Opioid painkillers like codeine can result in constipation and will make you are feeling sick. They may also make you drowsy, so don’t consider an opioid painkiller if you must drive or function machinery.CYP3A4 inducers, for example rifampicin, carbamazepine, phenytoin and St John's Wort might induce the metabolism of oxycodone and induce an ele