Aim Rheumatoid arthritis (RA) is the most widespread inflammatory arthropathy, which causes severe disability. It is highly important to ameliorate the side effects caused by different drugs used to treat RA. Therefore, this study assessed the potential role of β-caryophyllene (BCP) in treating adjuvant-induced arthritis (AIA), increasing the efficacy of methotrexate (MTX) and/or leflunomide (LEF), and ameliorating their side effects. Material and methods AIA was induced in rats by injecting complete Freund’s adjuvant. The rats were divided into different groups such as sham group; control group; monotherapy groups, including BCP (300 mg/kg), MTX (1 mg/kg), and LEF (10 mg/kg); and combined groups, including MTX+BCP, LEF+BCP, MTX+LEF, and MTX+LEF+BCP groups. Key findings Monotherapy with BCP or MTX or LEF as well as MTX+LEF significantly reduced paw thickness and arthritic index; the histopathological changes in hind paw joints were recovered; and oxidative stress and tumor necrosis factor-alpha (TNF-𝛼) levels in arthritic rats were reduced. The co-administration of BCP and MTX and/or LEF significantly improved the therapeutic efficacy of MTX and/or LEF and significantly reduced the myelosuppressive and hepatotoxic effects of MTX and/or LEF. Taken together, BCP could be used with MTX and/or LEF for the treatment of RA to reduce the side effects of the drugs and increase their efficacy.