Background Biologic (b) and targeted synthetic (ts) disease-modifying anti-rheumatic drugs (DMARDs) used in the management of rheumatoid arthritis (RA) target inflammatory pathways implicated in the pathogenesis of multiple myeloma (MM). It is unknown whether use of b/tsDMARDs affects the incidence of MM. Methods In this cohort study using Veterans Health Administration (VHA) data, we identified Veterans newly diagnosed with RA from 1/1/2002 to 12/31/2018 using diagnostic codes and medication fills. DMARD exposure was categorized as follows: conventional synthetic (cs)DMARDs; bDMARDs, which included tumor necrosis factor inhibitors (TNFi), non-TNFi; and a tsDMARD, tofacitinib. A Cox proportional hazards model with time-varying exposure was used to estimate the hazard ratio for developing MM among those who received b/tsDMARD medications relative to b/tsDMARD-naïve persons. Results 27,540 veterans with RA met eligibility criteria of whom 8322 (30%) took a b/tsDMARD during follow-up. The