STUDY: POT MAY INCREASE PSYCHOSIS RISK, STOKING TALK OF DRUG'S DANGERS

LONDON -- Using marijuana seems to increase the chance of becoming
psychotic, researchers report in an analysis of past research that
reignites the issue of whether pot is dangerous.

The new review suggests that even infrequent use could raise the small
but real risk of this serious mental illness by 40 percent.

Doctors have long suspected a connection and say the latest findings
underline the need to highlight marijuana's long-term risks. The
research, paid for by the British Health Department, is being
published today in The Lancet medical journal.

"The available evidence now suggests that cannabis is not as harmless
as many people think," said Dr. Stanley Zammit, one of the study's
authors and a lecturer in the department of psychological medicine at
Cardiff University.

The researchers said they couldn't prove that marijuana use itself
increases the risk of psychosis, a category of several disorders of
which schizophrenia is the most commonly known.

Marijuana is the most frequently used illegal substance in many
countries, including the United Kingdom and the United States. About
20 percent of young adults report using it at least once a week,
government statistics show.

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

They looked for psychotic illnesses as well as cognitive disorders,
including delusions and hallucinations, bipolar disorder, depression,
anxiety, neuroses and suicidal tendencies.

They found that people who used marijuana had roughly a 40 percent
higher chance of developing a psychotic disorder later in life. The
overall risk remains very low.

For example, Zammit said the risk of developing schizophrenia for most
people is less than 1 percent. The prevalence of schizophrenia is
believed to be about five in 1,000 people. But because of the drug's
wide popularity, the researchers estimate that about 800 new cases of
psychosis could be prevented by reducing marijuana use.

For "heavy users" of pot, those who used it daily or weekly, the risk
for psychosis jumped to a range of 50 percent to 200 percent.

Dr. Wilson Compton, a senior scientist at the National Institute on
Drug Abuse in Washington, called the study persuasive.

"The strongest case is that there are consistencies across all of the
studies," and that the link was seen only with psychoses -- not
anxiety, depression or other mental health problems, he said.

Scientists think it is biologically possible that marijuana could
cause psychoses because it interrupts important neurotransmitters such
as dopamine, which can interfere with the brain's communication systems.