The naltrexone-treated group had significantly more heroin-free urine samples at the 10-week assessment, and the difference in amphetamine-free samples approached significance. Fifty-two percent of the urine samples were heroin free versus 20% in the placebo-treated group, and 40% of the samples were amphetamine free versus 24% in the placebo-treated group. Among the patients who continued to use amphetamines, the naltrexone-treated group had fewer instances of use, although again the difference just missed statistical significance. When urine samples were analyzed for the presence of either drug, 38% of the naltrexone-treated group were found to be drug free, compared with only 16% of the placebo-treated group (Figure 1, left). Two clinical assessments of illness severity and treatment outcome showed that the naltrexone-treated patients had substantially more and significantly greater improvement. On the CGI, 56% showed much or very much improvement, compared with only 14% of the placebo patients, and the mean GAF scores were 82.0 for the naltrexone-treated patients and 71.9 in the placebo-treated arm. Retention in the study for 10 weeks was significantly better for the naltrexone-treated group: 52% versus 28% for the placebo implant group (Figure 1, right side). There was not a significant medication effect on craving, with both groups overall showing decreases. Of interest, however, is that patients in the naltrexone-treated group who continued to use amphetamine reported significantly less of an amphetamine effect, indicating that naltrexone suppressed the euphoric effect more than placebo. Minor changes in liver enzymes were noted, but no difference between groups in adverse reactions were observed during the course of the study.