People with substance use disorder are at a significantly higher risk of both attempted suicide and death by suicide. This is shown by a study from the Karolinska Institutet published in the journal Molecular Psychiatry. The study also shows that the risk of suicidal behaviour is elevated among relatives of people with substance use disorder, particularly among close relatives.

In the study, the researchers analysed data from Swedish national registers covering just over 4.2 million people born in Sweden between 1958 and 1999. The participants were followed from 1973 to 2020. The researchers investigated the link between substance use disorders – that is, problematic use of alcohol or drugs – and suicidal behaviour, defined as suicide attempts or death by suicide.

Of the approximately 258,000 people who had been diagnosed with a substance use disorder, 23 per cent had at some point attempted suicide or died by suicide. The corresponding proportion among people without such a diagnosis was 1.5 per cent. The highest prevalence was seen among people with both alcohol and drug dependence, where 44 per cent had experienced a suicidal event.

After the researchers had taken into account factors such as gender, year of birth, socio-economic circumstances and other psychiatric diagnoses, a clearly elevated risk remained. People with substance use disorder had more than six times the risk of suicidal behaviour compared with those without the diagnosis. The risk was highest for those with both alcohol and drug dependence.

The researchers also investigated whether the risk runs in families. The analysis showed that people whose relatives had substance use disorders were more likely to have experienced a suicidal event themselves. The association was stronger between close relatives than between more distant relatives, suggesting that genetic factors may play a role. Shared environmental factors within the family may also be significant.

“Our findings suggest that a family history of substance use disorder is not only a risk factor for one’s own addiction problems but may also be a marker of an increased risk of suicidal behaviour,” says lead author Lotfi Khemiri, a specialist in psychiatry and researcher at Department of Medical Epidemiology and Biostatistics, Karolinska Institutet and Department of Clinical Neuroscience, Karolinska Institutet.

The researchers emphasise that the findings may be important for clinical practice. According to the study, healthcare professionals should be aware of the increased risk of suicide among people with substance use disorders, particularly those who also have alcohol and drug dependence or other psychiatric diagnoses.

“The study also highlights the need for further research into interventions that can prevent suicide among people with substance use disorders. Just as with other psychiatric conditions, it is important that staff who come into contact with people with substance use disorders are aware of the increased risk of suicide and know how to assess it,” says Lotfi Khemiri.

The researchers emphasise that the study is based on diagnoses recorded within specialist healthcare and therefore primarily reflects the more severe forms of substance use disorders. As the study is based on Swedish register data, it is also unclear to what extent the results can be generalised to other countries.

See the study for details of funding and any conflicts of interest.