Skip to main content


Medically reviewed by Last updated on Mar 20, 2023.

What is Dementia?

Harvard Health Publishing

Dementia is a pattern of mental decline caused by different diseases or conditions. Most commonly, dementia occurs when brain nerve cells (neurons) die, and connections between neurons are interrupted. These disruptions have a variety of causes and usually cannot be reversed.

Alzheimer's disease causes over 60% of all dementias. Vascular disease, such as stroke, is the second most common cause.

Other conditions that can cause dementia include:

In rare cases, dementia is caused by a treatable condition, and it may be partially or entirely reversed if the condition is diagnosed and treated early:

In the developed nations, about 15% of people older than 65 are thought to have dementia.


Symptoms of dementia emerge slowly, get worse over time and limit the person's ability to function.

The first symptom of dementia is memory loss. Everyone has memory lapses from time to time. However, the memory loss of dementia is greater and affects your ability to function. For example, forgetting where you put your car key is normal. Forgetting how to use the key is a possible symptom of dementia.

Often, someone with dementia does not realize that he or she has a problem. Instead, family members recognize that something is wrong.

Along with memory loss, a person with dementia may have trouble with complex mental tasks. They may have difficulty balancing a checkbook, driving, knowing what day it is and learning new things. They may be inattentive, and display poor judgment. Their mood and behavior also may change.

As the disorder progresses, the person may have difficulty speaking in full sentences. They may not recognize their surroundings, or other people. They may have problems with personal care, such as bathing. In some cases, a person with dementia may see or hear things that are not (hallucinations and delusions). They may get very agitated, and may withdraw from other people.


The doctor will ask when memory problems started and how quickly they got worse. This information, together with the person's age, can help suggest a likely diagnosis. For example:

However, the exact cause of dementia in any individual can often be difficult to determine.

To diagnose dementia, a doctor looks to see if a person's memory gets progressively worse, along with at least one of the following:

Doctors test people by testing memory and attention. A commonly used tool to screen for dementia is the Mini Mental State Exam. It consists of 11 short assessments, such as asking the person what day and year it is or have the person count backward from 100 by sevens (100, 93, 86, etc.). If the person answers correctly, dementia is less likely.

Laboratory tests can narrow down the possible causes. Some tests include:

Expected duration

In most cases, dementia gets worse and cannot be cured. A person with dementia may live for months, years or decades, depending on the cause of the dementia and whether the person has other medical conditions.

In the rare cases in which dementia is caused by a treatable condition, such as infection, metabolic disorder or depression, the dementia usually is reversed after treatment.


Most of the causes of dementia cannot be prevented. Good personal health habits and medical care, however, can prevent some types of dementia. Here are some things you can do:

Keeping your mind active and your body fit may help to prevent mental decline and reduce or postpone memory loss. If you get daily physical exercise and continue to challenge your brain throughout life, you can help to protect your brain against mental decline.


Sometimes the cause of dementia can be reversed, such as vitamin B12 deficiency or an underactive thyroid. Treating these conditions may improve the dementia. Other reversible factors that can contribute to symptoms include overuse of alcohol and depression.

People with vascular dementia may show less mental decline if their blood pressure is controlled, they stop smoking, lower LDL (andquot;bad" cholesterol), exercise regularly and maintain a healthy weight.

In some people, medications for Alzheimer's may help with behavioral symptoms and perhaps slow down the mental decline. They may delay the need for placement into a nursing home. Acetylcholinesterase inhibitors, such as donepezil (Aricept), galantamine (Razadyne) and rivastigmine (Exelon), can be prescribed for mild to moderate Alzheimer's dementia. Memantine (Namenda) is approved for moderately severe Alzheimer's dementia.

These same medications are sometimes used to treat the dementia associated with Lewy body disease.

Two new treatments for Alzheimer's disease using monoclonal antibodies directed against brain amyloid beta have been granted accelerated approval by the U.S. Food and Drug Administration (FDA). They are aducanumab (Aduhelm) and lecanemab-irmb (Leqembi), which may slow and even potentially halt progression of the disease.

Depending on the cause of the dementia, several specialists may be involved in care, including neurologists, psychologists, psychiatrists or geriatric doctors. Nurses and social workers play a very important role in care.

Here are some easy to implement aspects of care that help ease symptoms:

Treatment options

The following list of medications are in some way related to or used in the treatment of this condition.


The outlook for dementia depends on the cause and can vary by individual. For example, early treatment of dementia caused by a vitamin deficiency can lead to full recovery of memory. If stroke is the cause, the person's memory loss can remain stable for years.

Drugs may slow the rate of decline for some people with Alzheimer's disease.

In most cases, however, the disorder gradually gets worse. Depending on the cause, the person's age, general health and the availability of treatments, life expectancy can be as short as a few months or as long as 15 to 20 years.

When to call a professional

Call your doctor if you or a loved one is having difficulty with any of the following:

A person with dementia may also exhibit the following types of behaviors:

Additional info

National Institute of Neurological Disorders and Stroke

American Geriatrics Society

Alzheimer's Association

Alzheimer's Disease & Related Dementias

Learn more about Dementia

Treatment options

Care guides

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.