 Patients in the intervention group will receive regular clinical care and morphine SR 10mg, administered twice daily 20mg24h, which can be increased after one or two weeks to three times per day 10mg 30mg24h in non-responders. Patients will be defined as non-responders if the mean dyspnea numeric rating scale NRS score was not reduced by 1 point in comparison with baseline. The control group will receive regular clinical care and placebo medication. Patients will receive morphine or placebo for four weeks. In addition, both groups will receive a prescription for a laxative and metoclopramide at the start of the intervention and will be instructed to adjust the dose as needed. 