- Subjects currently undergoing the following concomitant therapy: radiotherapy, pain inducing chemotherapy, anti-parkinsonian drugs, neuroleptics, monoamine oxidase inhibitors, serotonin norepinephrine re-uptake inhibitors (SNRI) or any other analgesic therapy than investigational medication or rescue medication during the trial. Selective serotonin re-uptake inhibitor (SSRI) treatments are allowed if taken for at least 30 days before the screening period of the trial at an unchanged dose.