Drug use Disorder (DUD), the risk for which is substantially influenced by both genetic and social factors, is geographically concentrated in high-risk regions. An important step toward understanding this pattern is to examine geographical distributions of the genetic liability to DUD and a key demographic risk factor – social deprivation.

We calculated the mean family genetic risk score (FGRS) for DUD ((FGRSDUD) and social deprivation for each of the 5983 areas Demographic Statistical Areas (DeSO) for all of Sweden and used geospatial techniques to analyze and map these factors.

Using 2018 data, substantial spatial heterogeneity was seen in the distribution of the genetic risk for DUD in Sweden as a whole and in its three major urban centers which was confirmed by hot-spot analyses. Across DeSOs, FGRSDUD and s.d. levels were substantially but imperfectly correlated (r = + 0.63), with more scattering at higher FGRSDUD and s.d. scores. Joint mapping across DeSOs for FGRSDUD and s.d. revealed a diversity of patterns across Sweden. The stability of the distributions of FGRSDUD and s.d. in DeSOs within Sweden over the years 2012–2018 was quite high.

The geographical distribution of the genetic risk to DUD is quite variable in Sweden. DeSO levels of s.d. and FRGSDUD were substantially correlated but also disassociated in a number of regions. The observed patterns were largely consistent with known trends in the human geography of Sweden. This effort lays the groundwork for further studies of the sources of geographic variation in rates of DUD.

Robust clinical indices of etiologic heterogeneity for psychiatric disorders are rare. We investigate whether age at onset (AAO) reflects genetic heterogeneity, utilizing Genetic Risk Ratios (GRR) derived from Family Genetic Risk Scores (FGRS).

We examined, in individuals born in Sweden 1940–2003, whether AAO for five primary disorders -- drug use disorder (DUD), alcohol use disorder (AUD), major depression (MD), bipolar disorder (BD), and schizophrenia (SZ)-- was associated with varying levels of GRRs with a range of informative secondary disorders and traits.

Our disorders displayed a varying pattern of change of GRRs with increasing AAO. At one end was SZ, where all GRRs rose with increasing AAO meaning that SZ became increasing genetically heterogeneous with later AAO. The most balanced disorder was AUD where, with increasing AAO, GRRs rose for AD, BD, and MD and declined for DUD, CB, and ADHD. That is, at young AAO, AUD had high levels of genetic risk for other externalizing disorders while at older AAO, high genetic risk for internalizing disorders were more prominent. MD was at the continuum's other end where all GRRs, except for AD, decreased with higher AAO, meaning that MD became increasingly genetically homogeneous with later AAO.

Genetic heterogeneity was robustly associated with AAO across our five primary disorders with substantial inter-disorder differences in the observed patterns. In particular, young AAO was associated with maximal genetic homogeneity for SZ and DUD while older AAO had greater genetic homogeneity for MD with AUD falling in between.

The concept of schizotypal personality disorder (SPD) emerged from observations of personality characteristics common in relatives of schizophrenic patients. While often studied in family designs, few studies and none with genetic measures, have examined SPD in epidemiological samples.

We studied individuals born in Sweden 1940–2000 with an ICD-10 diagnosis of SPD with no prior schizophrenia (SZ) diagnosis (n = 2292). Demographic features, patterns of comorbidity, and Family Genetic Risk Scores (FGRS) were assessed from multiple Swedish registries. Prediction of progression to SZ was assessed by Cox models.

SPD was rare, with a prevalence of 0.044%, and had high levels of comorbidity with autism spectrum disorder (ASD), OCD, ADHD, and major depression (MD), and increased rates of being single, unemployed and in receipt of welfare. Affected individuals had elevated levels of FGRS for SZ (+0.42), ASD (+0.30), MD (+0.29), and ADHD (+0.20). Compared to cases of schizophrenia, they had significantly lower rates of FGRSSZ, but significantly elevated rates of genetic risk for ASD, MD, and ADHD. Over a mean follow-up of 8.7 years, 14.6% of SPD cases received a first diagnosis of SZ, the risk for which was significantly increased by levels of FGRSSZ, male sex, young age at SPD diagnosis and an in-patient SPD diagnosis and significantly decreased by comorbidity with MD, ASD, and ADHD.

Our results not only support the designation of SPD as a schizophrenia spectrum disorder but also suggest potentially important etiologic links between SPD and ASD and, to a lesser extent, ADHD, OCD, and MD.

One potential cause of comorbidity is the direct causal effect of one disorder – A – on risk for subsequent onset of disorder B. Could genetic risk scores be utilized to test for such an effect? If disorder A causally impacts on risk for disorder B, then genetic risk for disorder A should be lower in cases of disorder A with v. without a prior onset of B.

In all individuals (n = 905 736) born in Sweden from 1980 to 1990, from six psychiatric and drug use disorders (major depression, anxiety disorders, alcohol use disorder, drug use disorder, bipolar disorder, and schizophrenia), we formed 14 pairs of disorders A and B. In these pairs, we compared, using Cox proportional hazards models, the predictive effect of the familial-genetic risk score (FGRS) for disorder B in those who had v. had not had a prior onset of disorder A.

In all pairs, the impact of the FGRS for disorder B was significantly stronger in cases without v. with a prior history of disorder A. These effects were similar across sex, stable across levels of FGRS and not likely due to clinician bias. In many of our disorder pairs, previous clinical studies suggest a mechanism for a causal effect of disorder A on B.

Our findings provide indirect evidence that the occurrence of one psychiatric or substance use disorder often has a causal effect on risk for subsequent disorders. This mechanism may substantially contribute to the widespread comorbidity among psychiatric conditions.

Prior research has reported an association between divorce and suicide attempt. We aimed to clarify this complex relationship, considering sex differences, temporal factors, and underlying etiologic pathways.

We used Swedish longitudinal national registry data for a cohort born 1960–1990 that was registered as married between 1978 and 2018 (N = 1 601 075). We used Cox proportional hazards models to estimate the association between divorce and suicide attempt. To assess whether observed associations were attributable to familial confounders or potentially causal in nature, we conducted co-relative analyses.

In the overall sample and in sex-stratified analyses, divorce was associated with increased risk of suicide attempt (adjusted hazard ratios [HRs] 1.66–1.77). Risk was highest in the year immediately following divorce (HRs 2.20–2.91) and declined thereafter, but remained elevated 5 or more years later (HRs 1.41–1.51). Divorcees from shorter marriages were at higher risk for suicide attempt than those from longer marriages (HRs 3.33–3.40 and 1.20–1.36, respectively). In general, HRs were higher for divorced females than for divorced males. Co-relative analyses suggested that familial confounders and a causal pathway contribute to the observed associations.

The association between divorce and risk of suicide attempt is complex, varying as a function of sex and time-related variables. Given evidence that the observed association is due in part to a causal pathway from divorce to suicide attempt, intervention or prevention efforts, such as behavioral therapy, could be most effective early in the divorce process, and in particular among females and those whose marriages were of short duration.

It is clinically important to predict the conversion of major depression (MD) to bipolar disorder (BD). Therefore, we sought to identify related conversion rates and risk factors.

This cohort study included the Swedish population born from 1941 onward. Data were collected from Swedish population-based registers. Potential risk factors, including family genetic risk scores (FGRS), which were calculated based on the phenotypes of relatives in the extended family and not molecular data, and demographic/clinical characteristics from these registers were retrieved. Those with first MD registrations from 2006 were followed up until 2018. The conversion rate to BD and related risk factors were analyzed using Cox proportional hazards models. Additional analyses were performed for late converters and with stratification by sex.

The cumulative incidence of conversion was 5.84% [95% confidence interval (95% CI) 5.72–5.96] for 13 years. In the multivariable analysis, the strongest risk factors for conversion were high FGRS of BD [hazard ratio (HR) = 2.73, 95% CI 2.43–3.08], inpatient treatment settings (HR = 2.64, 95% CI 2.44–2.84), and psychotic depression (HR = 2.58, 95% CI 2.14–3.11). For late converters, the first registration of MD during the teenage years was a stronger risk factor when compared with the baseline model. When the interactions between risk factors and sex were significant, stratification by sex revealed that they were more predictive in females.

Family history of BD, inpatient treatment, and psychotic symptoms were the strongest predictors of conversion from MD to BD.

To clarify, in a national sample, associations between risk for seven psychiatric and substance use disorders and five key transitions in Sweden's public educational system.

Swedish-born individuals (1972–1995, N = 1 997 910) were followed through 12-31-2018, at mean age 34.9. We predicted, from these educational transitions, risk for major depression (MD), obsessive-compulsive disorder (OCD), bipolar disorder (BD), schizophrenia (SZ), anorexia nervosa (AN), alcohol use disorder (AUD), and drug use disorder (DUD), assessed from Swedish national registers, by Cox regression, censoring individuals with onsets ⩽17. We also predicted risk from the deviation of grades from family-genetic expectations (deviation 1) and from changes in grades from ages 16 to 19 (deviation 2).

We observed four major risk patterns across transitions in our disorders: (i) MD and BD, (ii) OCD and SZ, (iii) AUD and DUD, and (iv) AN. Failing early educational transitions had the greatest impact on risk for OCD and SZ while for other disorders, not progressing from basic to upper high school had the largest effect. Completing vocational v. college-prep upper high school was strongly associated with risk for AUD and DUD, had little relation with MD, OCD, BD, and SZ risk, and was protective for AN. Deviation 1 predicted risk most strongly for SZ, AN, and MD. Deviation 2 predicted risk most strongly for SZ, AUD, and DUD.

The pattern of educational transitions and within family and within person development deviations are strongly and relatively specifically associated with future risk for seven psychiatric and substance-use disorders.

Suicidal behavior and substance use disorders (SUDs) are important public health concerns. Prior suicide attempts and SUDs are two of the most consistent predictors of suicide death, and clarifying the role of SUDs in the transition from suicide attempt to suicide death could inform prevention efforts.

We used national Swedish registry data to identify individuals born 1960–1985, with an index suicide attempt in 1997–2017 (N = 74 873; 46.7% female). We assessed risk of suicide death as a function of registration for a range of individual SUDs. We further examined whether the impact of SUDs varied as a function of (i) aggregate genetic liability to suicidal behavior, or (ii) age at index suicide attempt.

In univariate models, risk of suicide death was higher among individuals with any SUD registration [hazard ratios (HRs) = 2.68–3.86]. In multivariate models, effects of specific SUDs were attenuated, but remained elevated for AUD (HR = 1.86 95% confidence intervals 1.68–2.05), opiates [HR = 1.58 (1.37–1.82)], sedatives [HR = 1.93 (1.70–2.18)], and multiple substances [HR = 2.09 (1.86–2.35)]. In secondary analyses, the effects of most, but not all, SUD were exacerbated by higher levels of genetic liability to suicide death, and among individuals who were younger at their index suicide attempt.

In the presence of a strong predictor of suicide death – a prior attempt – substantial predictive power is still attributable to SUDs. Individuals with SUDs may warrant additional suicide screening and prevention efforts, particularly in the context of a family history of suicidal behavior or early onset of suicide attempt.

Among individuals with alcohol use disorder (AUD) and drug use disorder (DUD), is their genetic liability and its specificity moderated by substance availability?

Offspring (born 1960–1995) and their biological parents from three family types [not-lived-with (NLW) biological father, mother and adoptive] and their AUD and DUD diagnoses were ascertained from Swedish national registers. Parent–offspring resemblance was calculated by tetrachoric correlation.

In Swedes born from 1960 to 1995, prevalence rates of AUD were stable while DUD rates increased substantially. Best-estimate tetrachoric correlations (±95% confidence intervals) between AUD in biological parents and AUD and DUD in their offspring were, respectively, +0.19 (0.18–0.20) and +0.18 (0.17–0.20). Parallel results from DUD in parents to AUD and DUD in children were +0.12 (0.10–0.13) and +0.27 (0.26–0.28). When divided into older and younger cohorts, the specificity of DUD transmission increased substantially over time, while the genetic correlation between AUD and DUD significantly decreased.

Raised when alcohol was the preferred substance of abuse and illicit drugs highly stigmatized, AUD in parents reflected a general liability to substance use disorders, as they transmitted similar genetic risk for AUD and DUD to their children raised when both substances were widely available and relatively acceptable. DUD in parents, by contrast, reflected a more specific liability to DUD and, when transmitted to offspring, produced a considerably stronger risk for DUD than for AUD that increased over time. The magnitude and specificity of the genetic liability to psychoactive substances can be influenced by the availability of that substance.

Despite a large descriptive literature linking creativity and risk for psychiatric illness, the magnitude and specificity of this relationship remain controversial.

We examined, in 1 137 354 native Swedes with one of 59 3-digit official and objective occupational codes in managerial and educated classes, their familial genetic risk score (FGRS) for ten major disorders, calculated from 1st through 5th degree relatives. Mean FGRS across disorders were calculated, in 3- and 4-digit occupational groups, and then controlled for those whose disorder onset preceded occupational choice. Using sequential analyses, p values were evaluated using Bonferroni correction.

3-digit professions considered to reflect creativity (e.g. ‘artists’ and ‘authors’) were among those with statistically significant elevations of FGRS. Among more specific 4-digit codes, visual artists, actors, and authors stood out with elevated genetic risks, highest for major depression (MD), anxiety disorders (AD) and OCD, more modest for bipolar disorders (BD) and schizophrenia and, for authors, for drug and alcohol use disorders. However, equal or greater elevations in FGRS across disorders were seen for religious (e.g. ministers), helping (e.g. psychologists, social workers), and teaching/academic occupations (e.g. professors). The potential pathway from FGRS → Disorder → Occupation accounts for a modest proportion of the signal, largely for MD and AD risk.

While traditional creative occupations were associated with elevated genetic risk for a range of psychiatric disorders, this association was not unique, as similar, or greater elevations were seen for religious, helping and teaching professions and was stronger for internalizing than psychotic disorders.

Functional somatic disorders (FSD) feature medical symptoms of unclear etiology. Attempts to clarify their origin have been hampered by a lack of rigorous research designs. We sought to clarify the etiology of the FSD by examining the genetic risk patterns for FSD and other related disorders.

This study was performed in 5 829 186 individuals from Swedish national registers. We quantified familial genetic risk for FSD, internalizing disorders, and somatic disorders in cases of chronic fatigue syndrome (CFS), fibromyalgia (FM), and irritable bowel syndrome (IBS), using a novel method based on aggregate risk in first to fifth degree relatives, adjusting for cohabitation. We compared these profiles with those of a prototypic internalizing psychiatric – major depression (MD) – and a somatic/autoimmune disorder: rheumatoid arthritis (RA).

Patients with FM carry substantial genetic risks not only for FM, but also for pain syndromes and internalizing, autoimmune and sleep disorders. The genetic risk profiles for IBS and CFS are also widely distributed although with lower average risks. By contrast, genetic risk profiles of MD and RA are much more restricted to related conditions.

Patients with FM have a relatively unique family genetic risk score profile with elevated genetic risk across a range of disorders that differs markedly from the profiles of a classic autoimmune disorder (RA) and internalizing disorder (MD). A similar less marked pattern of genetic risks was seen for IBS and CFS. FSD arise from a distinctive pattern of genetic liability for a diversity of psychiatric, autoimmune, pain, sleep, and functional somatic disorders.

Do genetic risk profiles for drug use disorder (DUD), major depression (MD), and attention-deficit hyperactivity disorder (ADHD) differ substantially as a function of sex, age at onset (AAO), recurrence, mode of ascertainment, and treatment?

Family genetic risk scores (FGRS) for MD, anxiety disorders, bipolar disorder, schizophrenia, alcohol use disorder, DUD, ADHD, and autism-spectrum disorder were calculated from 1st–5th degree relatives in the Swedish population born 1932–1995 (n = 5 829 952). Profiles of these FGRS were obtained and compared across various subgroups of DUD, MD, and ADHD cases.

Differences in FGRS profiles for DUD, MD, and ADHD by sex were modest, but they varied substantially by AAO, recurrence, ascertainment, and treatment with scores typically higher in cases with greater severity (e.g. early AAO, high recurrence, ascertainment in high intensity clinical settings, and treatment). However, severity was not always related to purer genetic profiles, as genetic risk for many disorders often increased together. However, some results, such as by mode of ascertainment from different Swedish registries, produced qualitative differences in FGRS profiles.

Differences in FGRS profiles for DUD, MD, and ADHD varied substantially by AAO, recurrence, ascertainment, and treatment. Replication of psychiatric studies, particularly those examining genetic factors, may be difficult unless cases are matched not only by diagnosis but by important clinical characteristics. Genetic correlations between psychiatric disorders could arise through one disorder impacting on the patterns of ascertainment for the other, rather than from the direct effects of shared genetic liabilities.

Does the genetic aptitude for educational attainment (GAEA) moderate the genetic risk for alcohol use disorder (AUD) and drug use disorder (DUD)?

In the native Swedish population, born 1960–1980 and followed through 2017 (n = 1 862 435), the family genetic risk score (FGRS) for AUD and DUD and GAEA were calculated from, respectively, the educational attainment and risk for AUD and DUD, of 1st through 5th degree relatives from Swedish national registers. Analyses utilized Aalen's linear hazards models.

Risk for AUD was robustly predicted by the main effects of FGRSAUD [b = 6.32 (95% CI 6.21–6.43), z = 64.9, p < 0.001) and GAEA [b = −2.90 (2.83–2.97), z = 44.1, p < 0.001] and their interaction [b = −1.93 (1.83–2.03), z = 32.9, p < 0.001]. Results were similar for the prediction of DUD by the main effects of FGRSDUD [b = 4.65 (CI 4.56–4.74), z = 59.4, p < 0.001] and GAEA [−2.08 (2.03–2.13), z = 46.4, p < 0.001] and their interaction [b = −1.58 (1.50–1.66)), z = 30.2, p < 0.001]. The magnitude of the interactions between GAEA and FGRSAUD and FGRSDUD in the prediction of, respectively, AUD and DUD was attenuated only slightly by the addition of educational attainment to the model.

The genetic propensity to high educational attainment robustly moderates the genetic risk for both AUD and DUD such that the impact of the genetic liability to AUD and DUD on the risk of illness is substantially attenuated in those with high v. low GAEA. This effect is not appreciably mediated by the actual level of educational attainment. These naturalistic findings could form the basis of prevention efforts in high-risk youth.

– Comorbidity between psychiatric disorders is extensive but, from a genetic perspective, still poorly understood. Modern molecular genetic approaches to this problem are limited by a reliance on case–control designs.

– In 5 828 760 individuals born in Sweden from 1932–1995 with a mean (s.d.) age at follow-up of 54.4 (18.1), we examined family genetic risk score (FGRS) profiles including internalizing, psychotic, substance use and developmental disorders in 10 pairs of psychiatric and substance use disorders diagnosed from population registries. We examined these profiles in three groups of patients: disorder A only, disorder B only and comorbid cases with both disorders.

– The most common pattern of findings, seen in five pairings, was simple and quantitative. Comorbid cases had higher FGRS than both non-comorbid cases for all (or nearly all) disorders. However, the pattern was more complex in the remaining five pairings and included qualitative changes where the comorbid cases showed no increases in FGRS for certain disorders and in a few cases significant decreases. Several comparisons showed an asymmetric pattern of findings with increases, in comorbidity compared to single disorder cases, of the FGRS for only one of the two disorders.

– The examination of FGRS profiles in general population samples where all disorders are assessed in all subjects provides a fruitful line of inquiry to understand the origins of psychiatric comorbidity. Further work will be needed, with an expansion of analytic approaches, to gain deeper insights into the complex mechanisms likely involved.

Previous studies have demonstrated substantial associations between substance use disorders (SUD) and suicidal behavior. The current study empirically assesses the extent to which shared genetic and/or environmental factors contribute to associations between alcohol use disorders (AUD) or drug use disorders (DUD) and suicidal behavior, including attempts and death.

The authors used Swedish national registry data, including medical, pharmacy, criminal, and death registrations, for a large cohort of twins, full siblings, and half siblings (N = 1 314 990) born 1960–1980 and followed through 2017. They conducted twin-sibling modeling of suicide attempt (SA) or suicide death (SD) with AUD and DUD to estimate genetic and environmental correlations between outcomes. Analyses were stratified by sex.

Genetic correlations between SA and SUD ranged from rA = 0.60–0.88; corresponding shared environmental correlations were rC = 0.42–0.89 but accounted for little overall variance; and unique environmental correlations were rE = 0.42–0.57. When replacing attempt with SD, genetic and shared environmental correlations with AUD and DUD were comparable (rA = 0.48–0.72, rC = 0.92–1.00), but were attenuated for unique environmental factors (rE = −0.01 to 0.31).

These findings indicate that shared genetic and unique environmental factors contribute to comorbidity of suicidal behavior and SUD, in conjunction with previously reported causal associations. Thus, each outcome should be considered an indicator of risk for the others. Opportunities for joint prevention and intervention, while limited by the polygenic nature of these outcomes, may be feasible considering moderate environmental correlations between SA and SUD.

Alcohol use disorder (AUD) is clinically heterogeneous. We examine its potential genetic heterogeneity as a function of sex, age, clinical features and mode of ascertainment.

In the Swedish population born 1932–1995 (n = 5 829 952), we examined the genetic risk profiles for AUD, major depression (MD), anxiety disorders, bipolar disorder, drug use disorder (DUD), attention deficit-hyperactivity disorder (ADHD) and criminal behavior (CB) in 361 124 cases of AUD subdivided by sex, age at onset (AAO), recurrence, mode of ascertainment and medical complications. Family genetic risk scores (FGRS), calculated from 1st to 5th-degree relatives controlling of cohabitation, assesses genetic risk from phenotypes in the family, not from DNA variants.

FGRS profiles differed modestly across sex with all scores higher in females. Differences were more pronounced for AAO and recurrence with the FGRS for AUD, DUD, ADHD and CB substantially higher in cases with early AAO or high recurrence rates. Genetic profiles differed considerably by mode of ascertainment, with higher FGRS for AUD and most other disorders in patients seen in hospital v. primary care settings. Cases of AUD with medical complications had higher FGRS for AUD. AUD cases comorbid with MD and DUD had higher FGRS risk for AUD, but this genetic may be less specific given increases in FGRS for multiple other disorders.

From a genetic perspective, AUD differs substantially as a function of AAO, recurrence, mode of ascertainment and patterns of comorbidity, suggesting caution in cross-sample comparisons of AUD cohorts that differ in these features.

How does genetic liability to suicide attempt (SA), suicide death (SD), major depression (MD), bipolar disorder (BD), schizophrenia (SZ), alcohol use disorder (AUD), and drug use disorder (DUD) impact on risk for SA and SD?

In the Swedish general population born 1932–1995 and followed through 2017 (n = 7 661 519), we calculate family genetic risk scores (FGRS) for SA, SD, MD, BD, SZ, AUD, and DUD. Registration for SA and SD was assessed from Swedish national registers.

In univariate and multivariate models predicting SA, FGRS were highest for SA, AUD, DUD, and MD. In univariate models predicting SD, the strongest FGRS were AUD, DUD, SA, and SD. In multivariate models, the FGRS for SA and AUD were higher in predicting SA while the FGRS for SD, BD, and SZ were higher in predicting SD. Higher FGRS for all disorders significantly predicted both younger age at first SA and frequency of attempts. For SD, higher FGRS for MD, AUD, and SD predicted later age at SD. Mediation of FGRS effects on SA and SD was more pronounced for SD than SA, strongest for AUD, DUD, and SZ FGRS and weakest for MD.

FGRS for both SA and SD and for our five psychiatric disorders impact on risk for SA and SD in a complex manner. While some of the impact of genetic risk factors for psychiatric disorders on risk for SA and SD is mediated through developing the disorders, these risks also predispose directly to suicidal behaviors.

Although alcohol use disorder (AUD) runs strongly within families, studies examining the impact of rearing environment, unconfounded by genetic effects, are rare and, to date, contradictory. We here seek to conduct such a study using an adoptive co-sib control design.

Defining high-risk as having ⩾1 biological parent with an externalizing syndrome (AUD, drug abuse or crime), we identified 1316 high-risk full-sibships and 4623 high-risk half-sibships containing at least one member who was home-reared and one who was adopted-away. Adoptive families are carefully screened in Sweden to provide high-quality rearing environment for adoptees. AUD was assessed from national medical, criminal and pharmacy registries.

Controlling for sex, parental age at birth, and, for half-siblings, affection status of the non-shared parent, hazard ratios (±95% CI) for AUD in the matched adopted v. home-reared full- and half-siblings were, respectively, 0.76 (0.65–0.89) and 0.77 (0.70–0.84). The protective effect of adoption on AUD risk was stronger in the full- and half-sibling pairs with very high familial liability (two high-risk parents) and significantly weaker when the adoptive family was broken by death or divorce or contained a high-risk adoptive parent.

In both full- and half-sibling pairs, we found evidence that the rearing environment substantially impacts on the risk for AUD. High-quality rearing environments can meaningfully reduce the risk for AUD, especially in those at high familial risk.

We sought to quantify and investigate the causal nature of the association between resilience at age 18 and future drug abuse (DA).

In a national sample of Swedish men (n = 1 392 800), followed for a mean of 30.3 years, resilience was assessed during military conscription and DA defined from medical, criminal and pharmacy registers. For causal inference, we utilized three methods: (i) instrumental variable analyses with the month of birth as the instrument; (ii) co-relative analyses using the general population, cousins, siblings and monozygotic twins; and (iii) propensity scoring on a subsample (n = 48 548) with strong resilience predictors. Cox proportional hazards models were utilized to examine survival time till DA diagnosis.

Low resilience was most robustly predicted from internalizing symptoms. Lower levels of standardized resilience strongly predicted the risk for DA (HR = 2.31, 95% CIs 2.28–2.33). In instrumental, co-relative, and propensity score analyses, the association between resilience and DA was estimated at HR = 3.06 (2.44–3.85), 1.34 (1.28–1.39), and 1.40 (1.28–1.53), respectively. Sensitivity analyses suggested that our instrument was weak and, despite our large sample, likely under-estimated confounding.

Low resilience strongly predicts DA risk. Three different causal analysis methods, with divergent assumptions, concurred in estimating that an appreciable proportion of this association was causal, probably around 40%, with the remainder arising from confounding variables many of which are likely familial. Consistent with prior interventions focused on substance use prevention, our results suggest that prevention programs that increase resilience in adolescence should meaningfully reduce the long-term risk for DA.