Multidimensional family therapy decreases the rate of externalising behavioural disorder symptoms in cannabis abusing adolescents: outcomes of the INCANT trial

Background: US-based trials have shown that Multidimensional Family Therapy (MDFT) not only reduces substance abuse among adolescents, but also decreases mental and behavioural disorder symptoms, most notably externalising symptoms. In the INCANT trial, MDFT decreased the rate of cannabis dependence among Western European youth. We now focus on other INCANT outcomes, i.e., lessening of co-morbidity symptoms and improvement of family functioning. Methods: INCANT was a randomised controlled trial comparing MDFT with individual therapy (IP) at and across sites in Berlin, Brussels, Geneva, The Hague, and Paris. We recruited 450 boys and girls aged 13 up to 18 years with a cannabis use disorder, and their parent(s), and followed them for 12 months. Mental and behavioural characteristics (classified as 'externalising' or 'internalising') and family conflict and cohesion were assessed. Results: From intake through 12 months, MDFT and IP groups improved on all outcome measures. Models including treatment, site, and referral source showed that MDFT outperformed IP in reducing externalising symptoms. Adolescents were either self-referred to treatment (mostly on the initiative from people close to the teen) or referred under some measure of coercion by an external authority. These two groups reacted equally well to treatment. Conclusions: Both MDFT and IP reduced the rate of externalising and internalising symptoms and improved family functioning among adolescents with a cannabis use disorder. MDFT outperformed IP in decreasing the rate of externalising symptoms. Contrary to common beliefs among therapists in parts of Western Europe, the 'coerced' adolescents did at least as well in treatment as the self-referred adolescents. MDFT shows promise as a treatment for both substance use disorders and externalising symptoms