Background. The combined use of intramuscular injection glycosaminoglycan peptide complex (GPC) and oral diacerein can increase the effectiveness of treatment of osteoarthritis (OA). Aim. Compare the effectiveness of combination GPC + diacerein and GPC monotherapy in the treatment of OA in clinical practice. Materials and methods. A retrospective evaluation of the results of a 12-week multicenter observational non-interventional study of the effectiveness of GPC (Rumalon, a course of intramuscular injections 3 times a week, №25) in patients with moderate/severe OA (n=2955) requiring regular administration of nonsteroidal anti-inflammatory drugs (NSAIDs). The analysis identified a group of patients (n=414) who received GPC in combination with diacerein 100 mg/day (Diaflex Rompharm). The therapeutic effect was compared in the groups of GPC monotherapy (n=2541) and the combination of GPC with diacerein. These groups did not differ in average age (61.411.8 and 61.911.3 years), both were dominated by women (76.3 and 70.3%), there was approximately equal intensity of pain during movement and impaired joint function: 6.11.8/6.01.6 and 4.92.1/5.11.8 (according to the numerical rating scale 010). The dynamics of pain intensity, the need for NSAIDs, and the frequency of adverse events (AE) were compared 12 weeks after the start of treatment. Results and discussion. In the majority of patients with OA both on the background of GPC monotherapy and combined use of GPC and diacerein, there was a significant improvement. The number of patients with pain reduction 50% was 54.3 and 62.8% (p0.001), NSAID administration was completely stopped in 66.7 and 77.5% (p0.001), respectively. The effectiveness of the combination of GPC and diacerein was significantly higher than that of GPC monotherapy in OA of the knee joint, hip joint, and generalized OA. AE from the gastrointestinal tract was observed in 7.8 and 8.9%, arterial hypertension in 6.3 and 4.6%, allergic reactions in 0.3 and 0.5% of patients (not significant). Conclusion. The application of the code of civil procedure is an effective treatment for OA. The combination of GPC and diacerein provides a more significant improvement than GPC monotherapy. GPC and diacerein (including in combination) are well tolerated and rarely cause AE.