Just 20 years ago levels of tetrahydracannabinol, the compound in cannabis known as THC that makes you high, was between 2% and 4% in most marijuana. By 2013, common strains contained 25% THC, with some testing as high as 37%.
Use of weed of any strength has been linked to mental health disorders, and lab experiments have shown that higher does of THC can cause greater memory impairment and temporary psychotic-like symptoms. But few studies have examined how potency levels may affect behavior in real-world populations.
A new study, published Wednesday in the journal JAMA Psychiatry, surveyed more than 1,000 UK residents who reported marijuana use in the past year. The study found high-potency weed users appear to have a significant increase in the likelihood of developing generalized anxiety disorder than those who smoke less robust strains of marijuana.
In addition, high-potency weed users are more likely to use weed at least once a week, twice as likely to have used illicit drugs within the past 12 months, and more than three times as likely to be tobacco smokers, according to the study which was published Wednesday in the journal JAMA Psychiatry.
"To our knowledge, this study provides the first general population evidence suggesting that the use of high-potency cannabis is associated with mental health[disorders] and addiction," the authors wrote.
"Limiting the availability of high-potency cannabis may be associated with a reduction in the number of individuals who develop cannabis use disorders, the prevention of cannabis use from escalating to a regular behavior, and a reduction in the risk of mental health disorders."
The study used data gathered by the Avon Longitudinal Study of Parents and Children, which asked questions about cannabis use when participants were 24 years of age. Most of the participants said they smoked less potent strains of marijuana (87%), and those who did use more powerful strains were more likely to be male and to have grown up in a lower socioeconomic status. High potency users were also more likely to have used weed an at earlier age, and more likely to have experienced some psychotic events associated with their habit.
Prior studies have also seen associations between high-potency weed and mental health disorders.
A study of first-episode psychosis in more than 400 patients in London found those who said they used higher-potency weed were twice as likely to have a psychotic disorder than those who didn't use marijuana.
A study that looked at more than 900 patients with psychosis in 11 clinics in Brazil and across Europe found daily use of weed to be associated with increased odds of psychotic disorder.
However, there was more than four times the risk of psychotic disorder when high-potency weed was used daily. The study estimated that if high-potency cannabis were no longer available, between 12 and 50 cases of first-episode psychosis could have been prevented among the patients in the study.
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