It can be argued that an individual’s subjective experience and beliefsabout a substance are important. Motives and expectancies regarding the use ofalcohol and drugs are often that they are going to modify a cognitive state orhelp them cope with a particular situation. However, there are growing concernsin the U.S.A. and in the U.K. regarding individuals who experience psychosis andconcurrently use substances. Correctly diagnosing individuals with dualpresentation is said to be difficult, engagement in treatment is problematic, andmedication adherence and prognosis poor. In this paper a cognitive-developmentalmodel is proposed. I suggest that for individuals who experience psychosis andalso use drugs or alcohol, the ability to identify the relationship between thesubstance use and the psychotic illness in terms of a case formulation/conceptualizationwould provide a good starting point for developing strategies and interventionsthat are most likely to succeed in treatment. Such an approach would explicitlyaddress key cognitions. Unless the dysfunctional substance-related beliefs areaddressed, adherence to medication and engagement with treatment services willbe hindered and the possibility of relapsing to problematic substance use andacute psychosis remains. A cognitive treatment component, to target these beliefs,based on the cognitive model of substance misuse and the motivationalinterviewing approach will also be briefly outlined.