Why do co-occurring conditions occur?

There are a number of possible explanations as to why co-occurring conditions may occur (see Figure 2):

• The presence of a mental health condition may lead to an AOD use disorder, or vice versa (known as the direct causal hypothesis).
• There may be an indirect causal relationship.
• There may be factors that are common to both the AOD and mental health condition, increasing the likelihood they will co-occur.