A British study says it provides new evidence that marijuana use may boost the risk that people who struggle with psychosis will relapse.
But critics said the effect seems to be small, and they questioned the validity of the research.
A study co-author stands by the work, however.
"We
show that pot use causes an increase in the risk of relapse in
psychosis and demonstrate that alternative explanations are unlikely to
be true," said Dr. Sagnik Bhattacharyya, a reader in translational
neuroscience and psychiatry at King's College London.
"It
would be appropriate to at least aim for reduction in pot use in
patients with psychosis if complete abstinence is not realistic,"
Bhattacharyya added.
People
suffering from psychosis lose touch with reality and may hallucinate,
develop delusions and struggle to think and speak normally. Sometimes
psychosis is a symptom of a condition like schizophrenia, bipolar
disorder or depression, according to the National Alliance on Mental
Illness.
Earlier this year, a British study in the journal BMJ Open
linked pot use in psychosis patients to higher levels of
hospitalization and less response to medications. But experts said at
the time that this could be because psychotic patients turn to marijuana
when they're feeling less stable or because genetics make a person
likely to both become psychotic and want to use pot.
In
the new study, researchers looked at 220 patients -- 90 women and 130
men, aged 18 to 65 -- who were diagnosed for the first time with
psychosis. Bhattacharyya said his team tried to expand upon the previous
research by using statistical techniques to look more closely at the
impact of pot.
The researchers
found that the risk that patients would relapse was 13 percent higher
when they used pot than when they didn't. And the odds appeared to go up
when the patients used more pot. This suggests -- but doesn't prove --
that pot use raises the risk of relapse, instead of the other way
around, the researchers said.
They
added that it's not clear how pot use might boost the risk of relapse.
Nor is it clear whether marijuana may have beneficial effects that
aren't being measured, or if the drug may cause more relapses while
making them less severe.
Mitch
Earleywine is a marijuana rights advocate and a professor of psychology
at University at Albany, State University of New York. He said the study
"suffers from most of the problems that plague a lot of the human
research on cannabis and psychosis."
For
one thing, he said, the researchers didn't randomly assign one group of
patients to use marijuana and another to abstain. Then there's the
possibility that a desire for pot is simply a sign that a relapse is
coming, he said.
"In all
likelihood, those who notice a need for cannabis earlier might be the
same ones who are more likely to have another psychotic break whether
they had cannabis or not," he said.
Earleywine also called the increased risk of relapse "ridiculously small."
Study
co-author Bhattacharyya disagreed with this assessment. He said it's
important that the extra risk seen in his study persisted even after the
researchers compensated for factors like higher or lower numbers of
psychotic patients who stopped taking their medications or used other
illegal drugs.
Charles Ksir, a
professor emeritus of psychology and neuroscience at the University of
Wyoming, also criticized the study, saying the increase in risk was
small and unproven. "Perhaps the individual begins to decompensate, and
as part of that process they are a bit more likely to use cannabis," he
said.
What about urging psychotic patients to avoid pot?
"It's
fair to say that anyone who has ever had a psychotic break or has a
schizophrenic relative should stay away from the plant," Earleywine
said.
But Ksir said that
"efforts to influence cannabis use among psychotic patients have not
been successful in getting them to stop or reduce their use."
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