South African study links cannabis use with more severe psychosis and higher relapse risk

Nearly half of people admitted with schizophrenia spectrum and other psychotic disorders in a South African study were current cannabis users, and researchers say that cannabis use is linked to a more difficult course of illness. The study, published in the South African Journal of Psychiatry, examined clinical records of patients admitted to a psychiatric hospital and found associations between cannabis use and earlier onset, greater symptom severity and higher relapse.

Study sample and key numbers

The researchers reviewed 370 clinical records of patients aged 13 and older who were admitted to a psychiatric hospital between June 2018 and June 2020. They reported that 48.9% of patients were current cannabis users and 51.1% had used cannabis at some point in their lives.

The study population was predominantly young and male: 66.2% were aged 16 to 34 and 70.5% were male. Additional demographic findings included 93.9% unmarried, 88% with grade-school level education and 89.2% unemployed. The median duration of psychotic illness was three years, and 48% had been admitted to hospital three or more times.

How cannabis use related to illness course

The authors warned that cannabis use alongside a psychotic disorder can be associated with a more difficult recovery. As they put it:

“Comorbid cannabis use in schizophrenia spectrum and other psychotic disorders is associated with a more severe course of illness.”

They said people with psychotic disorders who use cannabis can develop symptoms at a younger age and may experience more severe symptoms than non-users. The researchers also reported that cannabis users with psychosis may have challenges with taking psychiatric medication consistently.

In the study’s words:

“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.”

Broader social and clinical consequences

The researchers noted that the impact of comorbid cannabis use can extend beyond medical symptoms to affect relationships, employment and daily functioning. They wrote that consequences documented in the literature include homelessness, violence, incarceration and an increased burden of care for families. As they stated:

“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.”

Complex relationship between cannabis and psychosis

The authors emphasised that the relationship between cannabis and psychosis is complicated. They noted that while cannabis use can increase the risk of developing psychosis, people experiencing early symptoms may also use cannabis, stating:

“Psychosis and prodromal schizophrenia symptoms may also exacerbate cannabis use.”

The study also highlighted concerns about high-potency cannabis and cited recent research indicating increased risk:

“Recent studies show that the use of high potency cannabis increases the risk of FEP and subsequent schizophrenia.”

Context in South Africa

The researchers pointed out that cannabis use among people with psychotic disorders has been reported at particularly high levels in South Africa in earlier studies, with previously reported prevalence ranging from 37% to 68% depending on the population and setting. They cited two prior regional findings: 68.8% prevalence among adolescents with psychotic disorders in KwaZulu‑Natal and 35% prevalence among adults in another study.

The authors noted these earlier studies were conducted about a decade earlier and before the decriminalisation of personal cannabis use in South Africa. They wrote that cultural, environmental and legislative factors may influence patterns of use in the African setting.

Implications for families and clinical care

The study authors urged that cannabis use should be identified and considered when a person with psychosis is receiving psychiatric treatment. They said the combination of cannabis use and psychotic illness can complicate treatment and recovery, and highlighted a high prevalence of comorbid cannabis use among people with psychotic disorders in the literature.

As the researchers summarised:

“The literature suggests a high prevalence of comorbid cannabis use among people with psychotic disorders.”