the hospital and x-rayed and does not have any broken ribs but still two weeks later has a lot of soreness in his chest and coughing bothers him quite a bit. Do you know what would cause this uncomfortable pain and what he should do about it?
Would this be due to his sternum being pushed out of place during CPR?