Poverty in adolescence is associated with later drug use. Few studies have evaluated the role of adolescent psychiatric disorders in this association.

This study aimed to investigate mediation and interaction simultaneously, enabling the disentanglement of the role of adolescent psychiatric disorders in the association between poverty in adolescent and later drug use disorders.

A national cohort study of 634 223 individuals born in 1985–1990, residing in Sweden between the ages of 13 and 18 years, was followed from age 19 years until the first in-patient or out-patient care visit with a diagnosis of drug use disorder. A four-way decomposition method was used to determine the total effect of the association with poverty and possible mediation by and/or interaction with diagnosis of adolescent psychiatric disorders.

The hazard ratios for drug use disorders among those experiencing poverty compared with those ‘never in poverty’ were 1.40 (95% CI, 1.32–1.63) in females and 1.43 (95% CI, 1.37–1.49) in males, after adjusting for domicile, origin and parental psychiatric disorders. Twenty-four per cent of this association in females, and 13% in males, was explained by interaction with and/or mediation by adolescent psychiatric disorders.

Part of the association between poverty in adolescence and later drug use disorders was due to mediation by and/or interaction with psychiatric disorders. Narrowing socioeconomic inequalities in adolescence might help to reduce the risks of later drug use disorders. Interventions aimed at adolescents with psychiatric disorders might be especially important.

People with substance use disorders have a well-known increased risk for taking their own life. Previous research has mainly focused on suicide in mental health services, whereas there is limited knowledge regarding suicide after contact with substance misuse services.

The aim of the current study was to describe the utilisation of both mental health services and substance misuse services among people who have died by suicide within a year of contact with substance misuse services.

We used an explanatory observational design, where all suicide deaths in the period from 2009 to 2016 were retrieved from the Norwegian Cause of Death Registry and linked with the Norwegian Patient Registry. The people who had been in contact with substance misuse services within a year before their death were included in the sample (n = 419). The analysis was stratified by gender, and variables with significant differences between men and women were entered into a multivariate logistic regression model.

More women (73.5%) than men (60.6%) had contact with mental health services in their last year (P = 0.01). In the adjusted logistic regression model, poisoning was more common among women (adjusted odds ratio (AOR) = 1.81, 95% CI 1.09–3.02) and women were more likely to be diagnosed with a sedative, hypnotic or anxiolytic use disorder (F14) in their last year (AOR = 2.77, 95% CI 1.37–5.68).

This study highlights gender differences for suicide in substance misuse services, and the importance of collaboration and cooperation between substance misuse services and mental health services.

Although the association between attention-deficit/hyperactivity disorder (ADHD) and drug use disorder (DUD) is well documented, it is unclear whether it is causal or results from familial confounding.

In this study we included all 551 164 individuals born in Sweden between 1991 and 1995 and used linked data from multiple nationwide registries to identify those with ADHD prior to age 15 years (1.71%). We used Cox proportional hazards models to investigate the future risk for DUD as a function of an ADHD registration and then compared the results from the entire population with the results from a co-relative design. Using the Swedish Multi-Generation Register, we identified all full-sibling, half-sibling and first-cousin pairs discordant for ADHD.

In the population sample, ADHD had a substantially increased risk for future DUD with a hazard ratio (HR) of 3.34 after accounting for gender and parental education. Examining discordant cousin pairs, discordant half-siblings and discordant siblings, those with ADHD had HRs for DUD of 3.09, 2.10 and 2.38 respectively. Controlling for the number of ADHD registrations, ADHD patients with and without stimulant treatment were similarly associated with later DUD risk.

ADHD diagnosed before 15 years of age was strongly related to future risk for DUD. The magnitude of this association was modestly reduced in relative pairs discordant for ADHD, suggesting that the ADHD–DUD association is partly causal and partly a result of familial confounding. We found no evidence to suggest that this association resulted from stimulant treatment.