Abstract: OBJECTIVE To systematically evaluate the association between OPRM1 gene A118G polymorphism and morphine dosage. METHODS Case-control study that retrieved PubMed and EMBASE databases to assess the correlation between OPRM1 gene A118G polymorphism and morphine dosage. Meta-analysis was performed by using Stata 12.0 software. RESULTS A total of 16 case-control studies involving 4 115 patients were included. The results of meta-analysis showed that the morphine requirement of wild heterozygotes(AG) of OPRM1 gene A118G polymorphism was higher than that of wild homozygotes(AA)(P=0.009), and the morphine requirement of mutant homozygotes(GG) was higher than that of homozygotes(AA)(P=0.000). The morphine requirement of dominant genetic model(AG+GG) was higher than that of wild homozygote(AA)(P=0.000). In the subgroup analysis, for race, the mutant homozygotes(GG), wild heterozygotes(AG) and wild homozygotes(AA), the requirement for morphine in the Caucasian population was higher than in the Asian population, and patient age and pain scores were also significant predictors of morphine consumption. CONCLUSION In the A118G polymorphism mutation of OPRM1 gene, G allele carriers have a higher demand for morphine, and the requirement for morphine in the Caucasian population was higher than in the Asian population.