The choice of anti-inflammatory prophylaxis parallel to cataract surgery is important for patient safety and successful outcome of surgery, but which regimen to choose is contested. To determine whether a combination of prednisolone and nonsteroidal anti-inflammatory drug (NSAID) eye drops was superior in preventing increased central macular thickness (central subfield thickness [CST]) after uncomplicated cataract surgery compared with NSAID monotherapy and sub-Tenon capsule depot (dropless surgery), and to test whether preoperative initiation of eye drop treatment was superior to initiation on the day of surgery. This investigator-driven, single-center, randomized clinical trial with masked statistical analyses enrolled patients at the Department of Ophthalmology, Rigshospitalet Glostrup, Glostrup, Denmark, from February 1, 2018, to August 15, 2019. Follow-up was completed December 18, 2019. Participants included low-risk patients undergoing phacoemulsification for age-related cataract by an experienced surgeon (1 eye per participant). Data were analyzed from February 17 to June 15, 2020. Participants scheduled for cataract removal were randomized to 1 of 5 anti-inflammatory prophylactic regimens: eye drops with a combination of prednisolone, 1%, and ketorolac tromethamine, 0.5%, with or without preoperative initiation (preoperative prednisolone plus NSAID [control] and postoperative prednisolone plus NSAID groups), ketorolac monotherapy with or without preoperative initiation (preoperative and postoperative NSAID groups), or sub-Tenon depot of dexamethasone phosphate (sub-Tenon group). Eye drops were administered 3 times per day until 3 weeks postoperatively. CST 3 months postoperatively. A total of 470 participants (mean [SD] age, 72.2 [7.0] years; 290 women [61.7%]) with 94 participants in each group were included in the analysis. Three months after surgery, the mean CST was 250.7 (95% CI, 247.6-253.7) μm in the preoperative prednisolone plus NSAID group, 250.7 (95% CI, 247.8-253.7) μm in the postoperative prednisolone plus NSAID group, 251.3 (95% CI, 248.2-254.4) μm in the preoperative NSAID group, 249.2 (95% CI, 246.2-252.3) μm in the postoperative NSAID group, and 255.2 (95% CI, 252.0-258.3) μm in the sub-Tenon group. There were no significant differences in CST or visual acuity compared with control and no differences between preoperative and postoperative groups, but 47 of 83 participants (56.6%) in the sub-Tenon group needed additional anti-inflammatory treatment. No differences in CST or visual acuity were detected between the combination of prednisolone and NSAID eye drops vs NSAID monotherapy or sub-Tenon dexamethasone depot, although more than one-half of patients in the sub-Tenon arm received additional anti-inflammatory treatment. Initiating prophylaxis 3 days preoperatively was not superior to initiation on the day of surgery. Monotherapy with NSAIDs may be preferred in uncomplicated cataract surgery. ClinicalTrials.gov Identifier: NCT03383328.