Borderline-Selbsthilfe

High cannabis use is associated with certain mental illnesses. Using the example of schizophrenia, researchers are now showing how significantly the risk can increase as a result of heavy smoking.

Copenhagen - In young men, up to 30 percent of all cases of schizophrenia are likely to be linked to problematic cannabis use. This is what researchers write in the journal Psychological Medicine.

They had examined the connection between so-called Cannabis Use Disorders (CUD) and schizophrenia in a large data set from Denmark. Criteria for a cannabis use disorder include heavy use, a strong craving for the drug, or giving up or reducing important social, work, or leisure activities.

It was already known from previous studies that cannabis use disorders can be associated with serious mental illnesses, such as schizophrenia - in both men and women. Researchers led by Carsten Hjorthøj from Copenhagen University Hospital have now investigated who is at greatest risk.

Cannabis use disorders can cause schizophrenia

The analysis shows that without cannabis use disorders (CUS) in 2021, 15 percent of all male schizophrenia in Denmark could have been avoided. For women, it was four percent. In younger men aged 21 to 30, the proportion was particularly high at up to 30 percent. The researchers conclude that CUS is an important risk factor for schizophrenia.

They had collected data from more than 6.9 million men and women from Danish health registries. About 45,300 of these people had been diagnosed with schizophrenia. The scientists then examined which people in the various gender and age groups were also known to have cannabis use disorders. They then estimated the proportion of all schizophrenia cases that were associated with such a disorder.

The number of people with cannabis use disorders has generally increased over the years, and the THC content of cannabis products has also increased, the researchers said. In Denmark, an average THC content of 13 percent was measured in 2006, in 2016 it was 30 percent.

Rising proportion of new cases

Their representative, nationwide study extends the findings of a 2019 case-control study conducted by Marta Di Forti and her team. At the time, it was found that the number of psychotic illnesses was particularly high in cities where cannabis products with a particularly high THC content were regularly consumed. Eleven European cities were the subject of the study at the time, with Amsterdam and London leading the way. According to the researchers, the strength of the cannabis consumed could also be relevant to the risk of schizophrenia.

Rainer Thomasius, Medical Director of the German Center for Addiction Issues in Children and Adolescents (DZSKJ) at the University Hospital Eppendorf (UKE) in Hamburg, points out another aspect of this study: "It is alarming that, according to this analysis, the number of new schizophrenic diseases, attributable to a cannabis disorder has steadily increased over the past five decades”.

Schizophrenia is one of the most serious psychiatric diseases because it is associated with a high need for care, dependency and severe restrictions on social participation," explains Thomasius. The Danish study can also be transferred to Germany.

Harmfulness is underestimated

Cannabis is to be legalized according to plans by the federal government. Thomasius and other experts suspect that consumption in this country will increase overall. “As a result, more people will develop a cannabis use disorder and the number of schizophrenic patients will increase. The incidence of cannabis-induced depressive disorders and anxiety disorders will also increase,” according to the prognosis of the child and adolescent psychiatrist Thomasius.

Co-author Nora Volkow warns in a press release: "As access to potent cannabis products continues to increase, it is vital that we also scale up prevention, early detection and treatment for people who may develop mental disorders associated with cannabis use.

The legalization of cannabis over the last few decades has ensured that it is now one of the most consumed psychoactive substances in the world.