Previous studies reported that clinical presentations of patients with substance use disorder (SUD) have different forms depending on the substance of abuse; however, the difference in treatment prognosis due to the substance of abuse has not been clarified. The aim of this study was to compare the duration of abstinence of patients with SUD by substance of abuse and to examine associated factors using a 3-year prognosis survey after their first visit to an addiction clinic.
 Subjects: SUD patients who first visited the Kanagawa Psychiatric Center Addiction Clinic (Japan) between May 2015 and April 2018 were asked to complete a series of self-administered questionnaires including 17 items concerning adverse childhood experiences (ACEs), the Sense of Trust Scale, Sense of Rejection Scale, Sense of Coherence Scale, and screening for addiction severity. Three years after the first visit, they were asked to respond to a prognostic survey to investigate their longest period of abstinence and their living conditions during the three years. A total of 711 patients responded to self-administered questionnaires, and of them, 397 patients responded to the prognostic survey. Respondents of the prognostic survey were divided into three groups according to the common substances of abuse: group 1 (alcohol, n=223), group 2 (illicit drugs, n=129), and group 3 (prescription and over-the-counter medications, n=45). We plotted Kaplan-Meier curves, and conducted log-rank tests to examine and compare abstinence periods for each group. To investigate the factors associated with relapse to alcohol or drug abuse, we performed a Cox proportional hazard regression model.
 Results: Estimated median abstinence period during the three years of groups 1,2, and 3 was 6 months (95% confidence interval: 3.83-8.17), 32 months (95% confidence interval could not be estimated due to relapses), 12 months (95% confidence interval: 9.39-14.61), respectively. The duration of the abstinence period of group 1 was significantly shorter than that of group 2 (p<.01), and group 3 was also significantly shorter than group 2 (p<.01). There was no significant difference between group 1 and group 3. Multivariate analysis by Cox proportional hazard model confirmed that in group 1, a history of addiction treatment, continued outpatient treatment, and continued participation in self-help groups were inhibiting factors of relapse, and suicidal behavior in the last three years was a risk factor for relapse. In group 2, male patient, past history of chronic physical disorder, childhood bullying, childhood neglect, and loss of financial independence in the last three years were risk factors for relapse. In group 3, childhood separation from one or both of parents, chronic physical disorder in their family during childhood, high scores of distrust in the Sense of Trust Scale at first visit of addiction clinic, and history of suicidal behavior in the last three years were risk factors.
 Conclusion: The alcohol group and the prescription and over-the-counter medications group, for which the substance of abuse is relatively easy to obtain, had a different duration of abstinence from the illegal drug group. Therapeutic tasks should be tailored to each group according to the difference in clinical pictures and prognostic factors. It is necessary to alleviate the distrust that comes from childhood adversity experiences and build therapeutic alliances for better treatment retention. Motivating patients to participate in self-help groups, providing support for economic independence, and responding empathically to suicidal ideation are also essential in preventing relapse of SUD patients.
 Authors' abstract