STUDY LINKS MARIJUANA USE WITH PSYCHOSIS RISK

LONDON (AP)-- 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 medical journal The Lancet.

"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 with
schizophrenia being the most commonly known.

There could be something else about marijuana users, "like their
tendency to use other drugs or certain personality traits, that could
be causing the psychoses," Zammit said.

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,
according to government statistics.

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 thought to be about five in 1,000 people. But because of the
drug's popularity, the researchers estimate about 800 new cases of
psychosis could be prevented by reducing marijuana use.

The scientists found a more disturbing outlook for "heavy users" of
pot, those who used it daily or weekly: Their risk for psychosis
jumped to a range of 50 percent to 200 percent.

One doctor noted that people with a history of mental illness in
their families could be at higher risk. For them, marijuana use
"could unmask the underlying schizophrenia," said Dr. Deepak Cyril
D'Souza, an associate professor of psychiatry at Yale University, who
was not involved in the study.

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 cannot rule out that existing conditions could have led to
both marijuana use and later psychoses, he added.

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

Some experts say governments should work to dispel the misconception
that marijuana is a benign drug.

"We've reached the end of the road with these kinds of studies," said
Dr. Robin Murray of King's College, who had no role in the Lancet
study. "Experts are now agreed on the connection between cannabis and
psychoses. What we need now is for 14-year-olds to know it."