Int. J. Environ. Res. Public Health 2009, 6 3065 for methamphetamine use. For Japanese inmates, methamphetamine abuse may have some association with problematic alcohol drinking. The inmates tended to have a better employment status than patients. Most of the inmates had regular jobs, received wages, and did not receive financial support. That is, they lived a relatively financially independent life compared with patients, although many of them received a substantial amount of money illegally. Additionally, the inmates tended not to experience psychotic symptoms, such as hallucinations, and not to access medical services for their addictive problems. Many patients received treatment for the distress associated with psychotic symptoms rather than for the drug abuse itself [23]. These results indicate that inmates abused drugs within a range before their arrest, but their psychiatric symptoms were apparently not as severe as those among patients. Problems appeared to exist in the inmates’ environments while they were young. Many of them had less education and a history of juvenile delinquency. These results are consistent with the results of Miura et al. [7] in which the number of admissions to a juvenile detention home significantly predicted methamphetamine use during adolescence. Moreover, a history of inhalant abuse was found in more than half of the inmates. Inhalant abuse, such as paint thinner abuse, was found to be a significant problem leading to methamphetamine abuse among young Japanese [2]. Our results, combined with these previous results, suggest that a troubled childhood may lead to illegal drug use in adulthood. Methamphetamine-induced psychosis is reported frequently in Japanese patients diagnosed with methamphetamine dependence [6]. Additionally, Wada and Fukui [24] reported that five years of methamphetamine use is considered a turning point in terms of the occurrence of psychotic symptoms, suggesting that a shorter duration of methamphetamine abuse in inmates may be related to less frequent psychosis. However, no significant association was found between the duration of methamphetamine abuse and lifetime experience of psychosis in the inmates and patients in the present study. Interestingly, inmates reported fewer psychotic symptoms, such as hallucinations, than patients, although no significant differences were found in age between the two groups. This result may reflect the fact that inmates with acute psychosis were excluded from the study. Nonetheless, the present results suggest that inmates and patients may have different backgrounds contributing to vulnerability to methamphetamine-induced psychosis. Further studies with more inmate and patient samples using multivariate statistical analysis will be needed to reveal the factors leading to vulnerability to methamphetamine-induced psychosis in methamphetamine dependence/abuse. With regard to route of methamphetamine administration, intravenous injection was used by most of the inmates, whereas a minority of patients used this route. These results are consistent with the results of Matsumoto et al. [6] in which methamphetamine-injecting subjects had more extensive criminal records than smoking subjects. Matsumoto et al. investigated outpatients and reported significant differences in life circumstances between injecting and smoking abusers, and injecting abusers appeared to have greater antisocial tendencies than smoking abusers. Moreover, Matsumoto et al. reported that although methamphetamine abusers often claimed that smoking is safer than injection, no significant differences were found in the overall occurrence of psychotic symptoms between injection and smoking. Our results consistently showed that the injection route, which was used by most of the inmates, might not be a factor causing critical psychotic problems.