People showing the first signs of schizophrenia could be prevented from developing full-blown psychosis by early treatment with antipsychotics such as Eli Lilly’s Zyprexa, according to the results of a clinical trial.

But the level of side effects with treatment was an issue for patients – particularly weight gain – and make it hard to gauge whether the approach should be offered in clinical practice, according to the researchers behind the work, published in the May 1 issue of the American Journal of Psychiatry.

The side effects and stigma associated with treatment for mental illness have to be weighed up against a modest effect in delaying psychosis with Zyprexa, and this is a close judgment call, according to the study authors.

After one year’s treatment, 16% of the people given Zyprexa went on to develop psychosis, compared to 38% of those on placebo, a result which neared but did not reach statistical significance. Moreover, in the year after treatment stopped, the patients who had taken olanzapine experienced increasing symptoms and a third went on to become psychotic, further suggesting that olanzapine may have delayed psychosis in this high-risk group.

At the same time, more than two thirds of patients in both arms of the study had dropped out, for a variety of reasons including side effects, and this made the results hard to interpret. Patients taking Zyprexa gained an average of 20 pounds during therapy.

This exacerbated patient recruitment problems in the trial, mainly because the target population – adolescents with mild, psychosis-like symptoms – are hard to identify.

The authors of the study, called PRIME (Prevention Through Risk Identification, Management, and Education), said the number of patients in the study made it hard to draw conclusions, but “nearly significant differences suggest that olanzapine might reduce the conversion rate and delay onset of psychosis.”

Thomas McGlashan of Yale University, the study’s lead author, said that while the drop-out rates were disappointing, the results indicated a possible role for medications in preventing schizophrenia and further studies are warranted.