Researchers for the first time treated alcohol-dependent individuals with medication that is designed specifically to match their genetic profile. The individuals were tested with ondansetron, a serotonin antagonist drug. These findings suggest a new paradigm for the treatment of alcoholism, as well as a major breakthrough in individualized medicine for predetermined genotypes. The study tested 283 genetically profiled alcoholics for the efficacy of ondansetron, a serotonin antagonist drug. Serotonin is a brain chemical that is involved in the regulation of pain perception, sleep, mood and other psychological processes. Studies have shown that serotonin mediates the rewarding effects of alcohol. Researchers randomised alcoholics by genotype in a controlled, double-blind clinical trial. Subjects received either ondansetron or placebo for 11 weeks, and all received standard cognitive behavioral therapy. For subjects with the LL/TT genotype, those treated with ondansetron, on average, fell below the high-risk drinking category, while those who received placebo remained in the high-risk category. In addition, these same genotype categories responded more positively to ondansetron, versus placebo, in increasing the days of abstinence. The finding appeared online and will be published in the March issue of the American Journal of Psychiatry.