Abstract: Twenty-three trials (total of 912 patients) met the inclusion criteria (22 in RA; one in a mixed population of RA and osteoarthritis); all except one were published before 1990. Most study populations were not taking DMARDs (e.g. methotrexate, sulphasalazine, hydroxychloroquine and leflunomide) and all studies were performed prior to the introduction of biologic therapies (e.g. etanercept, infliximab and adalimumab). All trials were at high risk of bias, heterogeneity precluded meta-analysis, and we were only able to report a general description of results. The majority (18 studies, 78%) found no differences between the combination and monotherapy treatments they studied, while five (22%) reported conflicting results, favouring either the combination or monotherapy arms. From the 12 trials on NSAID + analgesic vs NSAID, nine reported no significant difference between the interventions, while three did: in two, the combination therapy achieved better pain control; and the third trial compared combination therapy with two different dosages of monotherapy (NSAID alone) and reported that a high dose phenylbutazone was superior to combination therapy (paracetamol + aspirin), which was superior to low dose phenylbutazone. From the five studies on the combination of two NSAIDS vs one NSAID, four reported no significant differences between interventions, and one reported significantly better pain control with combination therapy. The single trial comparing a combination of opioid + neuromodulator vs opioid reported better pain control with monotherapy. The remaining trials (NSAID + neuromodulator vs NSAID (3 trials); opioid + NSAID vs NSAID (1 trial); and opioid + analgesic vs analgesic (1 trial)) found no significant difference between combination therapy and monotherapy. Information regarding withdrawals due to inadequate analgesia and safety was incompletely reported, but in general there were no differences between combination therapy and monotherapy. No data were available that addressed the value of combination pain therapy or monotherapy for people with IA who have optimal disease suppression. There were no studies that included patients with AS, PsA or SpA. Based on 23 trials, all at high risk of bias, there is insufficient evidence to establish the value of combination therapy over monotherapy for people with IA. Importantly, there are no studies addressing the value of combination therapy for patients with IA who have persistent pain despite optimal disease suppression. Well designed trials are needed to address this question.

Plain-language summary: There is insufficient evidence to establish the value of combination therapy over monotherapy for people with IA. We included 23 studies in this review, all at high risk of bias (i.e. high chance of giving invalid results). Twenty-two of the trials were in patients with RA and one in a mixed population (RA and osteoarthritis). There were no studies in patients with AS, PsA or SpA. Included studies were old (all but one were published before 1990) and patients were, in general, not on optimal disease-modifying antirheumatic drugs, as is standard current practice. Therefore, it is not possible to draw conclusions about the value of combination pain therapy over monotherapy for people with IA. Importantly, there are no studies addressing the value of combination therapy for patients with IA who have persistent pain despite optimal disease suppression. Well designed studies are needed to address this question.