"The risk of developing pneumonia is not associated with long-term use, but is the highest shortly after starting the drug," study authors Dr. Rob van Marum of the University Medical Center Utrecht and Dr. Wilma Knol of the hospital Tergooiziekenhuizen in Hilversum, the Netherlands, say in a statement. However, they caution "all anti-psychotic drugs may be associated with pneumonia in elderly patients."

Anti-psychotic drugs are used frequently in elderly patients to treat psychosis and behavioral problems associated with dementia and delirium. The study authors say they found up to 40 percent of nursing home residents may be prescribed anti-psychotics. They point out other studies have not only suggested more than half of the anti-psychotics may be prescribed for inappropriate reasons but have associated the drugs with an increased risk of death and illness.

The underlying mechanism for this association remains unclear, the authors say, but they stress that clinicians may need to monitor patients for sedation after initiation of anti-psychotic medication and that a careful weighing of the possible risks is recommended before starting anti-psychotic treatment in elderly people.