addictions, individual differences in the apparent effectiveness of these drug treatments has led to increasing interest in pharmacogenetics, the study of genetic variation underlying individual differences in both drug metabolism and response to the effects of drugs.165 Despite some non-replications, three independent studies have reported that carriers of the A118G polymorphism (rs1799971) in OPRM1 respond more positively to naltrexone treatment for alcohol dependence.166, 167, 168 Another promising treatment for alcoholism, ondansetron, a 5-HT3 (5-hydroxytryptamine (serotonergic) receptor 3) antagonist has been found to be a particularly useful treatment in early-onset (Type II) alcoholics, while the selective serotonin reuptake inhibitor (SSRI) sertraline has been found to be more efficacious in later-onset (Type I) alcoholics.169, 170
