The loss of a neurotransmitter called acetylcholine is quite significant in the brains of people with Alzheimer’s disease, three of the four drugs available are cholinesterase inhibitors which stop an enzyme called acetylcholinesterase from breaking down acetylcholine. This group of drugs include Donepezil (Aricept), Rivastigmine (Exelon) and Galantamine (Reminyl). Side effects can include nausea, diarrhoea and vivid dreams.
The fourth drug is called memantine an NMDA receptor antagonists, it is neuroprotective in that it protects brain cells by blocking the effects of surplus glutamate. It can be much better tolerated than cholinesterase inhibitors and it’s usually added as the disease progresses. It was originally patented as Ebixa but is now also available as generic memantine.