According to new research, individuals who consume cannabis on a daily basis and those who use cannabis with high levels of tetrahydrocannabinol (THC) may be thrice more likely to develop psychotic disorders compared to those who have never used the drug.
THC is the main psychoactive ingredient of cannabis and is responsible for giving users the high and the mind-altering effects. This is why cannabis products with high THC content is more associated with the recreational use of the drug.
The study, published in the journal the Lancet Psychiatry on Tuesday, presents evidence that is consistent with previous studies in suggesting that high-potency cannabis and the heavy use of the drug can be harmful to the mental health of users. A cannabis product is considered to have high potency if it contains at least a 10% concentration of THC.
How the study was conducted
Dr. Marta Di Forti, a clinician scientist at the Institute of Psychiatry, Psychology, & Neuroscience in King’s College London, and the lead author of the study, explained that in studying psychotic disorder, they are talking about people who meet the diagnostic criteria for psychosis and who come to mental health services for treatment. She said that these patients have to have symptoms of the condition across the spectrum, including hallucination and delusion, that lasted for a week or more.
Dr. Di Forti and her team looked at data from 11 sites in five European countries — the UK, France, the Netherlands, Italy, and Spain — as well as one site in Brazil, in order to understand whether there is a connection between cannabis use and psychosis. The study involved 901 patients who experienced a first-time episode of psychosis over a period of five years. The researchers compared data from these patients with data from 1,237 matched non-patients.
The study found that daily cannabis use was more common among patients diagnosed with psychosis compared to those in the control group. About 30% of these patients reported using cannabis every day compared to only 7% of non-patient controls.
Moreover, it was found that the use of high-potency cannabis was more common among patients, at 37%, than among the controls, at 19%.
Overall, the researchers estimated that those who used cannabis daily were three times more likely to experience a first episode psychosis than those who never used the drug. This likelihood increased to five times more likely for individuals who use high-potency cannabis on a daily basis.
No clear explanation for results
According to Dr. Di Forti, high-potency weed contributes to the incidence of psychosis but there is no complete explanation for it. She noted that only some users develop a psychotic disorder and that it is unclear why not all cannabis users are equally susceptible.
Nevertheless, she said that the new study may be helpful with regard to medical cannabis considering that some of the products may include small levels of THC. For instance, maybe psychotic disorder should be listed as among the potential side effects of using the drug.
And while the results of the study do not provide enough information for the authors to be able to indicate a specific amount of cannabis or THC that is safe, they estimated that one in five new cases of psychosis may be connected to daily cannabis use and that one in 10 cases may be linked to the use of high-potency weed.
Dr. Di Forti said that with the changing legality of cannabis, it is a vital to public health that we also consider the potential adverse effects of using cannabis daily, especially the varieties that have high levels of THC.
Very important study
Dr. Adrian James, of the Royal College of Psychiatrists, said that this is a good quality study and that its results should be taken seriously. Cannabis carries severe health risks and those who use it are more likely to develop psychosis, he added.
Dr. Michael Bloomfield, a psychiatrist at University College London and head of the Translational Psychiatry Research Group, agrees. He said that the study is important and is a well-conducted piece of research that adds weight to the advice that recreational cannabis users should avoid high-THC weed.