MONDAY, Feb. 7 (HealthDay News) -- Smoking marijuana might
trigger an earlier onset of psychosis, a new analysis of previously
published research suggests.
Among people who developed a psychotic illness, those who had
smoked pot developed the illness almost three years earlier than
those who hadn't, the Australian researchers said, and they
speculated that marijuana may actually cause psychosis in some
patients. Their report was published online Feb. 7 and will appear
in the June print issue of the
Archives of General Psychiatry.
But Michael Rice, a psychiatric nurse practitioner at the
University of Nebraska Medical Center in Omaha, isn't convinced
that smoking pot causes psychosis and said there are still several
other theories that could explain the relationship.
One hypothesis is that schizophrenia may be due to an
inflammation in the brain, perhaps due to a virus, and that people
with pre-symptomatic schizophrenia gravitate towards pot because it
has an anti-inflammatory effect, said Rice, who is also associate
director of Nebraska's Behavioral Health Education Center.
"People may be naturally seeking out some substance that tries to reduce the inflammation and the inflammation itself may be related to the psychosis," he explained.
And some neurological and cognitive changes that can predict the
onset of schizophrenia later can be detected as early as 6 or 7
years of age, he added.
Some 16 million people in the United States alone use marijuana
regularly, and most started smoking in their teens. It is the third
most widely used addictive substance after tobacco and alcohol, the
study authors noted.
Earlier studies had found a link between psychosis and marijuana
use, but there's been some controversy over whether the drug
actually causes psychosis. Earlier studies didn't necessarily look
at the timing of onset of psychosis in relation to when people had
started using marijuana.
This meta-analysis (where researchers combine data from numerous
related studies) looked at 83 peer-reviewed articles involving
almost 8,200 individuals who had used marijuana or other drugs and
almost 14,400 individuals who had not.
People who smoked pot developed psychosis 2.7 years earlier than
people with psychosis who did not smoke pot.
Study author Dr. Matthew Large, a senior staff psychiatrist at
Prince of Wales Hospital in Sydney, said, "Heavy cannabis use
starting at a young age carries a very much greater risk than
modest use as an adult."
In general, people who used illicit drugs developed their
psychosis two years earlier than those who didn't. Alcohol use
didn't seem to speed the onset of psychosis.
According to Large, about one in 20 people who start using
marijuana while in junior high school (early teens) will develop
psychosis, while only one in 50 people who use as adults will.
"Given the right genetics, if you smoke pot, it will trigger illness," Rice said. Still, he cautioned that the picture is more complicated than that.
"Schizophrenia is not a single disease. It's 25 to 30 illnesses with similar features, which makes it difficult to come to a single conclusion," he said. "Schizophrenia is the cancer of mental illness."
Another expert agreed.
"Folks in the field appreciate that schizophrenia and other psychotic disorders are really a wide range of various etiologic manifestations," explained Dr. Kathryn Kotrla, associate dean at the Texas A&M Health Science Center College of Medicine in Round Rock. "We don't think that every individual labeled with a psychotic disorder arises from the same cause."
"If there's a plateau and a cliff, when you fall off the cliff, you get labeled as having schizophrenia but there are many steps up to that cliff and each step a risk factor," she said. "We need to think about cannabis as another potential risk factor, another step towards the cliff."
Nevertheless, the study's authors emphasized a need for public
health messages dissuading people -- especially young people --
from using pot.
"The challenge is to get the message to those most at risk, who are in the junior high range," Rice added.
The U.S. National Institute on Drug Abuse has more on
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