There appears to be only a low chance of developing psychosis as a result of using cannabis, a review of existing research has suggested.
After a review of existing research, Ian Hamilton, a lecturer in mental health at York University, concluded that stopping people using the drug would have a relatively low impact on the public's mental health.
"The link between cannabis and psychosis has been investigated by researchers since the drug became popular in the 1960s," Mr Hamilton told The Independent.
"A new review of research carried out since then has concluded that ‘at a population level the increased risk is weak and the vulnerabilities relatively rare'.
"To put this in perspective we would need to prevent 23,000 people using cannabis to prevent one case of psychosis."
However, Mr Hamilton stressed there were “caveats” to this overall picture.
“Most of the seminal studies on this link were carried out when people were using lower potency cannabis,” he said.
“Few studies have been conducted since the emergence of higher potency cannabis sometimes referred to as 'skunk’.
“Higher potency cannabis contains less cannabidiol (CBD), which is believed to offer some protection from developing problems such as psychosis, but higher levels of tetrahydrocannabinol (THC) which can trigger psychosis.”
He also warned heavy users of the drug were more likely to experience mental health problems.
“What was clear from all the research is the more cannabis you use the greater your risk of developing psychosis,” Mr Hamilton said.
“We know that only nine per cent of users consume 73 per cent of the cannabis consumed. And for those with schizophrenia cannabis exacerbated their symptoms.”
Cannabis could be regulated to introduce a degree of “quality control”, he suggested.
“This would provide users with information about the strength of cannabis on offer, something they usually only discover after exposure in the current unregulated market,” Mr Hamilton said.
The “greatest risk” from using cannabis was from the tobacco normally taken with it in the UK. IN the US, people tend to use cannabis on its own, he said.
“For many young people, their introduction to tobacco is via a cannabis joint increasing the chance of developing tobacco dependence,” Mr Hamilton wrote.
Cannabis around the world
Cannabis around the world
Farmers destroy cannabis plantations under Moroccan police supervision in the northern Moroccan Larache region, pictured here in 2006
Growing business: Cannabis on sale at River Rock Wellness
Oaksterdam in Oakland, California, is the world's only university dedicated to the study and cultivation of cannabis
Alain Jocard/AFP/Getty Images
A cannabis smoker marks the start of the new law by the Space Needle in Seattle
Cannabis growing wild in China, where it has been used to treat conditions such as gout and malaria
Uruguay has voted to make the country the first to legalize marijuana
A groundswell of support from the public led to full legalisation in Colorado
A man smokes licenced medicinal marijuana prior to participating in the annual Hemp Parade, or 'Hanfparade', in support of the legalization of marijuana in Germany on August 7, 2010 in Berlin, Germany. The consumption of cannabis in Germany is legal, though all other aspects, including growing, importing or selling it, are not. However, since the introduction of a new law in 2009, the sale and possession of marijuana for licenced medicinal use is legal.
Sean Gallup/Getty Images
The UK latest figures show 2.3 million people used cannabis in the last year
Tourists visiting Amsterdam will not be banned from using the city’s famous cannabis cafes
These 25 cannabis plants, seized in Merseyside police, could have generated a turnover of £40,000 a year
12/13 San Francisco
April 20, 2012: People smoke marijuana joints at 4:20 p.m. as thousands of marijuana advocates gathered at Golden Gate Park in San Francisco, California. The event was held on April 20, a date corresponding with a numerical 4/20 code widely known within the cannabis subculture as a symbol for all things marijuana.
A cannabis users' association will pay the town of Rasquera more than €600,000 a year for the lease of the land
“Perhaps regulation could help to break this habit as information about such risks would be less hampered by the constraints of a substance that falls under the Misuse of Drugs Act.
“So although the public health message about the link between cannabis and psychosis has been a difficult one to communicate the clearest advice we can offer with the greatest potential health benefit health is leave out the tobacco from your joint.”Reuse content