What is the impact of co-occurring mental disorders on treatment outcomes?

The influence of mental disorders on treatment outcomes in clients with AOD use disorders is not straightforward and may be influenced by a number of factors [87, 94]. Although some studies have shown that clients with co-occurring mental disorders have poorer treatment outcomes [79, 87, 91, 95, 96], others have clearly demonstrated that clients with co-occurring conditions benefit from treatment just as much as those without co-occurring conditions in terms of their AOD use, general physical and mental health, and functioning – even those with severe mental disorders [78, 87, 92, 97–102]. However, while both those with and without co-occurring conditions follow a similar course in terms of their treatment outcomes (i.e., both groups improve), those with co-occurring conditions continue to drink or use more, be in poorer physical and mental health, and display poorer functioning following treatment. That is, they present to treatment with a more severe clinical profile, and despite similar levels of improvement, continue to demonstrate a poorer clinical profile at follow-up. These findings indicate that AOD services and AOD workers do exceptionally well at treating AOD use (despite the poorer clinical profile described in the previous section) and its associated disability, but that the disability associated with the co-occurring condition remains.