Alzheimer's disease (AD), also called Alzheimer disease or simply Alzheimer's, is the most common cause of dementia, afflicting 24 million people worldwide. Alzheimer's is a degenerative and terminal disease for which there is currently no known cure. In its most common form, it occurs in people over 65 years old although a less-prevalent early-onset form also exists. The disease can begin many years before it is eventually diagnosed. In its early stages, short-term memory loss is the most common symptom, often initially thought to be caused by aging or stress by the sufferer. Later symptoms include confusion, anger, mood swings, language breakdown, long-term memory loss, and the general withdrawal of the sufferer as his or her senses decline. Gradually the sufferer loses minor, and then major bodily functions, until death occurs. Although the symptoms are common, each individual experiences the symptoms in unique ways. The duration of the disease is estimated as being between 5 and 20 years.

The symptoms of Alzheimer's disease are generally reported to a physician when memory-loss causes concern, and on suspecting Alzheimer’s disease, the physician or healthcare specialists will confirm the diagnosis with a behavioral assessment and cognitive tests, often followed by a brain scan.