Background: While evidence supports using sustained release morphine for chronic refractory breathlessness, little is known about the longitudinal pattern of breathlessness intensity as people achieve symptomatic benefit. The aim of this study is to describe this pattern. Methods: This secondary analysis used breathlessness intensity scores (100 mm visual analogue scale (VAS)) from a prospective, dose increment study of once daily (morning) sustained release morphine for chronic refractory breathlessness. Participants who achieved <10% improvement over their own baseline at one week (10 mg) were titrated to 20 mg and if no response, another week later to 30 mg for one week. Time was standardized at the first day of the week in which participants responded generating twice daily data one week either side of symptomatic benefit. Analysis used random effect mixed modeling. Results: Of the 83 participants, 17/52 responders required >10 mg: 13 participants (20 mg) and 4 (30 mg), contributing 634 VAS observations. In the week leading to a response, average VAS scores worsened by 0.3 mm/day (p=0.16); the average improvement in the first 24 hours of response was 10.9 mm (7.0 to 14.7; p<0.0001), with continued improvement of 2.2 mm/day (p<0.001) for six more days. Conclusion: When treating chronic refractory breathlessness with once daily sustained release morphine, titrate to effect, since inadequate dose may generate no response; and following an initial response, further dose increases should not occur for at least one week. Whether further benefit would be derived beyond day six on the dose to which people respond, and what net effect a further dose increase would have are questions yet to be answered.