Scientists say they have found a drug which could treat some of the most distressing symptoms of dementia.
Carers may be screamed at, or even hit
As many as half of patients can become agitated, and may scream at their carers - or even hit them.
University of Rochester researchers treated patients with quetiapine, usually used to treat schizophrenia.
But UK experts said the small study, presented to an international dementia conference in Philadelphia, America should be treated with caution.
Quetiapine (Seroquel) belongs to a class of drugs called atypical anti-psychotics.
Professor Pierre Tariot, who led the research at the University of Rochester, is also a paid consultant to AstraZeneca, which makes Seroquel.
The team studied 333 people in nursing homes for 10 weeks.
They were given either quetiapine or a dummy pill.
It was found the active medication reduced agitated behaviour in patients around 20% more often than the dummy pill.
In addition, the behaviour of patients on the medication was more likely to be rated as "improved" or "very much improved," compared to other patients not on the medicine, by doctors and nurses who did not know who was taking what.
The team said there were other anti-psychotic medications currently used to treat agitation, which are effective in just 15 to 20% of patients.
Such medications can cause side effects of weight gain, high cholesterol, sleepiness and Parkinson's-like movement difficulties. Some have also been linked to higher incidences of stroke.
The research so far has found no severe side effects linked to quetiapine, although some patients did experience sleepiness.
Pierre Tariot, professor of psychiatry, medicine, and neurology, who led the study, said: "One of the most stressing and vexing changes in behaviour in patients with dementia is agitation, which occurs in about half of patients at some point in their illness .
"This behaviour can be terrifying to the family and is one of the major reasons many families end up placing their loved ones in nursing homes."
He added: "If quetiapine remains free of the most worrisome side effects through further studies, that would represent an advantage and would offer a new therapeutic option for patients and their families."
The findings of a larger scale study funded by the US National Institutes of Health, expected next year, will compare several atypical anti-psychotics for treating Alzheimer's and schizophrenia.
Professor John Mayer, of the UK's Alzheimer's Research Trust, said: "Experienced clinicians often turn to atypical anti-psychotics to treat agitation in dementia patients."
He added: "We need to know whether this drug works as well in patients with Alzheimer's disease as patients with related disorders such as Dementia with Lewy bodies in which patients hallucinate and can show very disturbed behaviours."
But Professor Clive Ballard, director of research for the UK's Alzheimer's Society, told BBC News Online: "This study has shown some modest benefit, but I would need to see further data before we could say if it was meaningful."
He said the UK's Committee on the Safety of Medicine had recommended that two other drugs in the same class, risperidone and olanzapine, should not be used to treat agitation in dementia patients because they had been linked with an increased risk of stroke.
Professor Ballard added: "The CSM issued a caution on quetiapine because there was some evidence of a risk of stroke, but it did not make a definitive statement because there wasn't definitive information."