Is hashish still around

Hemp side effects study : Those who use cannabis on a daily basis are more likely to develop psychoses

The dispute has been going on for a long time: some point to studies that establish a connection between increased cannabis consumption and new cases of psychosis. Therefore, cannabis should not be legalized. Others say: people who are mentally ill or will become ill anyway, simply resort to drugs like cannabis more often.

The trigger or even the cause of the psychosis or other mental illnesses (such as depression) is therefore not the substance and legalization could therefore not lead to a glut of psychotic people. This is contradicted by a careful study carried out in over 2000 test subjects and eleven locations in Europe under the direction of Marta Di Forti, from the Institute for Psychiatry, Psychology and Neuroscience at King's College in London, published in the journal "Lancet Psychiatry".

The more cannabis, the more confused the psyche

Admittedly, this investigation cannot produce any clear evidence that cannabis is the cause of psychosis. But it shows that where cannabis is freely available, more people develop psychosis. Five out of ten such psychosis cases in Amsterdam are related to frequent, daily cannabis use, in London it is three out of ten.

In addition, those in the study who added cannabis to their bodies on a daily basis were three times more likely to develop psychosis than non-users. Among those who preferred a substance with a particularly high THC content (the active ingredient tetrahydrocannabinol), the researchers even counted five times more psychotic attacks in the study phase.

"Consistent with previous studies, our results show that using cannabis with high THC concentrations has a more damaging effect on mental health than using less concentrated cannabis," says Di Forti. "They also point out for the first time how cannabis consumption influences the frequency of new mental illnesses in the population." In the course of legalization initiatives in various countries, it is of particular importance for public health to also take into account the possible side effects of daily hemp consumption.

If cannabis were not available, the rate of psychosis would drop by half

At the eleven locations in England, the Netherlands, France, Spain and Italy (as well as one location in Brazil), the researchers first determined the number of people newly diagnosed with psychosis between 2010 and 2015 and asked them to participate in the study. 901 agreed, as did 1237 healthy volunteers from the eleven regions. In addition to other health-related information, they all gave information about their consumption behavior regarding cannabis and other drugs, also regarding the "strength" of the substance.

It turned out that the group of psychotics consumed cannabis significantly more daily (244 of 901, 29 percent) than in the group of healthy people (84 of 1237, 7 percent). Among the psychosis patients there were 334 (37 percent) who preferred particularly strong substances, among the healthy it was only 19 percent (240).

Other factors that can also trigger or promote psychosis were also taken into account in the study - such as other drugs such as alcohol, tobacco or cocaine, but also educational and employment status. However, this did not detract from the connection between cannabis and psychosis, which has already been found in many other studies.

However, it remains unclear to what extent the genetic predisposition of the study participants or other previous psychological illnesses that were not asked about contribute to the risk of psychosis, says Dieter Meyerhoff from the University of California in San Francisco, and also whether the test subjects had started using cannabis before they developed psychosis. "There is still the possibility of the alternative explanation that participants with first-time psychoses use more cannabis - instead of the other way around, as the authors justify plausibly and convincingly."

The study is reason enough to consider the possible consequences before legalizing cannabis. "Unfortunately, today as a society we still know far too little about the long-term health consequences of uncontrolled cannabis use, especially among teenagers and young adults." Society has to be very careful. "Let us take the opportunity to study the relevant developments in the countries that have already legalized cannabis before we uncritically follow them."

In Amsterdam, for example, Di Forti and colleagues conclude from their data, the rate of new cases of psychosis would fall by half, from around 38 cases per 100,000 inhabitants to 19 cases if cannabis were no longer available. In London there would be only 32 cases of psychosis per year instead of 46.

Consumption is also increasing in Germany

Cannabis is not yet legally available in Germany, but it is still consumed in this country. Therefore, the results of the study can also be transferred to Germany, says Rainer Thomasius, Medical Director of the German Center for Addiction Issues in Children and Adolescents at the Hamburg University Clinic in Eppendorf. According to the 2018 Drug and Addiction Report, the THC content in cannabis products is also in Germany has risen sharply in recent years.

"In the US states that legalized cannabis, the average THC level continued to rise as a result of legalization." Some cannabis products with a 40 to 50 percent THC content are available there, says Thomasius. "It is to be feared that the legalization of cannabis will lead to a significant increase in the risk of developing psychoses." (with smc)

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