Substance-use disorders linked to sixfold higher risk of suicidal behaviour – new study

A study of 4.2 million people found a strong link between substance-use disorders and suicidal behaviour, with family patterns offering further clues.

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Support from family members and healthcare professionals can be important for people with substance-use disorders who may also be at increased risk of suicidal behaviour. Pormezz/ShutterstockIn 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 with alcohol use disorder, and 26% among those with drug use disorder. Among people diagnosed with both alcohol and drug use disorders, it rose to 44.4%.

These figures need some context. The Swedish registers mainly captured substance-use disorder diagnoses made in hospitals and specialist outpatient services, and did not include diagnoses recorded only in primary care. Those identified in our study may therefore have had more severe substance-use problems than many people in the wider population.

So, the 23% figure should not be interpreted as meaning that nearly one in four people with a substance use disorder will attempt or die by suicide.

Other mental health conditions were also important. Depression, anxiety disorders, bipolar disorder and ADHD were more common among people with substance use disorders who had experienced suicidal behaviour.

Even after we statistically accounted for factors including sex, birth year, socioeconomic circumstances and co-occurring psychiatric conditions, people with a substance-use disorder had more than six times the risk of a recorded suicide attempt or death by suicide, compared with people without one.

Relatives with a substance-use disorder

Our study looked at whether substance-use disorders and suicidal behaviour had both been recorded during a person’s lifetime, rather than establishing which came first. It therefore cannot tell us that the substance use disorder caused a suicide attempt or death.

Previous Swedish research has, though, found a substantially increased risk of death by suicide across different substance use disorders.

Because the Swedish registers contain information about family relationships, we could also investigate another question: is having a relative with a substance-use disorder associated with a person’s risk of suicidal behaviour?

We compared people whose cousins, half-siblings, full siblings or twins had a substance use disorder. The more closely related people were genetically, the stronger the association tended to be. For example, the risk was greater when a full sibling had a substance-use disorder than when a half-sibling or cousin did.

This pattern suggests that some of the factors that make people vulnerable to substance-use disorders may also increase vulnerability to suicidal behaviour. Genetic influences appear to contribute to this overlap, alongside environmental and individual factors. This fits with previous research using Swedish family and twin data that has also found shared genetic influences between substance-use disorders and suicidal behaviour.

Genes influence risk rather than determining somebody’s future. Family circumstances, individual experiences and many other factors can also affect whether somebody develops a substance-use disorder or experiences a suicidal crisis.

Practical implications

For clinicians, the findings have practical implications. A family history of substance-use disorder, particularly in a close relative, may provide useful additional information when assessing someone’s mental health and suicide risk.

People with both alcohol and drug-use disorders may require particular attention, because this group had the highest proportion of suicidal behaviour in our study.

The findings also highlight a gap in treatment research. Evidence for treatments specifically designed to reduce suicidal behaviour in people with substance-use disorders remains limited.

A 2020 review of randomised controlled trials found only six studies, and concluded there was not enough evidence to establish whether these interventions prevent suicide or reduce self-harm. More recent research has also found that suicidal behaviour is rarely assessed consistently among people undergoing treatment for substance-use disorders.

Suicide prevention therefore needs to be integrated into addiction care. I believe that clinicians should ask about suicidal thoughts and previous attempts, recognise other mental health conditions that may increase risk, and ensure people can access appropriate psychiatric support.

For families, I hope these findings provide some context without creating a sense that outcomes are inevitable.

Substance-use disorders and suicidal behaviour appear to share some underlying vulnerabilities, including genetic influences. Understanding this overlap may help people recognise risk earlier, discuss relevant family history with healthcare professionals, and seek help when concerns arise.

No population study can explain an individual death. What research across millions of people can do is identify groups in whom the risk is particularly high. This should give healthcare services better information about where prevention efforts are most urgently needed.
Lotfi Khemiri receives funding from Region Stockholm, the Swedish Mental Health Fund (Fonden för Psykisk Hälsa), and the Centre for Psychiatry Research at Karolinska Institutet.

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