Illicit substance use is a worldwide problem and contributes significantly to the global burden of disease.¹ The United Nations office on Drugs and Crime world drug report (2020) found that cannabis is one of the most commonly used drugs, with approximately 192 million users, of whom 35 million meet the criteria for cannabis use disorder.²

Schizophrenia is a chronic and severe mental illness that is characterised by positive, negative, affective and cognitive symptoms. It runs an often-disabling course and places a considerable burden on patients, their families, the healthcare system and society at large.^3,4 Comorbid cannabis use in schizophrenia spectrum and other psychotic disorders is associated with a more severe course of illness. Cannabis users with psychosis have an earlier onset of illness, increased symptom severity, poorer adherence to psychiatric medication, poorer functional outcomes, higher relapse rates and longer hospital stays compared with non-users.^{5,6,7,8,9,10,11} In addition, people with schizophrenia spectrum and other psychotic disorders and comorbid cannabis use tend to have poorer psychosocial functioning, homelessness, violence, incarceration and increased burden of care for families.^4,12,13,14

The literature suggests a high prevalence of comorbid cannabis use among people with psychotic disorders,^15,16 with the concurrent use of other substances, for example alcohol, also having been reported.¹⁰ In a meta-analysis of 35 studies of adults presenting with first episode psychosis (FEP), 33.7% reported cannabis use, 30.7% of outpatients with FEP reported past month cannabis use and 34.7% met the criteria for lifetime cannabis abuse or dependence.¹⁷ Studies conducted in the United States of America (USA) and Canada found that cannabis use is twice as common in patients with severe mental illness, such as schizophrenia, compared to the general population.¹⁸ The prevalence of cannabis use in South African populations with psychotic illness has seen reported to be between 37% and 68%, depending on the setting and population.^19,20,21 A Cape Town study found the most common substance use disorder associated with psychosis was cannabis use disorder, with a prevalence of 34.3%.¹⁵

Recent studies show that the use of high potency cannabis increases the risk of FEP and subsequent schizophrenia, and that psychosis and prodromal schizophrenia symptoms may also exacerbate cannabis use.²² Genetics and environmental factors play a role in this bidirectional relationship between psychosis and cannabis use.²³ Various socio-demographic and clinical factors may be associated with cannabis use among people living with psychosis. International studies found that cannabis use in patients with psychosis was predominantly in males, younger in age, of a low education level and socio-economic status.^24,25 Data from South Africa (SA) and other African countries have shown similar findings, with unemployment, being single, an inpatient status, and recurrent admissions being additional factors associated with cannabis use.^{5,15,16,19,26,27}

Hence we note a high comorbidity between cannabis use and psychosis, and that the dual diagnosis of a cannabis use and psychotic disorder is a poor prognostic factor. A study conducted in India had similar findings where cannabis use had a high prevalence for psychotic disorder and this co-occurrence is a poor prognostic factor.²⁸ In KwaZulu-Natal (KZN) Province, SA, Paruk et al.²⁰ found a cannabis use prevalence rate of 68.8% in the adolescent psychotic population, while Burns and colleagues found a prevalence rate of 35% in the adult population of the same province.²⁹ These studies were all conducted about a decade ago, before the personal use of cannabis was decriminalised in SA.³⁰ The factors associated with comorbidity in the African setting may also differ from elsewhere, as this may be influenced by cultural and environmental differences between countries and availability of cannabis, while the decriminalisation and legalisation policies on cannabis may have an impact on the patterns of use.

This research aimed to describe the socio-demographic and clinical profiles of patients admitted with schizophrenia spectrum and other psychotic disorders to a psychiatric hospital. The study also aimed to determine the prevalence and pattern of cannabis use (current vs. lifetime) in this population and to describe any associations between cannabis use and socio-demographic and clinical variables.

The association between cannabis use and psychosis has been established in recent years, but there has been a move to decriminalise personal cannabis use globally and in SA; hence the authors aimed to review the prevalence of current and lifetime cannabis use in people living with psychosis.

A retrospective chart review was conducted at a tertiary psychiatric hospital that offers psychiatric services in the eThekwini District, KZN Province, SA.

The main findings of this study were the high prevalence of current (48.9%) and lifetime (51.1%) cannabis use among people with schizophrenia spectrum and other psychotic disorders, and that being male, of younger age and current alcohol use were associated with ongoing cannabis use.

Our study showed that CCU in psychosis is high at 48.9% but slightly lower compared with a study conducted in the Eastern Cape Province of SA, which showed a prevalence of 59.8%.¹⁹ This difference may have been attributed to the Eastern Cape cohort being individuals with FEP only. Temmingh and Mall, in their Western Cape cohort, reported a lower prevalence of 34.3%, which may be because of their assessing for substance use disorder rather than cannabis use.¹⁵ In the Western Cape Province (SA), 57% of adolescents presenting with FEP were reported to be cannabis users.²¹

Paruk et al.²⁰ reported the prevalence of cannabis use at 68.8% in adolescents with FEP in KZN, while Burns et al.³⁶ reported 35% prevalence of comorbid cannabis use in their adult FEP sample. This study was also conducted in KZN but included patients 16–45 years of age, and it is possible that patients may be less likely to continue cannabis use with advancing age, as was evident in our study, where those 45 years and older had lower odds of cannabis use compared with the 16–34 years age group. This could be related to peer pressure and stress or negative life events experienced by younger people with psychosis.³⁷ The literature also suggests that cannabis exposure during the adolescence period, a critical time in neurodevelopment, may have lasting adverse effects that predispose to the development of psychosis as the individual grows older, even when they are no longer using cannabis^38,39,40; hence the finding of increased use in younger people is a concern and we need to ensure that young people at risk of or presenting with psychosis receive psychoeducation and care for comorbid substance use.

Similar to our findings, other studies have also consistently reported cannabis users in populations with psychosis to be predominantly male, of young age, having a low level of education and unemployed.^{5,15,16,19,24,25,26} In a USA community hospital cohort, the findings were that being male, young, unemployed and homeless was significantly associated with cannabis use in patients with schizophrenia spectrum disorders.⁴¹ A study conducted in Spain in patients with FEP also found users to be predominantly male who started cannabis use earlier in life.⁴² A study conducted in Morocco also reported patients diagnosed with schizophrenia who were using cannabis were young, male, presented earlier in life and had poor adherence to medication.⁴³ Local findings have also been consistent, with cannabis users being more likely to be young and male.^5,19 The vulnerability of young males suggests the need for earlier public health programmes on substance use among this cohort who may be at risk of psychosis to improve outcomes.

Our study found that 52.8% of current cannabis users were also using alcohol, which is consistent with an international study conducted in Canada, where people with psychosis were likely to have an alcohol and cannabis use disorders at 21% and 27%, respectively. Rates of substance use were highest in the first five years of psychotic illness at 20% – 33% for alcohol and 21% – 45% for cannabis. Alcohol use was associated with higher social functioning and less negative symptoms,¹⁰ this being similar in a study conducted in the Eastern Cape, SA; which found that patients with FEP used cannabis followed by alcohol use.¹⁹ This is also supported by a study conducted in the USA, which found that patients with schizophrenia spectrum disorders and cannabis use were more likely to use other substances, such as alcohol, tobacco and cocaine.⁴¹ It suggests the need to screen those with psychosis for polysubstance use and reinforces the call for the much-needed dual diagnosis units that cater to substance use rehabilitation and psychosis, which are not available in KZN, SA.

The finding that almost 50% of our study population had more than three or more admissions was also concerning. While on logistic regression this study did not find any associations between cannabis use and re-hospitalisation, suggesting that the findings were compounded by other factors such as poorer access to healthcare in the province where patients were possibly not admitted to hospital and managed in the community. This finding is, however, contrary to findings in the literature where studies have consistently found that schizophrenia and continued cannabis use leads to poorer outcomes, such as a more complicated course of illness, as evidenced by frequent relapses, shorter periods of time between relapses, longer hospitalisations and more intensive psychiatric care.^5,11,19,27 This is also consistent with both local as well as other international literature.^27,44,45 As the literature shows that discontinuing cannabis use has improved outcomes, it becomes essential that we review the modifiable factors associated with psychosis outcome.¹¹

There was a lack of association between the clinical variable HIV infection with cannabis use in people with psychosis in this study, which is consistent with another local study, but inconsistent with international research.^46,47,48 This may be because of almost 30% of participants not having a documented HIV result, which may be attributed to poor record keeping, limited HIV testing access or the inability to provide consent, which may have affected the finding. Substance use and psychosis may increase risky sexual behaviour and hence HIV risk^49,50,51; therefore, the association between HIV and cannabis use in those living with psychosis needs to be explored further.

The high rates of cannabis use, with almost half the people in the study with psychosis still reporting current use, is an important public health concern. Cannabis use was associated with a vulnerable group of young males with lower education and comorbid alcohol use, and with over 50% having more than three or more admissions; the data suggest that its continuous use leads to a poorer prognosis. The findings highlight the need to review treatment programmes offered at psychiatry units, with an urgent need for dual diagnosis programme that addresses substance use in people living with psychosis in a comprehensive and integrated manner.

Further longitudinal studies are required to better understand association between ongoing cannabis use and psychosis outcomes, including intervention studies. Clinically we need to address cannabis use with a more concerted effort and to develop dual diagnosis units to address comorbid substance use.