Associations between methamphetamine use, psychiatric comorbidities and treatment outcome in two inpatient rehabilitation centers

•The number of substance related diagnoses at admission predicts treatment dropout.•Non substance related psychiatric diagnoses do not predict treatment dropout.•62% of the treatment seeking methamphetamine users were diagnosed with F12.2.•Depressive disorders were the most frequent comorbidities at beginning of treatment.•Diagnoses vary over treatment process. The use of methamphetamine is spreading globally and provokes the need for effective treatment options. Previous research showed increased psychiatric comorbidities in methamphetamine users, but its impact on treatment success is still unclear. This study investigates data from two German addiction rehabilitation centers including 108 methamphetamine using individuals. The participants were tested and interviewed at the beginning of the addiction treatment program and at the end of treatment after about six months. In total, 95% of the participants had at least another psychiatric diagnosis. At admission, substance related comorbid diagnoses (meaning abuse or addiction of other substances than methamphetamine) showed a significant effect on treatment dropout. Within the substance related diagnoses, the majority of participants (62%) suffered from cannabinoid dependency. Non-substance related comorbidities and the total number of comorbid diagnoses did not have an impact on treatment outcome. The most frequent non substance specific diagnosis at admission was a depressive disorder (15%). Diagnoses patients had at discharge did not show any effects on the treatment completion. Comparing diagnoses at admission and discharge revealed slight differences, which may rise from a better assessment at discharge due to the fact that clinicians got to know the patients better during the therapeutic process.