A controversial drug used to treat mild to moderate Alzheimer's disease has been proved to be useful also in the later stages, improving the memory and understanding in patients with a severe form of dementia.

A study conducted at the Karolinska Institute that looked at 194 patients showed that Donepezil, which is not licensed in the UK to treat severe Alzheimer's, could improve mental function in severe cases.

Scientists compared the effect of the drug with that of a placebo in the elder patients who took part in the study and found that those who took the medicine were able to do daily tasks and were less reliant on nursing care, their speech, memory and communication skills also improving.

Professor Bengt Winblad, who led the 6-month study, stated: "We got impressive results. Donepezil slows and can reverse some aspects of deterioration of cognition and function in individuals with severe Alzheimer's who live in nursing homes. We now have a drug that will improve the intellectual capacity of the elderly with severe Alzheimer's disease."

Still, another study conducted last week reported the death of 11 people with a different form of dementia after they were given Donepezil, commercially known as Aricept, during a clinical trial. Nearly 650 patients in the trial received the drug, while there were no deaths among the 326 people who received a placebo. Side-effects of Donepezil included diarrhea and hallucinations.

Around 2 million people worldwide suffer from Alzheimer's disease. By 2040, the number of people with dementia is expected to rise to 81 million.