Background: Efficacy of combination therapy with methotrexate and biological disease-modifying antirheumatic drugs is well established in the management of patients with rheumatoid arthritis; however, the optimal dose of methotrexate to administer with a tumour necrosis factor inhibitor remains unclear. We aimed to clarify the efficacy and safety of adalimumab combined with reduced methotrexate dose compared with the maximum tolerated methotrexate dose in patients with rheumatoid arthritis and an inadequate response to methotrexate monotherapy., Methods: In this open-label, randomised controlled trial, we recruited methotrexate-naive patients with rheumatoid arthritis and a disease duration of less than 2 years across 24 secondary or tertiary care hospitals across Japan, South Korea, and Taiwan. At initiation, methotrexate was given orally and increased to the maximum tolerated dose by week 12. Patients who did not achieve remission on the basis of the Simplified Disease Activity Index (SDAI) at week 24 were randomly assigned (1:1) to receive adalimumab (40 mg biweekly) combined with a continued maximum tolerated dose of methotrexate or adalimumab combined with a reduced dose of methotrexate. The primary endpoint was non-inferiority of adalimumab plus reduced-dose methotrexate to adalimumab plus maximal-dose methotrexate based on SDAI remission at week 48, assessed in the modified full-analysis set with a pre-specified non-inferiority margin of -15%, based on a two-sided 90% CI. Adverse events were assessed in the safety analysis set. This trial is registered with ClinicalTrials.gov, NCT03505008 and has been completed., Findings: From April 18, 2018, to June 2, 2020, from 323 patients screened, 300 were enrolled, and 291 patients were included in the full analysis set. The mean age was 57·7 years (SD 15·2), 217 (75%) were female, 74 (25%) were male, and all patients were of Asian ethnicity. The mean SDAI at study enrolment was 26·5 (SD 12·4). 52 patients discontinued the study before week 24 or at week 24 before randomisation. At week 24, 105 (36%) of 291 patients achieved remission and continued methotrexate monotherapy through week 48. 134 (46%) did not achieve remission at week 24 and were randomly assigned to receive adalimumab plus the maximum tolerated dose of methotrexate (n=68) or adalimumab plus reduced-dose methotrexate (n=66). Remission at week 48 was achieved in 25 (38%) of 66 and 27 (44%) of 61 patients, respectively, with an adjusted risk difference of 6·4% (90% CI -7·0 to 19·8), which met the non-inferiority margin of -15%. Adverse events after week 24 tended to be more frequent in the maximum tolerated dose group than in the reduced-dose group (24 [35%] vs 13 [20%], p=0·054). Between week 24 and 48, there were 14 serious adverse events (6 in the methotrexate monotherapy group, 5 in the adalimumab plus maximal-dose methotrexate, and 3 in the adalimumab plus reduced-dose methotrexate group), and no deaths., Interpretation: The MIRACLE study showed that the efficacy of adalimumab combined with reduced methotrexate dose was not inferior to that with the maximum tolerated methotrexate dose, with a tendency to a better safety profile., Funding: Eisai., Competing Interests: Declaration of interests HTam has received speaker honoraria from AbbVie and Eisai. KI has received grants from Mitsubishi-Tanabe Pharma, speaker honoraria from AbbVie, Eisai, Mitsubishi-Tanabe Pharma, Astellas Pharma, UCB, Daiichi-Sankyo, Eli Lilly, Gilead Sciences, Asahi Kasei Pharma, Chugai Pharma, and Bristol-Myers Squibb. TM received grants, research support, or speaker fees from AbbVie, Astellas Pharma, AstraZeneca, Bristol-Myers Squibb, Chugai Pharma, Daiichi-Sankyo, Eisai, Eli Lilly, Gilead Sciences, Kirin, Pfizer, and UCB. KS has received grants, research support from Novartis, Astellas Pharma, AbbVie, Bristol-Myers Squibb, and Yuhan Corporation, and consulting fees from KD Bio. SH has received grants from AbbVie, Asahi Kasei Pharma, Eisai, Otsuka, Sanofi, Shionogi, Chugai, Pfizer, Mitsubishi-Tanabe Pharma, Eli Lilly, and UCB; speaker honoraria from AbbVie, Asahi Kasei Pharma, Astellas Pharma, Ayumi Pharma, Bristol-Myers Squibb, Celgene Corporation, Chugai Pharma, Eisai, Gilead Sciences, GlaxoSmithKline, Eli Lilly, Janssen, Kyorin Pharmaceutical, Novartis, Pfizer, Sanofi, Mitsubishi-Tanabe Pharma, and UCB; paid instructor fees from AbbVie and Mitsubishi-Tanabe Pharma; and consulting fees from AbbVie, Astellas Pharma, Bristol-Myers Squibb, Eisai, Gilead Sciences, and Eli Lilly. SS has received grants from Asahi Kasei Pharma, AbbVie, Chugai Pharma, Eli Lilly, Eisai, Teijin, Pfizer, Ayumi Pharma, and Daiichi Sankyo. HY has received research grants from Asahi Kasei Pharma, Mitsubishi-Tanabe Pharma, Chugai Pharma, Eisai, and Taisho Pharma; speaker fees from AbbVie, Janssen, Gilead Sciences, Nippon Boehringer Ingelheim, and Nippon Shinyaku. MK has received grants from Nippon Boehringer Ingelheim, Ono Pharma, and MBL; royalties from MBL; consulting fees from Nippon Boehringer Ingelheim, Mochida Pharmaceutical, and Kissei Pharmaceutical; speaker honoraria from AbbVie, Asahi Kasei Pharma, Astellas Pharma, Chugai Pharma, Nippon Shinyaku, Mitsubishi-Tanabe Pharma, and Nippon Boehringer Ingelheim. TI has received payment or honoraria from AbbVie, Asahi Kasei Pharma, Astellas Pharma, Bristol-Myers Squibb, Chugai Pharma, Eisai, Eli Lilly, Gilead Sciences, Janssen, Pfizer, Boehringer Ingelheim, Novartis, and GlaxoSmithKline. HK has received a research grant from AbbVie, Asahi Kasei Pharma, Boehringer, Chugai Pharma, Eisai, Mitsubishi-Tanabe Pharma, and Taisho; speaker honoraria fees from AbbVie, Asahi Kasei Pharma, Astellas Pharma, Boehringer, Bristol-Myers Squibb, Chugai Pharma, Eisai, Eli Lilly, Gilead Sciences, Janssen, Mitsubishi-Tanabe Pharma, Novartis, Pfizer, and UCB. TK has received grants or research support and speaker fees from AbbVie, Astellas Pharma, Bristol-Myers Squibb, Chugai Pharma, Daiichi-Sankyo, Eli Lilly, Pfizer, Eisai, UCB, and Taisho. TTan, MM, and HM are shareholders and employees of Eisai. YS has received speaker honoraria from Eisai and Kowa Pharmaceuticals; and consulting fees from Mochida Pharmaceutical. TTak received grants from AbbVie, Asahi Kasei Pharma, Ayumi Pharma, Chugai Pharma, Eisai, Eli Lilly, Mitsubishi-Tanabe Pharma, and Ono Pharma; consulting fees from AbbVie, Chugai Pharma, Eli Lilly, and Gilead Sciences, and Mitsubishi-Tanabe Pharma; and payment or honoraria from AbbVie, Asahi Kasei Pharma, Astellas Pharma, Bristol-Myers Squibb, Chugai Pharma, Daiichi-Sankyo, Eisai, Eli Lilly, Gilead Sciences, Janssen, Mitsubishi-Tanabe Pharma, and Pfizer. YK has received grants from AbbVie, Asahi Kasei Pharma, Ayumi Pharma, Chugai Pharma, Eisai, Mitsubishi-Tanabe Pharma, Boehringer Ingelheim, and Asahi Kasei Pharma; payment or honoraria from AbbVie, Asahi Kasei Pharma, Astellas Pharma, Bristol-Myers Squibb, Chugai Pharma, Daiichi-Sankyo, Eisai, Eli Lilly, Gilead Sciences, Janssen, Mitsubishi-Tanabe Pharma, Pfizer, Boehringer Ingelheim, Asahi Kasei Pharma, and Novartis. All other authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)