Background: Patients undergoing total knee arthroplasty (TKA)/ total hip arthroplasty (THA) still experience moderate-severe postoperative pain despite optimized pain management regimes. The patients already on opioid treatment and pain catastrophizers (PCs) have a higher risk of postoperative pain. The use of preoperative intravenous high-dose glucocorticoids decreases postoperative pain after TKA and THA, but optimal dose is yet to be found, and the effect on subpopulations at high pain risk is unknown. Aim: To investigate the effect of a higher than previously used dose of glucocorticoids (dexamethasone (DXM)), administered intravenously before surgery, as part of standardized fast-track regimen, on postoperative pain in TKA/THA subgroups. Method: Three separate randomized, double-blinded, controlled trials were planned to compare a new higher dose DXM (1 mg/kg) to the earlier used high-dose DXM (0.3 mg/kg). Study 1: predicted Low Pain TKA; study 2: predicted High Pain Responder (HPR) TKA; study 3: predicted HPR THA. Predicted HPR groups consist of either PCs with PCS-score of ≥ 21 and/or history of ongoing opioid-treatment of 30 mg/day of morphine or equivalents > 30 days. In total, 408 patients were planned for inclusion (160 Low Pain TKA, 88 HPR TKA, 160 HPR THA). Primary outcome : Pain upon ambulation in a 5-meter walk test 24 hours after surgery. Secondary outcomes include use of analgesics, rescue-opioids, antiemetics, cumulated pain, CRP, OR-SDS, QoR-15, quality of sleep, length of stay (LOS), reasons for hospitalization, readmission, morbidity, and mortality. Patients completed follow-up on day 90. Recruiting commenced February 2019 and is expected to finish in September 2020.