Abstract The impact of social factors on individual and population mental health are well established (Kirkbride, et al., 2024). The same social factors may trigger the substance use behavior developing into substance use disorders. Mental health disorders can contribute to the substance use and substance use disorders with worsening effects over time (EMCDDA, 2016). This association between substance use, substance use disorders and mental health disorders is a key objective for the scientific consideration and policy development. Respective phenomena are universal and a broader perspective would be useful for a better understanding of how the issue of comorbidities of substance use and mental disorders are addressed on a European level. Identification of the substance use problem, especially among populations in vulnerable situations, like migrants, becomes utterly important. Heterogenous systematic reviews show that there is a need for socially and culturally refugee sensitive instruments to measure the substance use in migrants. Oftentimes substance use is followed by the substance use disorders and drug use related infections. Injecting drug use is also a risk factor for having drug use related infections, such as hepatitis B and C, HIV, tuberculosis. Assessment of risk behaviour patterns among people who inject drugs may contribute to a higher participation in treatment and health programmes, reduce the burden of substance use and tackle comorbidities of substance use and mental health disorders. The skill building seminar aims to increase the knowledge and capacities on substance use and comorbidities, applied methodological approaches and tools in different European contexts. This workshop will support researchers, policy makers, public health planners by providing evidence base to address substance use and mental health issues. The added value of this workshop is based on the structure, content and mode of presentations - presentations will be followed by questions from participants and short discussions. The workshop will start with the general introduction to the topic of comorbidities of substance use and mental health disorders (EUPHA-PMH and EUDA). Then the European level perspective on comorbidities of substance use and mental health disorders will be presented including recent policy developments (1 presentation by Linda Montanari, EUDA). It will be supported with research results from the study conducted in Germany on substance use assessment tool development in migrant population (2 presentation by Kim-Julian Behr, Germany) and behavioural risk factor assessment study among people who inject drugs in Lithuania (3 presentation by Marija Jakubauskiene, Lithuania). Key messages • Participatory approach is useful to address the substance use problem in assessment tool development and further monitoring. • Better understanding of comorbidity of substance use and mental disorders leads to a more effective prevention.