en Behavioral Neuroscience Behavioral Neuroscience Original Original <p><b>Introduction:</b> Association between single-nucleotide polymorphisms (SNPs) in mu opioid receptor gene and drug addiction has been shown in various studies. Here, we have evaluated the existence of polymorphisms in exon 3 of this gene in Iranian population and investigated the possible association between these mutations and opioid addiction. </p> <div><b>Methods:</b> 79 opioid-dependent subjects (55 males, 24 females) and 134 non-addict or control individuals (74 males, 60 females) participated in the study. Genomic DNA was extracted from volunteers’ peripheral blood and exon 3 of the mu opioid receptor gene was amplified by polymerase chain reaction (PCR) whose products were then sequenced. </div> <div><b>Results: </b>Three different heterozygote polymorphisms were observed in 3 male individuals: 759T>C and 877G>A mutations were found in 2 control volunteers and 1043G>C substitution was observed in an opioid-addicted subject. Association between genotype and opioid addiction for each mutation was not statistically significant. </div> <div><b>Discussion:</b> It seems that the sample size used in our study is not enough to confirm or reject any association between 759T>C, 877G>A and 1043G>C substitutions in exon 3 of the mu opioid receptor gene and opioid addiction susceptibility in Iranian population.</div> Addiction, OPRM1 Gene, Polymorphism. 18 21 http://bcn.iums.ac.ir/browse.php?a_code=A-10-1-190&slc_lang=en&sid=1 Amin Dinarvand 1370031947532846006415 1370031947532846006415 No Science and Research Branch of Islamic Azad University, Tehran, Iran. Ali Goodarzi 1370031947532846006416 1370031947532846006416 No Iranian National Center for Addiction Studies, Tehran University of Medical Sciences, Tehran, Iran. Nasim Vousooghi 1370031947532846006417 1370031947532846006417 No Department of Neuroscience, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mehrdad Hashemi 1370031947532846006418 1370031947532846006418 No Department of Genetics, Islamic Azad University, Tehran Medical Branch, Tehran, Iran Rasoul Dinarvand 1370031947532846006419 1370031947532846006419 No Department of Pharmacoeconomics and Pharmaceutical Administration, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. Fahimeh Ostadzadeh 1370031947532846006420 1370031947532846006420 No Science and Research Branch of Islamic Azad University, Tehran, Iran. Ahad Khoshzaban 1370031947532846006421 1370031947532846006421 No Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran. Mohammad-Reza Zarrindast 1370031947532846006422 1370031947532846006422 Yes Iranian National Center for Addiction Studies, Tehran University of Medical Sciences, Tehran, Iran.