Observational studies: In a study involving 1268 RA and T2DM patients, Lu et al. observed that administering Metformin with cyclooxygenase-2 (COX-2) inhibitors lowered admission rates compared to COX-2 inhibitors alone.35 In an 18-year cohort study involving 113,749 adult metformin users, Naffaa et al. found that treatment adherence was associated with decreased RA risk. Here, PTGS2 is linked to rheumatoid arthritis.