February 8, 2011
Study Links Psychiatric Diseases To Marijuana
Researchers said that when people who smoke marijuana become mentally ill, psychiatric diseases start earlier than it would if they did not smoke pot.
This means that serious psychiatric diseases that might not have shown up until kids were in their teens or twenties if they had not started smoking as young as 12.
Dr. Matthew Large said in an interview with Reuters Health that the link between using pot and developing serious mental illness is strongest in the youngest smokers.
"We have to (tell) people who have marijuana in their pockets not to give it to younger people," said Large, who headed up the research at the University of New South Wales in Sydney, Australia.
The researchers looked at thousands of patients with psychotic disorders like schizophrenia. People with psychotic disorders lose touch with reality, which usually starts in adolescence or young adulthood.
The authors of the new study found that the psychotic symptoms began about 3 years earlier than in those who had not been marijuana users.
People with schizophrenia often have hallucinations and delusions and they also tend to have unusual or bizarre behavior, social problems, and general difficulty in coping with life. The National Institute of Mental Health said that about 2.4 million American adults, or about one in every 100 people over age 18, have schizophrenia.
Dr. Michael T. Compton at George Washington University Medical Center in Washington D.C. told Reuters reporter Nancy Lapid that no one has been able to prove that smoking marijuana actually causes psychotic disorders like schizophrenia, but the new research adds to "growing evidence" that it does, at least in some people.
The researchers also all agreed that a number of studies had already suggested that people develop schizophrenia at a younger age if they have been using pot.
Large and Compton and their colleagues systematically combined and analyzed data from 83 studies involving over 22,000 people with psychotic disorders like schizophrenia to get a better sense of the evidence.
"Those who used marijuana had an earlier age at onset of the disorder, by (about 32 months) on average, than those who had not used marijuana," Compton said in e-mail to Reuters Health.
The researchers wrote in their article published in the Archives of General Psychiatry that the reasons lie in the way the individual studies might have been done.
The team made sure during their analysis to account for several factors that authors of the individual studies might not have considered. For example, psychosis develops earlier in boys than in girls, but Large and Compton found that even when they adjusted for that difference, the pot smokers still developed psychotic symptoms earlier.
Also, older people are less likely to be smoking pot than younger patients. The researchers found that when taking that factor into account that marijuana users developed mental illness at a younger age.
They also tried to see whether their findings could be explained by the year the research was done, whether the research had been done according to good scientific principles, and whether the investigators had defined the start of mental illness according to the date it was diagnosed instead of the date the symptoms started. However, they kept coming back to the same result, which was people with psychotic disorders who smoked marijuana had symptoms of mental illness at a younger age than those who did not use pot.
The team did not look at whether family history of psychosis played a role in determining who was most vulnerable to marijuana's apparent early-triggering effect.
One study found that compared to people who did not use marijuana, people over 18 who did use it had twice the risk of mental illness, but kids under 15 had five times the risk.
Large said that there are two main messages to take away from this study. One is that there is probably something in marijuana that triggers schizophrenia. "Schizophrenia is still a mystery," he said. "Psychotic illnesses are horrible for the people who have them, and terrible for their families too."
He said the second is that public health campaigns on the dangers of marijuana are focusing on older users and overlooking the pre-teens and young adolescents who get their pot from older peers and even older siblings.
"Even if the onset of psychosis were inevitable (for a particular individual)," Large's team writes, "an extra 2 or 3 years of psychosis-free functioning could allow many patients to achieve the important developmental milestones" of adolescence.
That extra time could allow a young person to finish school and gain other skills that might reduce the lifelong disability that so often accompanies mental illnesses.
Large said he is not going to bother traveling around to announce his results to other doctors where as most studies like his are presented at medical conferences. He said that he wants to talk about his results in public forums.
"I'm not a marketing expert," he said, "but we have to find a way to tell young kids to hold off."
We might not be able to convince them to never use pot, he added, but they need to wait until they're older.
On the Net:
- University of New South Wales
- George Washington University Medical Center
- Archives of General Psychiatry