BACKGROUND: Mental health clinicians are uniquely suited to support and provide important insights about substance use among pregnant patients. This mixed-methods study explored how mental health clinicians perceive and address prenatal cannabis use. METHODS: Participants were licensed mental health clinicians from Kaiser Permanente Northern California's Early Start perinatal substance use screening and counseling program. Participants aimed to support patients' goals for a healthy pregnancy. ESS completed a survey ( RESULTS: Survey results indicated clinicians perceive that nausea/morning sickness was the most common motive for prenatal cannabis use, and pregnant individuals were most likely to get information about prenatal cannabis use from their peers. Survey and interview results indicated clinicians most often used motivational interviewing, harm reduction, and psychoeducation to address cannabis use. Clinicians reported on psychotherapeutic factors (patient readiness, therapeutic rapport, and mental health support) that facilitate engagement and willingness to quit and/or reduce cannabis use during pregnancy. Other themes included ESS utilization of expertise in complementary mental health topics to support their work. CONCLUSIONS: In this mixed-methods study, clinicians described several approaches to increase pregnant patients' willingness to engage in perinatal substance use interventions, including eliciting motives for cannabis use and using patient-centered interventions focused on establishing rapport and addressing readiness to quit. Future interventions for patients might incorporate harm reduction and psychoeducation, address motivations for use and readiness to engage in care, emphasize peer support, and support the implementation of complementary interventions.