Chemo Brain


For years cancer survivors have worried about, joked about, and been frustrated by the mental cloudiness they sometimes notice before, during, and after cancer treatment. Even though its exact cause isn’t always known, this mental fog is commonly called chemo brain. Patients have been aware of chemo brain for some time, but only recently have studies been done that could help to explain it.

Doctors have known for years that radiation treatment to the brain can cause thinking and memory problems. Recently, they have found that chemo is linked to some of the same kinds of problems. (To read more about radiation and its effects, see Understanding Radiation Therapy: A Guide for Patients and Families.) Research shows that some cancer drugs can cause certain kinds of changes in the brain. But it also shows that chemo and radiation aren’t the only things that can cause thinking and memory problems in people with cancer.

Though the brain usually recovers over time, the sometimes vague yet distressing mental changes cancer patients notice are real, not imagined. They might last a short time, or they might go on for years. These changes can make people unable to go back to their school, work, or social activities, or make it so that it takes a lot of mental effort to do so. Chemo brain changes affect everyday life for many people, and more research is needed to help prevent and cope with them.

What is chemo brain?

Here are just a few examples of what patients call chemo brain:

  • Forgetting things that they usually have no trouble recalling (memory lapses)
  • Trouble concentrating (they can’t focus on what they’re doing, have a short attention span, may “space out”)
  • Trouble remembering details like names, dates, and sometimes larger events
  • Trouble multi-tasking, like answering the phone while cooking, without losing track of one task (they are less able to do more than one thing at a time)
  • Taking longer to finish things (disorganized, slower thinking and processing)
  • Trouble remembering common words (unable to find the right words to finish a sentence)

Doctors and researchers call chemo brain “mild cognitive impairment.” Most define it as being unable to remember certain things and having trouble finishing tasks or learning new skills. But some doctors call it chemo brain only if it doesn’t go away or get better over time. How long it lasts is a major factor in how much it affects a person’s life.

For most people, brain effects happen quickly and only last a short time. Others have long-term mental changes. Usually the changes that patients notice are very subtle, and others around them may not even notice any changes at all. Still, the people who are having problems are well aware of the differences in their thinking. Many people don’t tell their cancer care team about this problem until it affects their everyday life.

For someone who has lost some brain function, even short-term problems with thinking and memory can be scary. Some people may have trouble remembering simple things, like closing doors or turning off lights. Others may notice that their brain doesn’t work as quickly as it used to. These kinds of brain problems can cause trouble at work and at home. People who notice problems with their thinking may feel even more upset if their doctors blame it on aging or act like it’s nothing to worry about. It’s distressing to wonder if you’ll ever be able to do your job again, or if you’ll get lost on the way to a place you’ve been to dozens of times.

Brain problems are hard to study.

Clearly, we need to know more about chemo brain. But there are certain issues that make brain problems hard to study. For instance, researchers sometimes use different tests to measure the problems with thinking and memory, so the results may not compare well with each other. Some people report changes that are so mild that their brain tests look normal and doctors don’t have a good way to measure the changes. One study even noted that changes like this are reported by people with cancer who didn’t get chemo. This may mean the tests used in the study weren’t sensitive enough to pick up smaller changes. It also suggests that something other than chemo might have caused the problems. Still, chemo is one of the causes of brain problems in some people with cancer. Many of these people have brain function problems that are directly related to cancer or its treatment, and most of these problems do show up on testing.

There are also differences in when certain kinds of brain problems happen. Some researchers have tested brain function a few weeks after treatment, others months or even years later. If the problem only lasts a few weeks with no long-term changes, late testing can miss it. If the changes last more than a year but the testing stops after 6 months, no one knows how long they last. Beyond the chemo brain symptoms that start during and just after treatment, it is clear that there are some cases where brain symptoms start and even get worse after treatment is over. Many cancer treatments, including certain kinds of chemo and radiation, can cause short-term, long-term, and delayed problems.

Another timing problem in studying chemo brain is that most studies didn’t test the patients before treatment to compare to results after treatment. In studies that did tests before treatment, some people were seen to have brain function problems before treatment was even started. So it’s possible that the cancer itself causes some of the problems, or that some other related problem caused brain function to decline. Studies are needed that test people before the treatment and then follow up to look for changes over time.

Differences in how chemo brain is defined can also make it hard to get a handle on how often it happens. There is a wide range of estimates of how many people get chemo brain. One expert noted that, among people who get chemo, between 15% and 70% have brain problems. Another expert put the upper limit of the range at 50%. So based on these numbers, the risk of chemo brain (for people who get chemo) can be higher than 1 out of 2 or as low as 1 in 6. This may not take into account people with brain or thinking problems that may be caused by their cancer, radiation, or other causes.

When it starts, how long it lasts, and how much trouble it causes can vary a lot. So the term “chemo brain” is not completely accurate. Still, it’s what most people call it right now.

What causes brain problems during cancer treatment?

Studies suggest that there may be more than one cause of chemo brain, especially for the short-term symptoms. Some people with cancer have very real brain problems even though they have not had chemo. Still others notice problems when getting hormone treatments, such as estrogen blockers or androgen deprivation therapy (treatments to lower testosterone levels). For some, problems start after surgery. Along with chemo, many different problems can worsen brain function.

For instance, brain problems could be caused or worsened by any one or any combination of these factors:

  • The cancer itself
  • Other drugs used as part of treatment (such as steroids, anti-nausea, drugs used for surgery, or pain medicines)
  • Low blood counts
  • Sleep problems
  • Infection
  • Tiredness (fatigue)
  • Hormone changes or hormone treatments
  • Other illnesses, such as diabetes or high blood pressure
  • Nutritional deficiencies
  • Patient age
  • Depression
  • Stress, anxiety, or other emotional pressure

Most of these cause short-term problems, and get better as the underlying problem is treated or goes away. A few, such as depression, can cause long-lasting brain problems unless the cause is treated.

So far, there is no known way to prevent chemo brain. For some people, treating their cancer will mean trouble with thinking, memory, planning, and word finding.

Studies of brain problems related to cancer and its treatment

Imaging tests have shown that in some patients, the parts of the brain that deal with memory, planning, putting thoughts into action, monitoring thought processes and behavior, and inhibition are smaller after chemotherapy. In some studies, these problems were more common in those who got high-dose chemo (such as chemo used for stem cell or bone marrow transplant). But a 2009 study of people who were tested before stem cell transplant noted that some problems had started before the transplant was done, and that memory greatly improved over the next 18 months. At that time some still had trouble with slower reaction times and fine muscle coordination, but other functions were better. In another series of studies, brain problems that were present 2 years after treatment were much better 4 years after treatment.

A 2011 study looked at patients who had a stem cell transplant from another person, which involves both high-dose chemo and immune-suppressing drugs. The researchers tested these patients early then observed them for 5 years after the transplant. Although their thinking problems had improved after a year, more than 40% still had mild brain problems after 5 years. The patients had improved in all other areas tested, but they were still somewhat low on hand speed and dexterity as well as word recall.

Pictures of the brain have shown lower resting brain activity in breast cancer survivors treated with chemo when compared with those who were not treated with chemo. These changes were still seen on scans of some women 5 to 10 years after treatment stopped. And during memory testing, these women had to call on and use larger areas of their brains than women who had not gotten chemo.

It’s not all related to chemo and radiation, though. A small 2012 study looked at women after breast cancer surgery, before any other treatment was given. When tested, about 1 in 4 showed problems with word skills and about 1 in 7 had memory issues. Although surgery, surgical drugs, or other factors may have had some effect, the women who reported worse brain problems also reported higher stress levels.

In people with brain problems, tests of memory usually show the person is slow to learn new things, and they take longer to recall what they know. Response or reaction times slow down; attention and concentration often suffer. Most often, tests find that the person with chemo brain has more trouble in using recalled information (executive function), and in using language.

More studies are being done to try to better understand chemo brain. What is known for sure is that brain slowdown is a real problem that affects both men and women. Most of these people will notice that the problems get better over time. But others will have to learn ways to deal with brain problems that don’t go away.

What can I do to manage brain problems?

Day-to-day coping

Experts have been studying memory for a long time. There are many resources that might help you sharpen your mental abilities and manage the problems that might come with chemo brain. Some things that you can do are:

  • Use a detailed daily planner. Keeping everything in one place makes it easier to find the reminders you may need. Serious planner users keep track of their appointments and schedules, “to do” lists, important dates, websites, phone numbers and addresses, meeting notes, and even movies they’d like to see or books they’d like to read.
  • Exercise your brain. Take a class, do word puzzles, or learn a new language.
  • Get enough rest and sleep.
  • Exercise your body. Regular physical activity is not only good for your body, but also improves your mood, makes you feel more alert, and decreases tiredness (fatigue).
  • Eat your veggies. Studies have shown that eating more vegetables is linked to keeping brain power as people age.
  • Set up and follow routines. Pick a certain place for commonly lost objects and put them there each time. Try to keep the same daily schedule.
  • Don’t try to multi-task. Focus on one thing at a time.
  • Ask for help when you need it. Friends and loved ones can help with daily tasks to cut down on distractions and help you save mental energy.
  • Track your memory problems. Keep a diary of when you notice problems and the events that are going on at the time. Medicines taken, time of day, and the situation you are in might help you figure out what affects your memory. Keeping track of when the problems are most noticeable can also help you prepare. You’ll know to avoid planning important conversations or appointments during those times. This will also be useful when you talk with your doctor about these problems.
  • Try not to focus on how much these symptoms bother you. Accepting the problem will help you deal with it. As many patients have noted, being able to laugh about things you can’t control can help you cope. And remember, you probably notice your problems much more than others do. Sometimes we all have to laugh about forgetting to take the grocery list with us to the store.

Telling others

Another thing you can do to better manage chemo brain is tell family, friends, and your health care team about it. Let them know what you are going through. You may feel relieved once you tell people about the problems you sometimes have with your memory or thinking.

You are not stupid or crazy—you just have a side effect that you have to learn to manage. Even though this is not a change that is easy to see, like hair loss or skin changes, your family and friends may have noticed some things and may even have some helpful suggestions. For instance, your partner may notice that when you are rushed, you have more trouble finding things.

Tell your loved ones what they can do to help. Their support and understanding can help you relax and make it easier for you to focus and process information.

Talk with your doctor or cancer care team

If brain problems cause you trouble at work, you may need to talk with your doctor to try and pinpoint what is causing your brain fog and what can be done about it. This is especially important for people whose problem lasts for more than a year and keeps causing trouble in their daily lives.

It helps a lot if you have a diary or log of the situations you have trouble with. It also helps to know some of the things that make the problem worse or better. For instance, are they worse in the morning or evening? Do you have more trouble when you are hungry or tired? Does it help to nap, walk, or have a snack? Your doctor will want to know when the problems started and how they affect your daily life.

  • Write down questions about the problems you have to talk over with your doctor. Take them to your appointment along with your memory tracking log. Ask what may be causing the problems, and find out if there’s anything the doctor can offer to help you.
  • Bring a list of all the medicines you take, including herbs, vitamins, supplements, and those you take on an “as needed” basis.
  • Take a friend or family member with you to help you keep track of what was said during the visit. They can also describe the changes they see if the doctor wants a different viewpoint of how your brain problems are affecting you.
  • If your memory and thinking problems keep causing trouble in your daily life, ask your doctor if you might be helped by a specialist such as a neuropsychologist. These professionals can test you and may recommend ways to help you better handle the problems.

You may need to visit a larger hospital or cancer care center to find neurologists, psychologists, or neuropsychologists who are experts on testing brain function, including chemo brain. Ask if you can get a referral to one of these specialists who can help you learn the scope of your problem and work with you on ways to manage it. You’ll want to find out what your insurance will cover before you start.

Can brain problems be prevented?

The causes of brain problems related to cancer and its treatment are still being studied, and at this time there is no known way to prevent them. Chemo brain seems to happen more often with high doses of chemo, and is more likely if the brain is also treated with radiation. But because chemo brain is usually mild and most often goes away in time, chemo that is proven to work against the cancer should not be changed to try to prevent this side effect.

What’s being done about chemo brain?

Now that chemo brain has clearly been linked to cancer and its treatment, studies are being done to learn more about it. Some studies are looking to find out which chemo drugs and other treatments are more closely linked to chemo brain. Researchers are also looking at possible ways to prevent brain problems. For instance, certain drugs are being looked at to protect the brain, but these have yet to be tested in humans.

Researchers are studying other aspects of cancer treatment that may lead to long-term mental changes, too. For example, they are looking at the types and doses of chemo the patients had, anemia, other cancer-related symptoms (like tiredness), and genetic differences among people to see if these factors are linked to a higher risk of brain problems.

Doctors are also studying ways to help survivors who are still having trouble thinking.

Future directions

Looking at how brain problems happen

Studies have shown clear evidence of nerve damage from at least some forms of chemotherapy. But studies of the effects of chemo drugs on brain cells are rare. Special imaging tests must be used to help pinpoint areas of increased and decreased activity in the brain. This is a focus of ongoing research. Scientists must find out which nerve cells or brain cells are at risk during cancer treatment to develop ways to reduce damage, save brain function, and maintain the quality of life in long-term survivors.

So far, early studies in the lab and in animals suggest that certain chemo drugs may harm some nerve cells even after the drug is stopped. Again, more research is needed to see if this happens in humans, too.

There is more concern about chemo brain today because cancer treatment studies have shown better outcomes using more aggressive, high-dose drug schedules. Newer targeted drugs affect certain pathways that are part of nerve cell formation and stem cell function, which also is a cause for concern. Learning which nerve cells are affected may help scientists test new drugs for this side effect.

Protecting the brain

Cancer experts are looking into treatment options that may protect the brain from chemo side effects. Targeted drugs that focus on the cancer cells and spare normal cells, such as brain and nerve cells are being studied.

Treating brain problems

Researchers are looking at medicines that are now used for problems like depression, attention-deficit hyperactivity disorder (ADHD), Alzheimer disease, and dementia. These might serve as possible treatments for chemo brain that doesn’t get better, but more testing is needed.

Looking for other links to brain problems

Genetic differences that may make some people more likely to have symptoms of brain problems are being explored. One particular gene, called APOE, is being looked at closely. Research has shown that a version of this gene, called E4, is linked to Alzheimer disease. When E4 is present, there is an increased chance of thinking problems after traumatic brain injury, too. Studies are being done to find out if people who have the E4 gene and get chemotherapy have a higher risk of developing long-term chemo brain.

Recognizing that chemo brain can be a treatment side effect was the first step. Doctors and researchers are now trying to measure how exactly it affects patients’ brains and cause changes. This important information can help them find ways to not only treat brain problems, but in the future, help to prevent them. Clinical trials are going on, and many more are needed.

To learn more

More information from your American Cancer Society

We have selected some related information that may also be helpful to you. These materials may be ordered by calling us at 1-800-227-2345 or read on our Web site,

Understanding Chemotherapy: A Guide for Patients and Families (also in Spanish)

Understanding Radiation Therapy: A Guide for Patients and Families (also in Spanish)

Talking With Your Doctor (also in Spanish)

Talking With Friends and Relatives About Your Cancer (also in Spanish)

Anxiety, Fear, and Depression (also in Spanish)

Caring for The Patient With Cancer at Home: A Guide for Patients and Families (also in Spanish)

Chemotherapy Principles: An In-Depth Discussion of the Techniques and Its Role in Cancer Treatment

Nutrition for the Person With Cancer During Treatment: A Guide For Patients and Families (also in Spanish)

Childhood Cancer: Late Effects of Cancer Treatment

National organizations and Web sites*

Along with the American Cancer Society, other sources of information and support include:

American Psychosocial Oncology Society (APOS)
Toll-free number: 1-866-276-7443
Web site:

  • Provides referrals for local counseling, therapists, and social support services to help connect patients and/or caregivers to psychiatrists, psychologists, nurses, and social workers skilled in the management of cancer-related distress.

Toll-free number: 1-800-813-4673
Web site:

  • Web site offers fact sheets on chemo brain in the “Side Effects” section. Also provides free professional support services to anyone affected by cancer: people with cancer, their loved ones, and caregivers, including telephone counseling, online support groups, free educational materials, and telephone workshops.

American Psychological Association (APA)
Toll-free number: 1-800-374-2721
TTY: 202-336-6123
Web site:

  • Provides a hotline to get information and discuss psychological concerns. Also makes referrals to state psychological associations to find a psychologist (sometimes called a counselor or therapist) in your area.

*Inclusion on this list does not imply endorsement by the American Cancer Society.

No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-227-2345 or visit


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Last Medical Review: 05/17/2012

Last Revised: 05/30/2012

Source: American Cancer Society