Disorders

What is Alzheimer's disease?

Reviewed April 2026 by Joel Salinas, MD, MBA, MSc, FAAN

Definition: Alzheimer’s disease is an irreversible, progressive brain disease that slowly destroys memory, thinking skills, and eventually the ability to carry out daily tasks. While there is no cure, several medications could slow the disease or help with symptoms.

Alzheimer’s disease is the most common cause of dementia among older adults. It’s a group of symptoms that can affect memory, speech, language, judgment, personality, behavior, mood, and much more—especially daily function. It gets worse over time and can cause a variety of symptoms from memory loss and difficulty finding the right word to irritability, anxiety, and visual hallucinations.

Brain changes can begin decades before symptoms appear. Amyloid plaques—clumps of misfolded proteins—build up outside brain cells. Tau tangles, another type of misfolded proteins, form inside the cells. Over time, brain cells stop working and die, causing the brain to shrink.

More than 7.4 million Americans age 65 and older are living with Alzheimer’s disease. Without a cure, that number could rise to 13 million by 2050. About one in three older adults dies with Alzheimer’s disease or other causes of dementia, and nearly two-thirds are women.

Alzheimer’s disease is fatal. After diagnosis, many people age 65 and older may live four to eight years, though some live much longer. How fast the disease gets worse is different for each person.

What are the symptoms of Alzheimer’s disease?

Symptoms go beyond occasional forgetfulness and begin to interfere with daily life. Common signs include:

  • Memory loss that disrupts daily life. This includes forgetting things you just learned or asking the same questions over and over.
  • Trouble planning or solving problems. For example, difficulty following a recipe or keeping up with bills.
  • Difficulty with tasks you do all the time, like driving to a place you know or making a grocery list.
  • Confusion about time or place. Losing track of dates, seasons, or how you got somewhere.
  • Trouble seeing or judging distances. This can make driving harder.
  • New problems finding the right word. You may stop mid-sentence or forget a simple word.
  • Misplacing things and not being able to find them again.
  • Poor judgment, such as ignoring grooming or making bad money choices.
  • Pulling away from work, social activities, or favorite hobbies. Joining conversations and taking part in the things you enjoy can become harder.
  • Changes in mood or personality. You may become confused, fearful, or anxious.

Alzheimer’s disease progresses over time. In later stages, people need more help with daily tasks and eventually become fully dependent on others for care.

What are the causes and risk factors of Alzheimer's disease?

Although there are many risk factors for Alzheimer’s disease, the biggest risk factor is age. Risk rises sharply with age, especially after 65, but age alone does not cause Alzheimer’s disease.

Genes also play a role. The APOE-e4 variant is strongly linked to higher risk, but having it does not mean a person will develop Alzheimer’s disease. In fewer than 1% of cases, rare gene changes directly cause the disease, often before age 65. Risk is also higher if a parent or sibling has had Alzheimer’s disease.

Some risk factors can be changed. The 2024 Lancet Commission identified 14 factors linked to dementia risk, including hearing loss, high blood pressure, high cholesterol, diabetes, obesity, smoking, heavy alcohol use, depression, low physical activity, social isolation, head injury, vision loss, low education, and air pollution. Addressing these factors may lower risk.

Some risk factors can’t be changed. Black older adults are twice as likely to develop dementia due to Alzheimer’s disease compared to White older adults; Hispanic older adults are one and a half times more likely. Research suggests this gap is caused mainly by differences in what’s called structural and social determinants of health, not genetics alone. These determinants are the conditions in which we’re born, grow, live, and work. They include our life experiences, access to timely care, and greater risk for other health conditions.

How is Alzheimer's disease diagnosed?

There is no single test for Alzheimer’s disease. Diagnosis usually includes a neurologist reviewing medical history, performing a neurologic exam, and testing memory, language, attention, and other thinking skills. A family member or close friend is often asked to describe any changes they’ve noticed.

Neurologists may also use biomarkers linked to Alzheimer’s disease. These include spinal fluid tests, PET scans that look for amyloid and tau, and, in some settings, blood tests. Biomarkers can support diagnosis, but they do not replace a full evaluation.

Memory and thinking problems can also be caused by treatable conditions such as depression, sleep apnea, thyroid problems, vitamin deficiencies, or head injury. A neurologist can help sort out whether symptoms are due to Alzheimer’s disease, another condition, or typical aging.

What treatments are available for Alzheimer's disease?

There is no cure for Alzheimer’s disease, and there are no treatments to reverse the disease and its symptoms. However, Alzheimer’s disease treatments may help manage symptoms and, for some people with early disease, slow decline.

Medications to slow Alzheimer's disease
Lecanemab (Leqembi) and donanemab (Kisunla) target amyloid in the brain and may slow decline in some people with early Alzheimer’s disease. These IV treatments are not cures and are only appropriate for certain patients.

These medicines can cause rare but serious side effects, so treatment requires careful screening. More common side effects include small areas of brain swelling or small areas of bleeding called ARIA (amyloid-related imaging abnormalities). These require close monitoring with brain scans to help understand when to pause or stop treatment.

Medications for thinking and behavior symptoms
Several FDA-approved medicines can ease thinking symptoms for a time, but they do not stop the disease. Donepezil, rivastigmine, and galantamine may help with memory, thinking, and behavior symptoms at milder stages of the disease, while memantine may help with these symptoms beginning at the moderate stage. Other medicines may be used for specific symptoms, such as agitation or sleep problems, when appropriate.

Non-drug treatments
Non-drug approaches can improve quality of life and are often the first step for behavior or mood changes. Options may include exercise, music, art, structured routines, and mentally engaging activities.

Lifestyle factors
Healthy habits support brain health. Stay active, eat a heart-healthy diet, get enough sleep, stay socially engaged, manage blood pressure and blood sugar, protect hearing, avoid smoking, and prevent head injury.

Caring for and navigating Alzheimer’s disease

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Frequently asked questions

What is the difference between Alzheimer’s disease and dementia?

Dementia is an umbrella term—it doesn’t name just one disease. It describes a group of symptoms (like memory loss, confusion, trouble thinking, planning, or finding words) that are serious enough to make daily life harder. Alzheimer's disease is a common cause of dementia, but not the only one. Identifying the type of dementia someone has helps guide treatment, planning, and expectations. Brain changes can also show up in stages, and not every stage is dementia.

Sometimes a person feels that their memory or thinking has changed, but tests still come back normal. Neurological care providers call this subjective cognitive decline. Normal tests are reassuring, but they do not rule everything out. Early changes in the brain can begin before any test can catch them.

Other times, memory or thinking problems are large enough to show up on tests, but the person can still manage most daily tasks completely on their own. Neurological care providers call this mild cognitive impairment, or MCI. It sits between typical aging and dementia.

Dementia is the stage where symptoms clearly affect daily life. Things like handling money, taking medicine, or staying safe at home become hard to do alone.

What are the early warning signs of Alzheimer’s disease?

Early warning signs often go beyond typical aging and start to affect daily life. These may include forgetting recently learned information, repeating questions, trouble with familiar tasks, confusion about time or place, problems finding the right word when speaking, and changes in judgment, mood, or personality.

Can Alzheimer’s disease be prevented or delayed?

There is no proven way to prevent Alzheimer’s disease or stop it from progressing, but healthy habits may help lower risk or delay symptoms. These include staying physically active, managing blood pressure, cholesterol, and diabetes, eating a healthy diet, avoiding smoking, staying socially connected, and keeping the brain engaged.

What should I do if I think I or a loved one has Alzheimer’s disease?

If memory, thinking, or behavior changes are interfering with daily life, talk to a health care professional as soon as possible. Early evaluation can rule out other treatable causes, give you answers, and help you plan for care and support.