MARIJUANA INCREASES PSYCHOSIS RISK: REPORT

LONDON - Using marijuana seems to increase the chance of becoming psychotic,
researchers reported in an analysis of past research that re-ignites
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, was published
yesterday in the medical journal the Lancet.

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

The researchers said they could not 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 UK and the US. 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 a list of 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.

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 Deepak Cyril D'Souza, an
associate professor of psychiatry at Yale University, who was not
involved in the study.

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, Compton said.

Scientists cannot rule out that pre-existing conditions could have led
to both marijuana use and later psychoses, he said.

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 now 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
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."

In the UK, the government will soon reconsider how marijuana should be
classified in its hierarchy of drugs. In 2004, it was downgraded and
penalties for possession were reduced. Many expect marijuana will be
bumped up to a class "B" category, with offenses likely to lead to
arrests or longer jail sentences.

Two of the authors of the study were invited experts on the Advisory
Council on the Misuse of Drugs Cannabis Review in 2005. Several
authors reported being paid to attend drug company-sponsored meetings
related to marijuana, and one received consulting fees from companies
that make anti-psychotic medications.