When someone has both a substance use problem and a mental health problem, it is called a co-occurring, or concurrent, disorder. Sometimes substance use can cause a mental health problem. Or, a mental health problem may lead people to use substances to relieve their symptoms. The relationship between substance use and mental health problems is more complicated than simple cause and effect. There are four types of interactions (O’Grady & Skinner, 2007):
Having either a substance use or a mental health problem greatly increases the possibility of having the other problem. Specifically, more than 15 per cent of people with substance use problems have co-occurring mental illnesses, while at least 20 per cent of people with a mental illness have a co-occurring substance use problem (CAMH, n.d.). These problems can look very similar, which makes it difficult for family members and professionals to know whether their loved one or client is experiencing a substance use problem or a mental health problem—or both.