Time in host country - a risk factor for substance abuse in migrants

Millions of people die each year from the consequences of alcohol and drug abuse and treatment of these addictions causes massive strains on public health systems. With more than 258 million people currently living as migrants outside their birth country, the researchers in this study wanted to examine the prevalence of substance use disorders in different migrant groups relative to the local population in their host country, and whether addiction rates changed over time.

The researchers used Sweden’s unique linked registers to gather information on more than 1.2 million people aged up to 32 years old, including more than 17,000 refugees and more than 100,000 other migrants. The study was restricted to migrants from regions with at least 1,000 refugees living in Sweden, which included the Middle East and North Africa, sub-Saharan Africa and Eastern Europe and Russia. After adjusting for confounders, the researchers were able to delineate how rates of substance use disorders changed depending on how old people were when they first immigrated to Sweden, how long they had lived in Sweden and whether they were diagnosed with post-traumatic stress disorder (PTSD).

Half the risk

The researchers found that the risk of substance use disorders in refugees and other migrants was about half that of the Swedish-born population. Both migrant groups were less likely to be diagnosed with both alcohol and polydrug addiction, although differences in cannabis use disorders compared with the Swedish-born population were less pronounced. There were no discernable differences in addiction rates between refugees who fled to Sweden and migrants who moved to the country on their own terms.

Interestingly, the longer the refugees and migrants stayed in Sweden and the younger they were when they first moved to the country, the greater the risk of substance addiction became. After 10 years or more in Sweden, it was on par with the native population. People who arrived before the age of 6 were also significantly more likely to suffer from substance abuse than those who arrived when they were older. When it came to individuals diagnosed with PTSD, all groups were more likely to have a substance use disorder than those without PTSD, although Swedes were overrepresented here as well.

Possible interpretations

“There are a number of possible interpretations for our findings,” says Anna-Clara Hollander, research coordinator at the Department of Public Health Sciences at Karolinska Institutet, and one of the study’s authors. “One is that acculturative processes lead some migrant groups to adopt Swedish health behaviors over time, thus increasing the risk of being diagnosed with a substance use disorder. Alternatively, migrants who have lived longer in Sweden may be more likely to use the Swedish secondary healthcare system, due to better health literacy or fewer language barriers. Further studies are required to disentangle the multifactorial influences that may underlie these results.”

The researchers note that a limitation of the study is that migrants sometimes face obstacles to accessing healthcare such as language, gender or stigma-based barriers.

The findings add to a body of research showing that refugees and migrants initially tend to have a lower risk of self-harming behavior, such as substance addiction and suicide, but that they over time converge toward rates seen in the host country. Another recent study by Karolinska Institutet and UCL showed that the risk of suicide for both refugees and migrants increased over time and was after 20 years almost the same as for the Swedish-born population.

“Our study illustrates the substantial burden of mental health problems attributable to substance use disorders in the general population,” says James B. Kirkbride, psychiatric epidemiologist at the Division of Psychiatry at UCL, and the study’s lead author. “If generalizable, such high levels of psychiatric morbidity and potential convergence of rates in migrant groups over time to those in the background population present a fundamental public health concern for many nations across the globe.”

Funding for this study was provided by the Wellcome Trust, the Royal Society, Mental Health Research UK, UCLH NIHR Biomedical Research Centre, a UCL Overseas Research Scholarship, the Public Health Agency of Sweden and the Swedish Research Council for Health, Working Life and Welfare (FORTE).

Publication

“Substance use disorders in refugee and migrant groups in Sweden: A nationwide cohort study of 1.2 million people,” Samantha Harris, Jennifer Dykxhoorn, Anna-Clara Hollander, Christina Dalman, James B. Kirkbride, PLOS Medicine, November 5, 2019, DOI: 10.1371/journal.pmed.1002944