OPTIMIST is a two-year, randomised, active controlled, open-label, multicentre intervention trial. OPTIMIST includes 3 treatment groups each comprising combinations of romosozumab (ROMO) and zoledronate (ZOL) treatment used in standard doses (210 mg monthly (sc) and 5 mg yearly (iv), respectively). The study will investigate if it is possible to maximize the effect of romosozumab by giving it in 2 periods of 6 months interrupted by zoledronate for 12 months compared to romosozumab for 12 months uninterrupted followed by zoledronate for 12 months. The investigators will also evaluate if 6 months of romosozumab followed by 18 months of zoledronate is non-inferior to the standard regimen of romosozumab for 12 months followed by zoledronate for 12 months.