Study: Pot Smoking Increases Risk of Psychosis

(March 1) -- Before Mike Stultz even ate breakfast, the 17-year-old would start his morning by smoking a joint -- only to bump up with a few hits of marijuana every few hours throughout the day. One year later, he was pulled out of college after suffering from a hallucinatory breakdown.

Stultz had become convinced that his life was playing out on a reality television show, complete with hidden cameras and actors playing his family members, friends and doctors. "I would go see the psychiatrist and be thinking the entire time about what I could do to make good TV," he recalls.

Now 24, Stultz remembers a childhood in suburban Toronto that was healthy and stable. But he started smoking pot after breaking up with his first serious girlfriend, and he's convinced it's what triggered his psychological problems.

"There is no question that the weed was involved in my psychosis," Stultz told AOL News. "Mental health problems are not at all common in my family -- no history on either side of my bloodline."

Stultz's story is emblematic of a larger phenomenon that researchers have been trying to pin down for decades: Does frequent marijuana use, especially among teenagers, increase susceptibility to serious mental health problems?

Now a new study, to be published in the March 2 edition of the Archives of General Psychiatry, is addressing the question using sibling-pair analysis. It's a tactic that studies blood-related siblings, to minimize the chance of variables such as social demographics or genetics interfering with results.

Researchers, based at the Queensland Brain Institute, assumed that most sets of siblings experience a similar family dynamic, cultural milieu and exposure to drugs and alcohol. They found that pot smokers in the study group were at increased risk of psychosis.

In 2006, two major medical journals published findings on the possible link. One of the journals, renowned British publication BMJ, even concluded that 10 percent of all psychosis cases were pot-related.

But every study on the issue thus far has been imperfect: Despite controlling for variables like family history or childhood trauma, researchers were hard pressed to conclude that marijuana use caused psychosis, and not the other way around.

Still, the evidence kept piling up.

''No single study is perfect," Wayne Hall, a professor at the University of Queensland, told the Boston Globe after the 2006 reports. ''But the fact that so many individually imperfect studies so consistently find this relationship adds confidence to the conclusion that the relationship is causal."

Of course, the ultimate test of the reefer madness theory would be to assign a group of teens to regularly smoke marijuana. Researchers would likely have an ample supply of volunteers, given that 20 percent of American teens cop to lighting up, but it's not exactly an ethically feasible possibility.

Among the options that do exist, sibling-pair analysis is one of the best bets to minimize variables. In this new study, researchers examined 3,801 Australian teens, of whom 228 were sibling pairs, who had participated in the Mater University Study of Pregnancy in Brisbane and were born between 1981 and 1984.

When researchers contacted the subjects at the age of 21, those who'd been using pot for at least six years were four times more likely to rank in the top quartile of the PDI, a 21-point index that measures symptoms of delusion. They were also twice as likely to exhibit symptoms of psychosis.

Of the 3,801 participants, 65 were diagnosed with psychosis and 223 suffered from some degree of hallucinations. The longer the teens had been smoking pot, the more likely the adverse outcomes.

Of those who smoked pot for more than six years, 3 to 4 percent went on to develop a psychotic disorder before the age of 21. By comparison, lead study author John McGrath estimates that around 1 percent of people worldwide suffer from psychotic ailments.

The connection between siblings reinforced the study's conclusions. Even after controlling for previous symptoms of psychosis and parents with mental illnesses, an individual with more years since first using cannabis than a sibling had a higher PDI score. For every additional year of pot smoking, a sibling's PDI score would increase by one over that of a brother or sister.

The study also reinforces the suspicion that those who are vulnerable to psychosis are inclined to pick up a joint: Individuals who already exhibited "isolated psychotic symptoms" were also more likely to have started using cannabis at some point during the 21-year study period.

It's a seemingly complex relationship, and one that Paul Armentano, a policy analyst with the National Organization for the Reform of Marijuana Laws (NORML), just doesn't buy. While marijuana use has soared in the last few decades, rates of schizophrenia have held steady. "Where's the parallel increase?" he asks.

And people with mental health problems are inclined to ingest "all kinds" of intoxicating substances, of which marijuana is only one, Armentano notes. The legalization advocate admits that marijuana might negatively affect "a very small percentage" of those prone to mental health problems, but he doesn't see reason for outcry.

"We don't outlaw peanuts because a small percentage of people have allergic reactions," he told AOL News. "We educate the community, we regulate where and when peanuts can be exchanged. That seems like it ought to apply to marijuana, too."

Armentano also points to studies that have found no connection between pot and psychosis, like a systematic review out of the United Kingdom just last year. "I don't see any Reuters headlines on those," he said, noting that it's much easier to get research dollars for studies into the adverse effects of marijuana.

For now, the latest research suggests three factors at play: a catalyst for drug use, chronic marijuana smoking and an underlying genetic predisposition to psychotic problems. It's how they intersect that remains a mystery. The triple threat was suggested by a 2005 study out of New Zealand, which tracked 800 people from birth to their mid-20s. Participants with a gene that predisposed them to psychosis, and who smoked pot, were 10 times more likely to suffer a psychotic episode than those with the gene who didn't smoke.

Researchers involved with the latest study also don't know how much marijuana participants were smoking, which McGrath likens to "pack-years in tobacco research" that helped science pin down the health risks of cigarette smoking. "We are still looking at correlation, not causation," he said in an interview with AOL News.

Despite the study's limitations, it offers more heft to a consistent pattern of evidence. And it's a trend that McGrath wants to see reinforced in public health education.

"On the 'balance of probability,' the current data suggests that early cannabis use increases the risk of later psychotic symptoms and psychotic disorders," he said. "It is not as harmless as some people think. We need to educate the community about these risks."

On that, both Armentano and Stultz agree. "Legalization is the best way to harness control over who can use marijuana and teach people about the potential downsides," Armentano said.

Stultz, now a graduate student in international relations, recently suffered a bipolar relapse after cutting back on his medication. He anticipates a lifelong struggle with his mental health, but acknowledges that several of his friends still smoke pot without problems. "Why are my buddies fine and I'm sick?" he asked. "Whether it has to do with weed or not, I'd like to see some research into that."