The four drugs are an anti-amyloid (Alzhemed), an inhibitor of brain cell death (Dimebon), an "Alzheimer's vaccine" (Immunotherapy Treatment AN1792), and a drug normally used to treat diabetes (Avandia).
Alzheimer's disease is thought to be caused by build up of a protein called amyloid beta which forms plaques and tangles in the brain, kills off brain cells and interferes with neuron to neuron signalling.
Approved treatments for Alzheimer's currently only relieve symptoms for a couple of years and make little impact on the amyloid beta build up and the progress of the disease. Vice president for Medical and Scientific Relations at the Alzheimer's Association, Dr William Thies said that:
"Amyloid as a cause for Alzheimer's and a primary target for therapies and preventions must be thoroughly tested."