Chapter 11

Understanding and assessing substance use in schizophrenia

The use of substances, be they licit or illicit, is regrettably very common amongst people with schizophrenia. The approach of clinicians needs to encompass a high degree of awareness, but to engage the individual in a non-judgemental and supportive manner. This chapter outlines the size of the problem, the impact on illness course, and the assessment of substance use comorbidity in schizophrenia. Treatment approaches are covered in Chapter 12.

The size of the problem

Use of substances of abuse by people with schizophrenia is very common. The population-based ECA study from the US (Regier et al. 1990) reported a lifetime rate of problematic substance use in 47% of respondents with schizophrenia, compared to 16% of the general population. Using a different design, the Australian Survey of High Impact Psychoses (SHIP) assessed substance use rates amongst 1,825 people with psychotic disorders and documented past year rates of 49% for cannabis abuse/dependence, 32% for stimulants, and 27% for other illicit drugs; daily alcohol use was reported by 25% of respondents (Moore et al. 2012).

In a review of the international literature, Cantor-Graae and colleagues (2001) suggested a mean prevalence rate of around 40–60% for any substance of abuse/dependence (excluding caffeine and nicotine) amongst people with schizophrenia. Of course, rates do differ to some extent across jurisdictions and the pattern of drugs used varies dependent upon availability, cost, and legislation. Box 11.1 shows the range of reported rates. Tobacco is consistently the most widely used drug, whilst cannabis is uniformly the most common ‘illicit’ drug (note it is legal in some jurisdictions), with amphetamines (mostly as crystal methamphetamine) second in much of South East Asia and Australasia; in the US, cocaine is second. We address each of these most prevalent drugs in turn. Note we exclude caffeine, but acknowledge very high rates of use amongst people with schizophrenia.

Theories as to why there are such high smoking rates amongst people with schizophrenia include social affiliation and oral gratification, as well as neurobiological reward and amelioration of withdrawal effects. For a full discussion of smoking and schizophrenia the reader is referred to Chapter 5 of the companion volume in this series, Physical Health and Schizophrenia (Castle et al. 2017).

Alcohol

Alcohol is a socially sanctioned drug in most parts of the world. It is also strongly advertised and freely available at many social events. Given the social exclusion of many people with schizophrenia and the high rates of social anxiety (see Chapter 7), use of alcohol is common amongst this group. The medical, psychiatric, and psychosocial impacts of alcohol abuse are well described (see Box 11.2). People with schizophrenia are arguably at particular risk for a number of these adverse outcomes and it is also recognized that their overall physical health is generally poor and their healthcare suboptimal. Thus, alcohol can be an important added risk factor for early death. There are also implications of alcohol use in people on prescribed psychotropic drugs, as side effects may be exacerbated.

Cannabis use amongst people with schizophrenia has come under particular scrutiny over the last decade, in part because cannabis is becoming more and more potent in terms of its psychotomimetic properties. Thus, the proportion of the main psychotomimetic chemical in the cannabis plant, delta -9-tetrahydrocannabinol, is much higher in modern strains of the plant product, whilst the level of cannabidiol (CBD), which has potential antipsychotic effects, has reduced. The impact of this has been shown in studies that have demonstrated more detrimental impact of high-potency cannabis (known as ‘skunk’) in people with schizophrenia (Di Forti et al. 2009). Also, legalization (or at least decriminalization) of cannabis in many jurisdictions, as well as the promotion of medicinal cannabis have led to renewed interest in the compound.

The psychiatric and neuropsychiatric effects of cannabis are well described (Box 11.3). It is fair to say that most of these effects are relatively mild compared to many other drugs, and some of the associations are largely due to reverse causality: for example, most of the association with depression is explicable by use of cannabis by people who already have depression, rather than cannabis being the causal factor for the depression. Having said this, there is particular concern about its impact on people with an underlying vulnerability to mental instability, not least those with schizophrenia. Thus, it is well described that cannabis can worsen the course of established schizophrenia and also that it can ‘bring forward’ the onset of the illness. The latter has particular implications for young people, as an earlier onset of schizophrenia results in loss of the opportunity to attain key developmental milestones (educational and social) and this in turn has negative implications for long-term functional recovery.

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Generalized anxiety and panic disorder in schizophrenia Personality disorders and schizophrenia Social anxiety disorder and schizophrenia Post-traumatic stress disorder and schizophrenia Schizophrenia and obsessive compulsive disorder Why are psychiatric comorbidities so common in schizophrenia and why are they so often missed in clinical practice?

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