Cannabis is now three times more toxic than it was ten years ago.

Scientific discussions about the true risks of cannabis have flourished in recent years , thanks to more open regulation that has allowed for much more comprehensive and reliable studies . All of this occurs in a very specific context: the ongoing race, especially on the black market, to cultivate varieties with ever-increasing concentrations of psychoactive compounds.

Marijuana contains a wide range of active ingredients, but the most important one, and the one that most concerns experts, is tetrahydrocannabinol, or THC . Although there is evidence that in very specific cases it may have some therapeutic potential, it has also been associated with a certain risk of cardiovascular problems, abuse disorders, and even psychotic episodes and cognitive impairment.

"Consumption is more dangerous than it was 20 years ago"

Well, as a study published in the academic journal Missouri Medicine and cited by the scientific news agency SINC shows, the concentration of THC in black market marijuana has only grown exponentially in recent decades . So much so that, while before the 1990s it was around 1 or 2%, today there are varieties that reach 35%.

More specifically, Fernando Berrendero, a researcher from the Faculty of Experimental Sciences at Francisco Vitoria University and director of the Neurobiology of Addictive and Anxiety Disorders Research Group, mentions that in the last decade, the amount of THC present in Cannabis sativa varieties (the plant's scientific name) has tripled. "This means that its consumption is more dangerous than it was 20 or 30 years ago ," he says. And this, he believes, may have led to the social perception of the risk involved in using the substance not corresponding to reality.

"The risks increase depending on age, dose (or amount of THC), and the duration of abuse... whether continuous or not," Marina Díaz Marsá, president of the Spanish Society of Psychiatry and Mental Health, reminds SINC. In any case, she emphasizes that "it multiplies by nine the chances of developing any psychiatric disorder, be it bipolar disorder, schizophrenia, depression, anxiety, or suicidal behavior." For his part, psychiatrist Celso Arango, former president of the Spanish Society of Psychiatry and Mental Health and director of the Institute of Psychiatry and Mental Health at Gregorio Marañón Hospital, warns that "in the case of schizophrenia, the risk triples."

"No one has 0% risk"

This expert goes further, emphatically stating that "if cannabis didn't exist, the number of schizophrenia cases would be drastically reduced," according to evidence gathered in longitudinal studies that also took into account other variables, such as genetics or the experience of traumatic events. In the Adolescent Psychiatry Unit at Gregorio Marañón University Hospital, he comments, "almost 50% of patients who arrive with psychotic episodes test positive for cannabis."

Smoking cannabis doubles the risk of dying from a heart attack or stroke.

The reality is worrying, especially considering the trend toward regulating the substance, which is increasing its accessibility in some parts of the world. For example, Díaz Marsá says that in Canada, since the substance was legalized, admissions for psychotic episodes have tripled.

This danger doesn't affect everyone equally. Although Arango warns that no one is at 0% risk, he also explains that the danger increases exponentially when the user has a genetic predisposition or lives with chronic stress. "If, on top of that, you have a genetic predisposition to schizophrenia (something that occurs in 1% of the population), cannabis is poison."

"Smoking cannabis causes schizophrenia"

"In very vulnerable people, smoking a single joint can trigger psychosis. What smoking does is awaken the mental illness that's in one's genes," Díaz Marsá agrees. "And no one knows who is vulnerable. It's like Russian roulette."

Recently, a team of researchers from the Neuropsychopharmacology group at the University of the Basque Country (UPV/EHU) has detected "potential biomarkers in blood that could help predict the risk of some people developing a psychiatric illness such as schizophrenia if they consume cannabis," according to lead researcher Leyre Urigüen, as published in the scientific journalScientific Reports . This is an advance that could help identify those most at risk, potentially helping to prevent a significant percentage of cases of this terrible disease.

In addition to the increased likelihood of suffering psychotic episodes , cannabis can have effects on aspects such as memory and cognitive abilities, which, according to these experts, can be permanent in some cases (especially when consumption begins at an early age).

For all these reasons, Marina Díaz concludes: "Smoking cannabis causes schizophrenia and seriously impairs your life plan. It causes cognitive impairment, especially if you smoke before the age of 21."

References

Elizabeth Stuyt. The Problem with the Current High Potency THC Marijuana from the Perspective of an Addiction Psychiatrist. Missouri Medicine (2025). PMID: 30643324; PMCID: PMC6312155.

Laura G. de Rivera. The cannabis smoked today is three times more toxic than a decade ago. SINC (2025). Accessed online at https://www.agenciasinc.es/Reportajes/El-cannabis-que-se-fuma-hoy-es-tres-veces-mas-toxico-que-hace-una-decada on July 18, 2025.

Villate, A., Olivares, M., Usobiaga, A. et al. Uncovering metabolic dysregulation in schizophrenia and cannabis use disorder through untargeted plasma lipidomics. Scientific Reports (2024). DOI: https://doi.org/10.1038/s41598-024-83288-5

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