A recent study published in The American Journal of Psychiatry by researchers at Johns Hopkins University has brought to light a reality that many young people and their families prefer to ignore: cannabis use during adolescence triples the risk of developing mental disorders compared to alcohol or other drug use. The research, disseminated by the Spanish Society of Dual Pathology (SEPD), analyzed both adolescent and adult populations, but the most striking impact was observed among those under 17.
Dr. Néstor Szerman, president of the Dual Pathology Foundation and psychiatrist at the Gregorio Marañón Hospital in Madrid, has been unequivocal on the matter: cannabis is the drug with the most psychoactive properties , far exceeding many other commonly used substances. According to Szerman, the social perception that it is a soft drug or a natural product free of dangers is not supported by previous scientific data, nor by the findings of this new research.
A particularly vulnerable adolescent brain
The human brain undergoes a neurodevelopmental process that doesn't finish until well into the 20s. During this stage, the circuits responsible for impulse control mature more slowly than those linked to reward , leaving adolescents more vulnerable to the effects of cannabis. Szerman explains that this imbalance in the rate of brain maturation makes young people more prone to cannabis use and suffering its consequences.
The Johns Hopkins study confirms that the impact of cannabis is particularly pronounced in this age group. While the effects of cannabis are less pronounced in adults, the risk of developing a mental disorder associated with its use skyrockets in adolescents. Scientific evidence accumulated in recent years reinforces this conclusion , and experts warn that this is not a minor problem.
Genetic vulnerability and risk of psychosis
Not all teenagers who use cannabis face the same risks. Research indicates that those with a shared genetic predisposition to both addiction and other psychiatric disorders are the most vulnerable. The risk of schizophrenia increases by 52% among teenagers with cannabis use disorder , while the risk of depression increases by 30%. These figures, drawn from the study, highlight the close relationship between cannabis and mental health.
Szerman explains that adolescents with low genetic vulnerability can develop psychotic episodes when consuming cannabis with high THC content, the main psychoactive component. Conversely, when vulnerability is high, even cannabis with a low percentage of THC can trigger a psychotic episode , which in almost half of the cases progresses to a chronic psychotic disorder. This finding is especially concerning because many young people are consuming varieties with increasingly higher concentrations of THC without being aware of the danger.
The relationship between cannabis and psychosis
The link between cannabis use and psychosis is not new, but it is increasingly supported by scientific evidence. A study published in JAMA Psychiatry just over a year ago, based on brain imaging techniques, found that people with cannabis use disorder have higher levels of dopamine in the same brain region associated with psychosis . This alteration can interfere with normal brain processes and increase the risk of psychosis, especially in individuals who are already vulnerable.
As an example of this relationship, Szerman cites the case of the province of Ontario, Canada, where the legalization of cannabis has been accompanied by a threefold increase in the incidence of psychotic episodes . The expert also points out that the human brain has an endogenous endocannabinoid system, which doesn't exist for the purpose of cannabis use, but is linked to survival. When this system is dysfunctional due to genetic or acquired causes, it can lead to mental disorders such as cannabis addiction and psychosis.
Dual pathology: the challenge of comprehensive treatment
In the most vulnerable individuals, dual diagnosis—the coexistence of an addiction and another mental disorder—is the norm. According to the study's data, people with ADHD who use cannabis have an eight times greater risk of developing an addiction to this substance , figures similar to those observed in other major affective disorders such as depression. Furthermore, approximately 35% of patients with chronic psychosis, such as schizophrenia, also present with a cannabis use disorder.
Szerman insists that any patient with cannabis addiction should always have other associated mental health disorders identified in order to guide treatment appropriately. The approach must be comprehensive and integrated , addressing all mental health disorders together. However, the expert laments that many patients and their families continue to suffer from the so-called "wrong door syndrome," whereby they receive treatment for the addiction or for the other mental health disorder, but almost never receive combined treatment, which hinders recovery and increases the risk of relapse.
The data from this research reinforces the need to dismantle the idea that cannabis is a harmless drug, especially among adolescents. At a stage when the brain is still maturing, minimizing its risks can have consequences that affect young people for the rest of their lives . The scientific evidence is clear: cannabis use in adolescence not only triples the risk of mental disorders, but, in combination with genetic vulnerability, can trigger serious illnesses such as schizophrenia or depression. Experts are calling for greater public awareness and a healthcare approach that treats addiction and psychiatric disorders together, to prevent young people from falling into a vicious cycle from which it is difficult to escape.
