March 20 (UPI) -- Smoking high-potency cannabis, used daily, has been linked to diagnosis of conditions like schizophrenia, paranoia and other psychosis disorders, new findings say.
About 50 percent of new cases of psychosis disorders diagnosed in Amsterdam were linked to use of high-potency cannabis, according to a study published Tuesday in The Lancet. Additionally, 30 percent of new psychosis cases diagnosed in London were also associated with high strains of the drug.
"The use of cannabis with a high concentration of THC has more harmful effects on mental health than the use of weaker forms," Marta Di Forti, a researcher at King's College London and study lead author, said in a news release. "Our findings also indicate for the first time how cannabis use affects the incidence of psychotic disorder at a population level."
Of more than 1,200 adults who participated in the study, 30 percent of the people who experienced a first psychosis event used cannabis every day. And 37 percent of people with first psychosis events used high-potency cannabis every day.
High-potency cannabis was classified as having THC content over 10 percent.
Overall, daily cannabis users were three times more likely to suffer a psychotic episode than those who never used the drug. That risk increased to five times for high-potency users.
The researchers found that throughout 11 cities in Europe and one in Brazil, one in five new cases of psychosis was linked to daily marijuana use and one in 10 with high-potency cannabis.
The researchers say the study does not prove a cause-and-effect relationship, but the association between mental health events and heavy marijuana use has been shown in previous studies.
Researchers in the new study estimate that banning high-potency strains of marijuana like "trainwreck," "gorilla glue" and "hindu kush" would cut psychosis cases across Europe by 12 percent. They they also predict that first-time psychosis cases in Amsterdam would fall from 38 to 19 per 100,000 annually, and in London from 46 to 32 per 100,000.
"As the legal status of cannabis changes in many countries and states, and as we consider the medicinal properties of some types of cannabis, it is of vital public health importance to consider the potential adverse effects that are associated with daily cannabis use, especially high potency varieties," Di Forti said.