A compound found in marijuana can treat schizophrenia as effectively as antipsychotic medications, with far fewer side effects, according to a preliminary clinical trial.

Researchers led by Markus Leweke of the University of Cologne in Germany studied 39 people with schizophrenia who were hospitalized for a psychotic episode. Nineteen patients were treated with amisulpride, an antipsychotic medication that is not approved in the U.S., but is comparable to other medications that are.

The rest of the patients were given cannabidiol (CBD), a substance found in marijuana that is thought to be responsible for some of its mellowing or anxiety-reducing effects. Unlike the main ingredient in marijuana, THC, which can produce psychotic reactions and may worsen schizophrenia, CBD has antipsychotic effects, according to previous research in both animals and humans.

Neither the patients nor the scientists knew who was getting which drug. At the end of the four-week trial, both groups showed significant clinical improvement in their schizophrenic symptoms, and there was no difference between those getting CBD or amisulpride.

"The results were amazing," says Daniel Piomelli, professor of pharmacology at the University of California-Irvine and a co-author of the study. "Not only was [CBD] as effective as standard antipsychotics, but it was also essentially free of the typical side effects seen with antipsychotic drugs."

Antipsychotic medications can potentially cause devastating and sometimes permanent movement disorders; they can also reduce users' motivation and pleasure. The new generation of antipsychotic drugs also often leads to weight gain and can increase diabetes risk. These side effects have long been known to be a major obstacle to treatment.

In the German study, published online in March by the journal Translational Psychiatry, weight gain and movement problems were seen in patients taking amisulpride, but not CBD.

"These exciting findings should stimulate a great deal of research," says Dr. John Krystal, chair of psychiatry at Yale University School of Medicine, who was not associated with the research. He notes that CBD not only had fewer side effects, but also seemed to work better on schizophrenia's so-called "negative symptoms," which are notoriously hard to treat.

Negative symptoms include social withdrawal, blunting of pleasure and lack of motivation, which commonly occur in schizophrenia. Since current antipsychotic medications can themselves cause the same problems, however, it wasn't clear whether CBD was better than amisulpride at treating these symptoms, or whether CBD simply caused fewer side effects to begin with.

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