Background People with co-occurring substance use and mental disorders have multiple and complex care needs. The combination of both disorders is very frequent and causes more adverse effects than either condition alone in terms of care needs, treatment outcomes, service access, and recovery. Therefore, it is necessary to assess their specific care needs and how these needs are met by care professionals.

Methods 562 users with co-occurring substance use and mental disorders were recruited in diverse mental health care settings in Belgium. Within a self-report questionnaire, care needs were measured using the CANSAS-P, a validated scale on met and unmet care needs. Substance use behaviour, use of services, social integration, and subjective well-being were also measured. A Latent Class Analysis was performed in order to identify users with similar profiles in terms of care needs. Then, a multinomial logistic regression was performed to identify the predictors of class-membership.

Results The highest reported unmet needs were related to intimate (40%), social (28%), and sexual relationships (27%), as well as with daily activities (31%) and physical health (29%). Three classes were identified: 1) users with few reported needs, 2) users with many reported met needs, and 3) users with many reported unmet needs. Considering the class with few reported needs as reference, poly-substance use (p = 0.039) and a low level of subjective well-being (p = 0.004) were associated with many reported met or unmet needs. In addition, being a woman (p = 0.049) and having contacts with social services (p = 0.014) were positively associated with the class with many reported met needs, while a medium level of education (p = 0.032) was negatively associated with that class.

Conclusion Interpersonal relationships are among the most reported unmet needs across all users’ profiles and should receive more attention when developing interventions. Poly-substance use is a vulnerability factor that predicts higher risk of having more (unmet) care needs. The association of other variables with care needs should be further explored. For instance, differences in terms of gender could be related to a different use of service types.