The effects of opium consumption on glycemic indices: a systematic review and meta-analysis of human and animal studies.

BACKGROUND: Glucose metabolism disorders, such as insulin resistance and diabetes, are major public health challenges influenced by lifestyle factors and substance abuse, including opium. This study aims to clarify the ambiguous effects of opium on glycemic indices through a systematic review and meta-analysis of human and animal studies. METHODS: A comprehensive search was conducted in PubMed, Scopus, and Web of Science up to June 2025. Article screening was independently performed by three reviewers in two stages. Data extraction and quality assessment were carried out by independent researchers using the Joanna Briggs Institute scale, and statistical analyses were performed using Stata14. RESULTS: This meta-analysis included 22 studies (12 human and 10 animal studies, analyzed separately). The human studies, 84% of which were conducted in Iran, analyzed a total of 6,106 participants (2,312 opium users and 4,794 controls). The results of the meta-analysis generally showed that opium was able to partially, but statistically significant reduction in FBS (SMD = -0.14; 95% CI: -0.28 to -0.01; I² = 58.7%; p = 0.05) and a non-significant reduction in HbA1C (SMD = -0.21; 95% CI: -0.45 to 0.03; I² = 62.7%; p = 0.02). Animal studies consistently demonstrated elevated blood glucose levels following morphine administration. CONCLUSIONS: This meta-analysis suggests that opium consumption may slightly reduce FBS levels, but has no consistent effect on HbA1C, indicating a likely transient impact on glycemic control.The geographical concentration of human studies in Iran is a major limitation, and cohort and prospective studies in diverse populations are needed to clarify the underlying mechanisms and long-term effects of opium on glycemic indices.