BIn young men, up to 30 percent of all schizophrenia cases can be traced back to problematic cannabis use. Scientists write this in the journal Psychological Medicine. They had looked at a huge data set from Denmark, such as so-called cannabis use disorders (CUD) and schizophrenia related. CUD criteria include heavy use, strong craving for the drug, or giving up or limiting important social, work, or leisure activities.
Previous studies had already shown that cannabis use disorders can be associated with serious mental illnesses, such as schizophrenia – this applies to men as well as women. Now researchers around Carsten Hjorthøj from the Copenhagen University Hospital examines who is at greatest risk.
The analysis shows that 15 percent of all male schizophrenia in Denmark in 2021 could have been avoided without cannabis use disorders (CUS). For women it was four percent. The proportion was particularly high at up to 30 percent among younger men aged 21 to 30. 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. Around 45,300 of these people had been diagnosed with schizophrenia. The researchers then looked at which individuals in each gender and age group also had known cannabis use disorders and then estimated the proportion of all schizophrenia cases associated with such a disorder.
The researchers also point out that the number of people with a cannabis use disorder has generally increased over the years and that the THC content in cannabis products is also increasing. In Denmark, an average of 13 percent was measured in 2006, and in 2016 the THC content was 30 percent.
A man builds a joint.
Source: dpa
Their representative, nationwide study extends the finding of a 2019 case-control study by Marta Di Forti and her team. At that time it was found that in cities where cannabis products with a particularly high THC content are regularly consumed, the number of psychotic illnesses is also particularly high. Eleven European cities were examined at the time, with Amsterdam and London taking the top spots. Consequently, the strength of the cannabis consumed could also be relevant to the risk of schizophrenia, the researchers believe.
The medical director of German Center for Addiction Issues in Children and Adolescents (DZSKJ) am University Hospital Eppendorf (UKE) in Hamburg, Rainer Thomasius, refers to another aspect of the study: “It is really shocking that, according to the analysis, the proportion of new cases of schizophrenia that can be attributed to a cannabis use disorder has increased continuously over the past five decades. “
Study is transferrable to Germany
In many cases, this is the beginning of a long ordeal for those affected: “Schizophrenia is one of the most serious psychiatric illnesses because it is associated with a severely reduced quality of life, a high need for treatment, dependency and a severe restriction of social participation,” explains Thomasius. The study from Denmark can also be transferred to Germany.
The German federal government plans to legalize cannabis. Thomasius and other experts suspect that consumption will increase overall in this country. “As a result of this increase, more people will develop cannabis use disorders and the number of people suffering from schizophrenia will increase. The incidence of cannabis-induced depressive disorders and anxiety disorders will also increase,” predicts child and adolescent psychiatrist Thomasius.
Study co-author Nora Volkow warns in a press release: “As access to potent cannabis products continues to increase, it is critical that we also expand prevention, screening and treatment for people who experience mental illness associated with cannabis use could.”
First author Hjorthøj sees another fundamental problem: “The increasing legalization of cannabis in recent decades has resulted in it becoming one of the most commonly consumed psychoactive substances in the world, while at the same time the public perception of the harmfulness of cannabis has decreased.”
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