The Difference Between Delirium and Dementia

Dementia and delirium are both health conditions that change a person’s ability to think clearly and care for themselves. They do share some similar signs and symptoms. But they have different causes, treatment, and outcomes.

Delirium is seen as a medical emergency that needs to be treated right away. But it can often be mistaken for dementia. In some cases, these conditions can occur at the same time. Learn how the two are different, and what you can do to help a person who has signs of either or both.

What is delirium?

  • Delirium is a sudden change in a person’s mental state that fluctuates over short periods of time. A person will have trouble paying attention or following a conversation. Thinking and speech may be confused, illogical, unclear, and unpredictable.

  • A person’s mental state may vary from agitated and watchful to sluggish and sleepy.

  • Delirium is a medical emergency. Usually, there is some underlying cause.

  • Delirium is treated by finding the cause. Once the cause is treated, the delirium can go away.

What is dementia?

Dementia is a range of signs that a person’s brain is losing function. With dementia, a person’s ability to think, remember, and communicate with others gets weaker over time. This process occurs over years and usually progresses slowly. At first, a person may sometimes be forgetful or confused. Questions will be asked over and over. Basic information may be forgotten. Over time, he or she will have trouble following directions and doing daily tasks. The person will have trouble talking with and understanding others. Eventually, a person with dementia may forget who people are and not know where he or she is. The person may also be moody or restless.

Knowing the difference




Common signs

Signs include forgetfulness and confusion. The person will have trouble speaking with and understanding others. This occurs over long periods of time.

Signs include sudden changes in mental state. Changes may range from agitation to tiredness.

When signs appear

There is a slow change in mental state and behavior over months or years.

There is a sudden change in mental state and behavior over hours or days.

Thinking and attention

The person may often seem confused. Over time, the person’s thinking will not be sensible or logical. As the disease worsens, the person will not be able to focus well. He or she will often not be able to talk with or understand others clearly. In some cases, the person may see or hear things that others can’t (hallucinations). The person will not be able to remember events that just happened, and lose memory of events in the past. The person may not remember who people are, or where they are. The person may not recognize common objects.

The person may be confused and disoriented. The person may have trouble focusing and talking with others. It is likely that the person will not be able to tell a healthcare provider about his or her symptoms. The person may see or hear things that others can’t (hallucinations). The person may not be able to remember something that just happened.

Getting a diagnosis

A person with signs of dementia or delirium will need to be diagnosed correctly. In some cases, you can help. You can tell the healthcare provider how the person's mental state is different from their normal state. This can help the provider diagnose the problem.

Healthcare providers will look at different parts of a person's health. They will look at what medicine a person is taking. They will find out if the person has an infection, or if he or she has an illness that has gotten worse. They may talk with the person to learn more about his or her mental state. And they may do tests to see if there may be a cause for delirium.

When to get medical help

Someone with dementia may also have signs of delirium. This can show that there is another problem.

If someone-–with or without dementia-–has sudden changes in mental state, call his or her healthcare provider right away. Or call 911 or your local emergency number. Tell the healthcare provider about the signs of delirium you have seen.