Recent studies suggest that the key to memory enhancement is the reinforcement of brain synapses - the junctions between nerve cells. The ACh metabolic pathway has become a major biochemical focus in current therapy. Drugs that enhance cognition this way are sometimes referred to as 'smart drugs'. Although AChE inhibitors can improve cognition and daily functioning for patients, not all people improve to the same extent. Some do not change at all, while others continue to deteriorate.
Researchers are still unsure as to why the response is so variable.
Allowing as much as possible of the ACh from functioning neurones to work as normal should delay the disease's progression. The earlier patients are treated, the better. In many cases, the increase in cognitive function would have to be pretty drastic to improve the actual quality of life for patients and their carers. One potential side-effect is raised liver enzyme levels, so patients taking tacrine require regular blood tests to monitor their liver function. Launched in the UK in April 1997, donepezil does not seem to cause liver damage.