Public health risks associated with methadone in Iran: A systematic review and meta-analysis

Background: There has been a marked growth in methadone maintenance treatment (MMT) in Iran in the past two decades with positive health outcomes. We conducted a systematic review of studies on the prevalence of non-prescribed methadone use, methadone use disorder, and methadone-related poisoning and mortality in Iran. Methods: We searched International and Iranian databases up to May 2020 and contacted relevant experts. The pooled proportions were estimated through random-effects model. Methadone-related adverse outcomes were evaluated over time. Results: Sixty-five studies were included. The pooled estimates of non-prescribed methadone use in the last 12-month were 2.7% (95%CI: 0.9–5.4) and 0.1% (95%CI: 0.03–0.2) in the male and female general population, respectively. Among people who use drugs, 8.4% reported daily non-prescribed use in 2018. Four heterogeneous studies in drug treatment centers reported the existence of treatment-seeking for methadone use disorder. Methadone was responsible for 10.4% (95%CI: 4.5–18.3) of cases of acute poisoning in adults and 16.0% (95%CI: 9.3–24.1) in children. Methadone was reported as a cause of death in 53.5% of substance-related deaths referred to the Legal Medicine Organization while being the only cause in 35.8% of all cases. Conclusion: Non-prescribed use of methadone in the general population is much less than opiates and some other available prescription opioids, like tramadol. However, notwithstanding the large and successful MMT program in Iran, increasing trends in methadone-related poisoning and deaths pose serious public health concerns. There is an urgent need to explore these fatal and non-fatal poisoning cases and implement policies to curb the harms associated with methadone use.