Alzheimer's disease is characterised by memory loss and difficulties with thinking. These problems may be due to a deficiency in a brain chemical called acetylcholine. Acetylcholine helps transmit messages between nerve cells. Acetylcholine is degraded by an enzyme called "acetylcholinesterase". ZT-1 is a new drug derived from a plant extract already used in China for memory disorders, which blocks the action of the enzyme and restores adequate levels of acetylcholine.