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Cannabis boosts risk of psychosis

Michael Hopkin

Nature

Wednesday 01 Dec 2004

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Using cannabis during adolescence or early adulthood increases the risk of
developing psychotic symptoms, according to a study that tracked almost
2,500 young people. Crucially, those who are already predisposed to such
problems are at a disproportionately greater risk when using the drug.

Psychiatrists found that those using cannabis have, on average, a 6%
greater chance of suffering psychotic symptoms such as schizophrenia,
delusions and paranoia, compared with those who don't take the drug. But
for the 10% of people who are already vulnerable to such problems, such as
those with a family history of schizophrenia, this figure leaps to 25%.

What's more, these figures depend on the level of drug intake, particularly
for those already in danger, says Jim van Os of Maastricht University in
the Netherlands, who led the study. "If you are vulnerable, then the more
cannabis you use, the greater your risk of psychosis," he told a press
conference in London on 1 December.

Overall, his team found that volunteers who were predisposed to mental
problems and frequently smoked cannabis had roughly a 50% chance of
suffering psychotic symptoms within the four years of the study, which took
place in Germany.

Drugs bust

Cannabis has already been linked to psychosis, but experts were unsure
whether the drug itself causes problems, or whether psychotics are simply
more likely to use it. The latest study, published in an online version of
the British Medical Journal1, is the first to track the subsequent effects
of cannabis use, rather than examining the past behaviour of psychiatric
patients.

Neuroscientists suspect that the effects are down to cannabis's main
psychoactive ingredient, delta-9-tetrahydrocannabinol (THC). This compound
stimulates brain cells to release more of the neurotransmitter dopamine, a
process that initially stimulates pleasure but can later also lead to
paranoia or hallucinations.

"We're not saying that cannabis is the major cause of psychosis," says
Robin Murray of the Institute of Psychiatry in London, who also studies the
link between cannabis and mental health. Other factors that cause mental
stress, such as emigrating, may have a greater effect, he suggests.

In fact, members of the study group, which consisted of 14-24-year-olds,
had a 15% chance of showing symptoms at some point during the four years
even if they did not smoke cannabis and had no predisposition to psychosis.

Nonetheless, psychiatric carers need to be more aware of the link between
cannabis and psychosis, argues Zerrin Atakan, also of the Institute of
Psychiatry. "There's a shortage of knowledge and training," she says. "What
I see as a clinician is that patients see the connection [at first], but
when they start to get better they remember the pleasurable aspects of
cannabis."

Cannabis advocates point to the drug's pain-relieving qualities as evidence
that it is beneficial and should be prescribed for use in treating
conditions such as multiple sclerosis. And those who argue that it should
be legalized for recreational use claim that the drug's feel-good benefits
outweigh any potential problems.

On the level

The problem is that black-market cannabis can contain wildly differing
levels of THC, says van Os. "In the Netherlands concentrations are getting
very high, up to 20% in some places. Youngsters think this is normal, but
many of the old hippies in Amsterdam refuse to take it; they are used to 2
or 3%," he says.

"I personally believe it should be legalized so it can be regulated," says
Atakan. "Then when you buy joints they will be labelled with how much THC
they contain."

Encouraging openness and awareness is the key, agrees van Os: "Youngsters
are very aware of their acute reactions to cannabis. For example, one in
seven get paranoid ideas that they find distressing." Encouraging cannabis
users to discuss such problems could have the knock-on effect of reducing
the drug's public-health impact, he suggests.

 

 

 

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