Statistical analyses were conducted using SPSS for Windows (Version 19.0). The counting data, such as methylation and non-methylation values, were compared using t-tests, and the measurement data were compared using chi-square tests. The Pearson method was used to analyze the correlation between CHN2 methylation levels and other factors, including the age of starting taking MA, the total duration of MA use, and combination with other psychoactive substances.
