It found painkillers significantly cut agitation in dementia patients.
On the other hand, antipsychotics have a powerful sedative effect, can worsen dementia symptoms, and increase the risk of stroke or even death.
They are often given to patients whose dementia makes them aggressive or agitated.
However, researchers from Kings College, London and Norway speculated that the behaviour might sometimes be caused by pain, which patients were unable to express in other ways.
They studied 352 patients with moderate or severe dementia in nursing homes in Norway.
Half were given painkillers with every meal, the rest continued with their usual treatments.
After eight weeks, there was a 17 per cent reduction in agitation symptoms in the group being given painkillers – a greater improvement than would have been expected from treatment with antipsychotics.
The researchers concluded that if patient’s pain was properly managed, doctors could reduce the number of prescriptions for antipsychotic drugs.
Professor Clive Ballard, one of the report authors and director of research at the Alzheimer’s Society, said the finding was significant.
“At the moment, pain is very under-treated in people with dementia, because it’s very hard to recognise. I think this could make a substantial difference to people”s lives – it could help them live much better with dementia,” he said.