My name is Dr. Kwame MacKenzie
I am a psychiatrist at the Centre for Addiction and Mental Health and the University of Toronto. I am here today to talk about the cause of psychosis.
So when people think of the cause of an illness, they always think of something like pneumonia, where you get a bug and that bug causes the illness. But that is not how most illnesses are caused. Most illnesses you don't find one
single thing that causes the illness. It is more like heart disease. We all know that you might be at risk of heart disease because of your family, but we also know that whether you get a heart attack or not depends on the
things that happen to you: how much stress you have in your life, how much exercise you do, whether you smoke, what your diet is like. All of those things are important for your risk of heart disease. Not a simple cause, your
risk of heart disease. And of course, what you eat, how much you exercise and what sort of job you have, depending on where you are. So your risk of heart disease is partly due to who you are—your genes—but a lot do with what
happens to you as you go along in life. It is not a simple cause. It is things that happen to you that increase your risk.
Schizophrenia is exactly the same as heart disease. You don't find a single cause for schizophrenia, but there are lots of things that increase your risk. When people are thinking of those things that will increase your risk, they
really put them into two big buckets, biological and social.
When people are thinking about biological, they are thinking about physical things, like your genes or like taking cannabis, that increase your chance of developing a psychosis. Now, we all know that if somebody in your family
has been diagnosed with schizophrenia or any psychosis, you are more likely to develop it yourself. But the truth is, most people who develop psychosis don't have any clear family of history of psychosis at all. We also all
know that some things, like taking cannabis, increase your risk of developing psychosis. There are other things that most people maybe don't know about. If you have had a difficult birth, so an obstetric complication, that
also increases your risk of developing a psychosis later in life. There are these biological factors that people talk about. And obstetric complications, cannabis and heredity or genes are the things that people generally think
are important. There are lots and lots and lots of other risks but those are the ones that people talk about.
Then there are social factors. Social factors have had a lot of research recently and they have shown us some interesting things. For instance, if you life in a city when you're young, you have an increased chance of developing
psychosis. If you are separated from your parents before the age of 15, again, you have an increased risk of psychosis. If you are bullied, or you have social adversity when you are young, you have an increased risk of developing
psychosis. And those sorts of social adversities can also increase your risk of psychosis: if you are older, if you are a victim of racism when you are older, if you are unemployed. All of those things that lead to social stress
increase your chance of developing a psychosis. The list is very long of the social factors that can increase your risk of psychosis.
Where the confusion happens is we often see the thing that happens, say for instance, taking cannabis when somebody is 16 or 17 we say, well that was the cause. What we don't see is the vulnerability is generated earlier. It is
never, almost never, one cause. It is loads of little risk factors that are working together to increase your risk of developing a psychosis.