Mohammad Reza Eskandarion ^1,2* Simin Jafaripour ³ Farid Heidari ⁴ Elham Talebi ⁵ Maryam Rezakhani Taleghani ⁶ Neda Maserat ⁷ Maryam Forutan ⁸ Raheb Ghorbani ⁹ Jaber Gharedaghi ¹ Reza Shirkoohi ² Reza Raoofian ^1*

• ¹ Legal Medicine Research Center, Legal Medicine Organization, Tehran, Iran, Tehran, Iran, Iran
• ² Cancer Research Institute, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran, Iran
• ³ Department of Biology, Irving K. Barber Faculty of Science, University of British Columbia, Okanagan Campus, Kelowna, Canada
• ⁴ Department of Psychiatry, School of Medicine, Semnan University of Medical Sciences, Semnan, Iran
• ⁵ Department of Medical Genetics, Faculty of Advanced Science and Technology, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran
• ⁶ Department of Genetics, Shahrekord University, Shahrekord, Iran
• ⁷ Department of Biology, Faculty of Science, University of Sistan and Baluchestan, Zahedan, Iran
• ⁸ Department of Biology, Islamic Azad University, East Tehran, Tehran, Iran
• ⁹ Research Center for Social Factors Affecting Health, Semnan University of Medical Sciences, Semnan, Iran

Introduction Glutathione S-transferase (GST) has the ability to detoxify the cellular environment of xenobiotic compounds and by-products of oxidative stress. The expression levels of GST genes and their polymorphisms are associated with various human diseases. Methamphetamine and opiate addiction also account for a significant proportion of SUDs in Iran. Considering the oxidative stress induced by morphine and methamphetamine and the potential of GST as a therapeutic option for SUD, we aimed to investigate the association of common genetic variations of two genes from GST family, GSTT1 and GSTM1, with addiction to morphine and METH in Iranian population. Material and Methods A total of 160 blood and urine samples were randomly collected from 50 living opiums and 30 methamphetamine users and 80 healthy controls. All samples were processed by thin layer chromatography (TLC), high performance liquid chromatography, and Gas Chromatography-Mass Spectrometry (GC-MS) techniques to detect opium alkaloids (morphine, codeine, papaverine, noscapine, etc.), methamphetamine stimulants, and other legal and illegal drugs. The genotypes of GSTM1 and GSTT1 polymorphisms were determined by PCR. Statistical analysis was performed using the SPSS. This project was approved by the Research Ethics Committee of Legal Medicine Organization, Tehran, Iran. Results A statistically significant association was observed between the GSTM1 gene and morphine addiction under a recessive genetic model. The reference group consisted of pooled n/p and p/p genotypes, with an odds ratio (OR) of 2.15, a 95% confidence interval (CI) of 1.05 to 4.39, and a P-value of 0.03. In contrast, there was no statistically significant association between genetic variations in the GSTT1 gene and morphine or methamphetamine addiction. The results revealed no significant association between GSTT1 and GSTM1 allele frequencies and morphine and methamphetamine addiction when divided into risk allele carriers and noncarriers. Conclusion These findings suggest that the GSTM1 gene may be involved in the development of morphine addiction. However, further studies with larger sample sizes are required to verify these results and investigate the underlying molecular mechanisms.