Background. Previous Scandinavian studies have shown increased levels of psychiatric morbidity in young refugees and international adoptees with an origin outside Europe. This study investigated their risk of non-affective psychotic disorders (NAPD) and whether this risk is influenced by early childhood adversity, operationalised as age at adoption/residency, and/or gender.

Methods. Register study in Swedish national cohorts born 1972-1990 including 21 615 non-European international adoptees, 42 732 non-European refugees that settled in Sweden at age 0-14 years and 1 610 233 Swedish born. The study population was followed from age 18 to year 2016 for hospitalisations with a discharge diagnosis of NAPD. Hazard ratios (HRs) were calculated in gender stratified Cox regression models, adjusted for household income at age 17.

Results. The adjusted risks of NAPD were 2.33 [95% confidence interval (CI) 2.07-2.63] for the international adoptees and 1.92 (1.76-2.09) for the former child refugees, relative to the Swedish-born population. For the international adoptees there was a stepwise gradient for NAPD by age of adoption from adjusted HR 1.66 (1.29-2.03) when adopted during the first year of life to adjusted HR 4.56 (3.22-6.46) when adopted at ages 5-14 years, with a similar risk pattern in women and men. Age at residency did not influence the risk of NAPD in the refugees, but their male to female risk ratio was higher than in Swedish-born and the adoptees.

Conclusion. The risk pattern in the international adoptees gives support to a link between early childhood adversity and NAPD. Male gender increased the risk of NAPD more among the refugees.