Using marijuana increases the
risk of one day developing a psychotic illness such as schizophrenia, according
to a study that provides some of the strongest evidence yet linking the drug to
a mental disorder.
Marijuana is one the most
commonly used illegal substances in many countries with up to 20 percent of
young people in places like Britain reporting either some use or heavy use,
British researchers said, citing government statistics.
Many consider it on par with
alcohol or tobacco but the results shows marijuana poses a danger many smokers
underestimate, said Stanley Zammit, a psychiatrist at
Cardiff University and the University of Bristol, who worked on the study.
The researchers found that
marijuana users had a 41 percent increased chance of developing psychosis
marked by symptoms of hallucinations or delusions later in life than those who
never used the drug. The risk rose with heavier consumption.
"If you compare other
substances like alcohol or tobacco it may not be as harmful, but what we are
saying is neither is it completely safe," Zammit
said in a telephone interview.
Other findings have
highlighted the link between marijuana use and the risk of schizophrenia-like
symptoms such as paranoia, hearing voices and seeing things that are not there.
But this study marks one of
the most comprehensive, thorough and reliable reviews of its kind and should
serve as a warning, two Danish researchers wrote in an accompanying comment in
the Lancet medical journal, which published the study on Friday.
