In a finding that would not please states that have legalized recreational use of marijuana, one study found that about one-third of the psychotic disturbances in London are caused by the use of cannabis.
The study in the Lancet concluded that taking cannabis daily tripled the odds of developing a mental disorder.
"But using forms with high levels of THC active ingredient made users five times more likely to be affected," said the Christian Institute, which released the results.
The study explained: "Between May 1, 2010 and April 1, 2015, we obtained data from 901 patients with first episode of psychosis at 11 sites and 1,237 population controls at these sites. Daily consumption of cannabis was associated with increased chances of psychotic disorder compared to users ever. "
Chances were almost five times higher "for daily use of high-potency cannabis types," according to the study.
Incidence rates for "psychotic disorders were positively correlated with prevalence in controls at 11 sites of high-potency cannabis use … and daily use."
The study said: "The differences in the frequency of daily use of cannabis and in the use of high-potency cannabis contributed to the marked variation in the incidence of psychotic disorders in the 11 sites studied. Given the increasing availability of high-potency cannabis, this has important implications for public health. "
The researchers said that "in the context of well-reviewed epidemiological and biological evidence of a causal link between the heavy use of cannabis and psychotic disorders, our findings have substantial implications for mental health and public health services."
"Education is needed to inform the public about the mental health risks of regular use of high-potency cannabis, which is becoming increasingly available around the world."
The BBC reported that lead researcher Marta Di Fort warned, "If you decide to use high-potency cannabis, keep in mind that there is this potential risk."
"People with psychosis lose touch with reality and can hear voices, see things that are not really there or have confused and delusional thoughts. It's a recognized medical condition and different from getting a drug, "the BBC said.
Researchers at King's College in London found that even removing the more potent forms of drugs would reduce the number of cases of "psychosis."
The Guardian of London reported that powerful cannabis, such as skunk, "has levels of the psychoactive substance tetrahydrocannabinol (THC) above 10%."
A spokesman for the Interior Ministry said: "No illegal drug can be considered safe because there is no safe way to take them. Drugs can devastate lives, ruin families, and harm communities. "
Former Metropolitan Police chief Bernard Hogan-Howe said earlier after the legalization of cannabis in Canada and some states that the UK should reconsider its position on the drug.