More than half of U.S. Parkinson’s disease patients are taking antipsychotic medications, despite U.S. Food and Drug Administration warnings that the practice could pose a risk of harm, a new study finds.

In 2005, the FDA started requiring that antipsychotic medications carry black box warnings saying that the drugs could pose risks to people with Parkinson’s disease. Antipsychotics have been shown to worsen symptoms of dementia and psychosis in Parkinson’s patients.

In analyzing Veterans Affairs data collected between 2002 and 2008, University of Pennsylvania researchers studied Parkinson’s patients with dementia, Parkinson’s and patients without dementia, and patients with dementia and psychosis but no Parkinson’s disease.

They found that roughly half of the patients with Parkinson’s disease and psychosis received an antipsychotic drug prescription, and that use of the drugs was higher in patients with both Parkinson’s disease and dementia than among those without dementia.

The study was published in the July issue of the Archives of Neurology.