Research into the benefits of drugs used to treat sufferers of Alzheimer's disease has indicated that all three of them can help patients.
Intensive studies using Aricept, Razadyne and Exelon found that they were effective in easing some of the symptoms of the disease, despite working in different ways.
Small improvements were seen in general mental functioning, enabling sufferers with mild and moderate symptoms to carry on with everyday tasks.
Jacqueline Birks, the author of the review, studied the effects of the drugs on 7,298 patients from Europe, North America and Australia and the results are published in the latest issue of The Cochrane Library.
Those taking Aricept experienced fewer side effects, although this could be attributed to the fact that the other drugs are prescribed in increasingly higher doses, while the study suggested that the earlier a patient starts taking the drugs, the better.
George Grossberg, a specialist in Alzheimer's treatment, agreed with this approach and said: "Patients who come to drugs later, even as little as six months later, never catch up with those who were on drug from the outset."
Ms Birks concluded that longer trials were necessary and that the issue of cost effectiveness needed to be addressed.