Pot-induced psychosis may signal schizophrenia

By Anne Harding Anne Harding
– Mon Nov 3, 4:59 pm ET


NEW YORK (Reuters Health) – People who have long-lasting psychotic episodes after smoking marijuana may be exhibiting early signs of schizophrenia, researchers reported Monday in the Archives of General Psychiatry.

"Cannabis-induced psychosis," in which a person loses touch with reality and the symptoms persist for at least 48 hours, is an established psychiatric diagnosis, but it is controversial, Dr. Mikkel Arendt of Aarhus University in Risskov, Denmark, and colleagues note in their report. There has been little research on the condition, and doctors have a hard time distinguishing it from other psychiatric disorders or developing a specific list of symptoms by which to characterize it.

In a previous study, Arendt and colleagues found that nearly half of people who had an episode of cannabis-induced psychosis went on to develop schizophrenia within the next six years. In the current study, the researchers looked at the genetic roots of both conditions by comparing the family histories of 609 people treated for cannabis-induced psychosis and 6,476 who had been treated for schizophrenia or a related psychiatric condition.

They found that individuals treated for post-pot smoking psychotic episodes had the same likelihood of having a mother, sister or other "first-degree" relative with schizophrenia as did the individuals who had actually been treated for schizophrenia themselves. This suggests that cannabis-induced psychosis and schizophrenia are one and the same, the researchers note. "These people would have developed schizophrenia whether or not they used cannabis," Arendt explained in comments to Reuters Health.

Based on the findings, the researcher says, "cannabis-induced psychosis is probably not a valid diagnosis. It should be considered schizophrenia."

It's "very common" for people to have psychotic symptoms after using marijuana, such as hearing voices, feeling paranoid, or believing one has some type of special ability, Arendt said. But these symptoms typically last only an hour or two. "It's a very important distinction, this 48 hours criterion," he said.

Other researchers have shown that pot smoking roughly doubles the risk of being diagnosed with schizophrenia, and that people who use marijuana and go on to develop schizophrenia become psychotic earlier than people with the illness who don't use cannabis, Arendt added.

It's unclear whether smoking marijuana causes schizophrenia or not, but if it does, according to the researcher, it's likely a gradual process. Nevertheless, he said, "the consensus is pretty much you should not use cannabis if you want to avoid an increased risk of schizophrenia."

Anyone who experiences an extended psychotic episode after using marijuana should get help, Arendt advised. These symptoms could represent an opportunity for early diagnosis and treatment of schizophrenia, he added, and the earlier people with this illness begin treatment, the better their prognosis.

SOURCE: Archives of General Psychiatry, November 2008.