Exploring the Roots of Violence Risk in Schizophrenia: evaluating current perspectives

A short review of current research on the subject, submitted as one of my course’s essays at King’s.

Schizophrenia spectrum disorders (SSD) comprise complex diagnoses, ranging from the less severe forms to the more severe ones, respectively — delusional disorder, brief psychotic disorder, schizophreniform disorder, schizophrenia, and schizoaffective disorder (Bhati, 2013). Evidence suggests an association between SSD and an increased risk of perpetrating violence (Brennan et al., 2000; Wallace et al., 2004). Nevertheless, conflicting results remain among such studies due to the less explored mechanisms underlying the association (Brennan et al., 2000; Walsh et al., 2002). Thus, studies have attempted to identify several significant moderating variables related to the association between the two.

For instance, studies found that substance misuse seems to significantly contribute to the association between violence and individuals with SSD (Wallace et al., 2004; Fazel et al., 2009a). Another factor that past studies have examined is deleterious childhood environments — particularly childhood maltreatment to a heightened risk of offending (Lau et al., 2021; Ranu et al., 2023). In comparison, others looked at developmental factors such as poverty, familial history of criminality, developmental delays, and truancy (Mullen, 2006; Pickett & Wilkinson, 2015). However, due to the variability in research methodologies, small sample sizes, and the risk of stigmatising individuals with SSD, more literature needs to scrutinise these findings (Fusar-Poli et al., 2022). The present essay shall critically examine these identified confounders and weigh in on the state-of-the-art literature on the subject. It shall go over the risk of perpetrating violence amongst said population in the presence of these confounders, respectively: (1) substance misuse, (2) deleterious childhood environments and previous victimisation experiences, and (3) social class.

Firstly, research investigating the mediating role of substance misuse and violence among SSD individuals is abundant; especially in attenuating negative symptoms (e.g. blunted affect, alogia), and results are generally consistent (Baeza et al., 2009; Baldacchino et al., 2012). However, results remain inconsistent for positive symptoms (e.g., hallucinations, delusions) that are intimately associated with violence (Bjørkly, 2002; Fazel et al., 2009a). To illustrate, a recent meta-analysis in 15 countries with over 15000 male and female participants found a strong association between substance misuse and a higher risk of perpetrating violence in individuals with SSD compared to the general population. In particular, the odds of perpetrating violence among such individuals were around 10-fold compared to controls, whereas the number was 3-fold for SSD participants without comorbid substance misuse (Whiting et al., 2022). Additionally, Wallace et al.’s (2004) cohort study (N=2861) over 25 years also supports the previous results — in which SSD patients with substance misuse have significantly higher rates of criminal convictions compared to those without (68.1% vs 11.7%).

Nevertheless, Fazel et al.’s (2009b) systematic-review emphasised how the risk of perpetrating violence among SSD individuals with substance misuse is no different from those presenting only with substance misuse diagnoses. Therefore, SSD did not appear to perpetuate violence risks. Additionally, the previous studies have limitations, namely heterogeneity across studies, overreliance on clinical diagnoses as opposed to research criteria, and they mainly consider convictions — which may underestimate the actual prevalence of violent behaviours. Furthermore, other factors associated with substance misuse may contribute to the association, hence the need to do more research which looks at the mechanisms behind them (Brennan et al., 2000; Wallace et al., 2004; Whiting et al., 2022).

Secondly, to better understand the mechanism behind violence perpetration among SSD individuals, past studies have looked at adverse childhood experiences, in particular maltreatment and victimisation. However, only a few studies have explored the association (Green et al., 2018; Ranu et al., 2023). The initial meta-analysis, which includes 11 studies on the subject (N=2215), found that SSD individuals who reported historical maltreatment were approximately twice as likely to commit violence than those without such experiences (OR=2.46) (Green et al., 2018). The rationale for this association may be due to mechanisms of neurological processing, stress reactivity, and risky health behaviours that contribute to an increased sense of threat or persecution, thereby mediating the development of psychoses. Additionally, a meta-analysis on the subject that (1) extended the comparison to violent individuals without psychosis and healthy controls and (2) employed a wider range of adverse childhood experiences suggest adverse experiences in childhood might significantly contribute to violence among SSD individuals (Ranu et al., 2023).

Indeed, deleterious childhood experiences may contribute to lifelong patterns that could lead to violence perpetration among SSD individuals, but it should consider factors mediating the relationship (Swanson et al., 2002). For instance, regarding victimisation, previous research identified a hierarchy within the relationship — in which those who experienced abuse (physical and sexual) before the age of 16 but were not victimised in adulthood were no more likely to become violent in later years. In contrast, those who reported victimisation as adults but reported no maltreatment during childhood were more likely to commit violent perpetration in adulthood. Finally, those who experienced victimisation both in childhood and adulthood were most likely to become violent (Swanson et al., 2002; Ranu et al., 2023). Thus, the association of repeated victimisation with violence perpetration was significant for SSD men and women when considering these factors. Nevertheless, weaknesses for the previous findings were the majority of male samples, methodological constraints such as varied tools in measuring actual violence, and the need for further research that addresses mediating mechanisms such as brain effects, attachment disorders, behavioural patterns, and socio-environmental context (Ranu et al., 2023).

Thirdly, regarding socio-environmental context, social class — particularly poverty — seems to be a significant confounder in the previous association. The underlying rationale stems from how income inequality is associated with various deleterious life events that come with it, impacting individuals’ overall mental health. In Pickett and Wilkinson’s (2015) systematic review, the association between social class, psychosis, and violence seems to be firmly and causally related. Similar results were reported, in which people with mental illnesses, including SSD and those living in poverty are at a significantly higher risk of experiencing both victimisation and propensity to commit violent acts due to a cycle of suspicion and mistrust (Hiday, 1997; Choe et al., 2008). However, Fusar-Poli et al.’s (2022) review criticised previously established associations, as these studies employed generally small sample sizes and the high heterogeneity between studies, and therefore, risks further stigmatising those with SSD living in poverty. Additionally, a comparative cross-sectional Ethiopian review on the subject found that SSD individuals living in extreme poverty are at a higher risk of being victimised as opposed to perpetrating violence (Tsigebrhan et al., 2014).

In sum, the relationship between SSD and violence is a complex one. Despite various efforts to better understand its causal mechanisms, these results should be critically scrutinised regarding sample sizes, heterogeneity, and methodologies to avoid further stigmatising individuals with SSD.

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