Impact of opium on bladder cancer incidence: A systematic review and meta-analysis

Introduction: Opium is used recreationally and for pain relief in certain regions and has been classified as a human carcinogen by the IARC. While its use is rare in Europe and Oceania, it remains a major public health issue in other parts of the world. This study evaluates the risk of bladder cancer (BCa) among opium users compared to non-users. Methods: A comprehensive search of MEDLINE, Scopus, and Web of Science was conducted up to July 2024 to identify studies examining the link between opium use and BCa. A meta-analysis was performed to calculate the pooled risk ratio (RR) with 95% confidence intervals (CIs) (PROSPERO: CRD42024562623). Results: A total of 15 studies (n=60,149) were included. The analysis showed that opium users had a significantly higher risk of developing BCa than non-users (RR: 2.36; 95% CI: 1.92-2.90; P<.001). The risk increased with the amount of opium consumed, regardless of type or method of use. Conclusions: Opium consumption increase the risk of developing BCa by more than twofold among users. Awareness of its carcinogenic potential and public health implications is crucial. Our findings underscore the need for global prevention strategies and further research into opium-related BCa risks.