Millions of Americans are given antipsychotic medications to treat delirium in the hospital every year - but the drugs don't work, new research reveals.

Delirium is a stater of confusion and mental disturbance that can accompany fever dehydration or any condition or illness that causes brain inflammation.

For 40 years, doctors have been prescribing antipsychotic drugs to patients that become delirious in the hospital, without any clear, proven notion of how, why or even if they worked.

Scientists at Vanderbilt University Medical Center have finally tested the two most commonly-prescribed drugs (haloperidol and ziprasidone) and found that they make no difference in patients' recoveries.

Antipsychotic drugs commonly given to delirious ICU patients are not better for them than placebos, a new Vanderbilt University study reveals

The disorientation, confused speech and even delusions of delirium are scary for patients and doctors alike.

So it's no wonder that doctors might jump to administer a treatment.

But the term and diagnosis 'delirium' has a history of ambiguity dating back to antiquity - and we haven't made all that much progress in narrowing our definition of the state.

Without a clear set of symptoms and causes, a targeted therapy is hard to develop, but that hasn't stopped doctors from treating seven million hospitalized patients for delirium a year.

We do know that delirium can happen to anyone, but is especially common among older patients who are more likely to have long term, chronic or serious ailments.

But haloperidol, for example, can cause side effects like nausea, vomiting and diarrhea, and even raises the risk of death in older patients in particular.

After decades of these drugs being used simply because they had always been used, the Vanderbilt team decided to use a 'gold standard' test to determine whether or not they haloperidol and ziprasidone have any benefits.

They collected data on 21,000 patients at medical centers throughout the US.

Being placed on mechanical ventilation commonly precedes the development of delirium. Of those enrolled, 1,183 had to be moved to intensive care units (ICU) and were either placed on ventilators or went into shock.

A little less than half - 566 - became delirious.

One third of those, randomly selected, were given haloperidol, another third got ziprasidone, and the final third got a placebo in the form of saline solution.

It didn't matter which the patients got, ultimately. By every measure, there were no significant differences in outcomes.

Delirium lasted just as long for patients in each group, they spent about the same average time on ventilations, and had about the same odds of survival, regardless of which drug they received or if they got one at all.

On average, about 73 percent from the entire group survived 30 days from the time they were entered into the city.

That proportion fell to 64 percent after 90 days, which the researchers said reflects how seriously ill patients who develop delirium in intensive care units tend to be.

Antipsychotic drugs didn't seem to make things any worse for the patients that did get them, but that doesn't answer the question of why doctors should bother with another medication at all.

'This research joins other important studies on delirium showing that there clearly is need for improvement in treating and managing this complicated condition,' said Dr Molly Wagster, chief of the Behavioral and Systems Neuroscience Branch in the National Institute of Aging's neuroscience division.

Antipsychotics target dopamine release in the brain, which is thought to be involved in other forms of psychosis, but the study authors suggest their findings my indicate that the same neurotransmitter does not play such a central role in delirium.

Experts increasingly suspect that psychiatric drugs - not just antipsychotics - are over-prescribed based on loose diagnoses, and that the phenomenon may just be fueling mental health disorders.

The Vanderbilt study authors advise greater precision, and suggest that in order to better treat delirium in these very sick patients, we must learn how their states of confusion develop in the brain to begin with.