In my work as an addiction psychiatrist, I meet people whose lives have been severely affected by alcohol or drug use, often alongside other forms of mental distress.

Some experience suicidal thoughts, some make suicide attempts, and some die by suicide. Left behind are devastated friends and family members, as well as the psychiatrists, psychologists, social workers and nurses who tried to provide treatment and support. The question that remains is often the same: why did this happen?

My research looks at patterns of health and illness across large groups of people, so it can never explain why a particular person died by suicide. But this type of research, known as epidemiology, can help us understand how common suicidal behaviour is among people with substance use disorders, and which factors are associated with greater risk.

Sweden’s national registers give us an unusual opportunity to investigate this. They contain information on diagnoses, causes of death and family relationships across millions of people.

In our latest study, we analysed data from just over 4.2 million people born in Sweden between 1958 and 1999, using records spanning 1973 to 2020. We defined “suicidal behaviour” as either a recorded suicide attempt or death by suicide.

Among the 258,046 people who had received a diagnosis of a substance use disorder, 23% had a recorded suicide attempt or death by suicide. Among people without such a diagnosis, the figure was 1.5%.

The proportion varied according to the type of substance use disorder. It was 13.6% among people diagnosed........

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