LONDON, July 27 (Xinhua) -- A British study showed Friday that using cannabis may increase the risk of developing psychotic illnesses such as schizophrenia later in life.

    Researchers from the University of Bristol, Imperial College and Cambridge University reviewed 35 studies that tracked tens of thousands of people for periods ranging from one year to 27 years to examine the effects of marijuana on mental health.

    They found that people who used marijuana had roughly a 41 percent higher chance of developing a psychotic disorder later in life, and the likelihood increases with increasing marijuana use, with heavy users three times as likely as non-users to develop mental illnesses.

    They reported the findings in the latest issue of British medical journal The Lancet which is published Friday.

    Marijuana is the most frequently used illegal substance in many countries. About 20 percent of young adults report taking pot at least once a week, according to government statistics in Britain.

    According to the researchers, if marijuana does cause psychosis, it could account for at least one in every 10 cases of diagnosed psychotic illness.

    Previous research has suggested a link between cannabis and schizophrenia-like symptoms such as paranoia and hallucinations.