Yes, forgetfulness, poor concentration and slower thinking during and after chemotherapy are real and common; up to about 3 in 4 patients notice some degree of it during treatment [4]. It is usually mild and eases over the months that follow; in a large study of women with breast cancer, the extra effect of chemotherapy on memory and concentration had gone by one year [6]. But in some patients (up to about 1 in 3), a problem, even if small, lasts for years [4]; regular exercise, memory training, notes and reminders, and enough sleep all help [1, 9, 10].
Key points
- Chemo brain is real: many patients have forgetfulness, poor concentration and slower thinking during and after chemotherapy; up to about 3 in 4 people during treatment [4].
- Chemotherapy is not the only cause: the cancer itself, tiredness, poor sleep, pain, anxiety and depression, menopause and other treatments such as hormone therapy, immunotherapy and radiotherapy to the brain also play a part [1, 3].
- It usually gets better with time: in a large study, the extra effect of chemotherapy had gone by one year [6]; in some patients, a mild problem lasts for years [4, 7].
- What helps: regular exercise, memory training and coaching, notes and phone reminders, enough sleep, and treating tiredness, anxiety and depression [1, 2, 9, 10].
- It is different from Alzheimer's disease: chemo brain is usually mild and eases with time [6]; in two large studies of older women with breast cancer, chemotherapy did not raise the risk of dementia [11, 12].
- Tell your doctor: if forgetfulness is making work, study or driving difficult, talk to your doctor so that treatable causes can be checked [2, 3].
What is chemo brain, or forgetfulness after chemotherapy?
Many patients say their mind feels "foggy" during or after cancer treatment. This is called "chemo brain" or "brain fog", and in medical language "cancer-related cognitive impairment" [2]. Common signs [2, 3]:
- difficulty learning new things or remembering them
- not being able to recall familiar names and words in the middle of a conversation
- difficulty concentrating on what you are doing and finishing tasks
- difficulty following what other people are saying
- slower thinking and disorganised tasks
How severe it is varies from person to person: some people notice only a very small change and others have more difficulty [1]. In studies, memory, concentration, speed of thinking and the ability to plan are affected most [2]. Sometimes memory test results are normal while the person clearly feels the change [2]; take this experience seriously and tell your doctor.
Why does chemotherapy cause forgetfulness?
The exact cause is not yet fully understood, and usually several factors play a part together [2, 4]:
- chemotherapy; and also radiotherapy to the brain and immunotherapy [1]
- hormone therapy: in some studies, tamoxifen tablets were linked with slightly weaker memory [2, 3]
- the cancer itself: up to about 3 in 10 patients have problems with memory and concentration even before chemotherapy starts [4]
- tiredness, poor sleep and pain [2, 3]
- anxiety, depression and the emotional strain of the illness [2, 3]
- menopause [3]; read about menopause after cancer treatment: Early menopause and hot flushes after cancer treatment
- older age, physical frailty, other illnesses and drinking alcohol [3]
Most studies have been in women with breast cancer [4], but chemo brain is seen in other cancers too; for example, in one study patients with lymphoma had more decline in memory than healthy people for up to a year after chemotherapy [8].
How long does chemo brain last? Does it get better?
Chemo brain may start during treatment or after it [1]. For most people it eases with time, but getting better can take months [4, 6]:
- In a large study of women with breast cancer, those who had chemotherapy plus hormone tablets complained of forgetfulness more in the first months than those who had hormone tablets alone; but by one year this difference had gone [6].
- In another large study, a decline in memory and concentration was seen for at least 6 months after the end of chemotherapy [5]. In patients with lymphoma and breast cancer, it continued for up to a year, and women with breast cancer still reported it more than healthy people at 2 years [8].
- In some patients (up to about 1 in 3), a problem, even if mild, lasts for years [4]. In a study of women treated about 20 years earlier with one of the older chemotherapy regimens, memory test results were on average lower than in women of the same age who had not had cancer [7].
So in most cases chemo brain is not permanent. In the meantime, use the strategies below and tell your doctor about any changes.
What can I do about chemo brain? Ways to help memory and concentration
- 1
Notes and reminders
Write down your tasks and important information and keep the list with you. Use a daily planner, a calendar and phone reminders for appointments and medicines [1].
- 2
Do difficult tasks at your best time of day
Do the tasks that need the most concentration at the time of day when you feel best [1].
- 3
- 4
Regular exercise
Exercise lowers stress and helps you feel more alert [1]. In a study of women who had memory problems after chemotherapy for breast cancer, 6 months of regular exercise (about 4 hours a week, including brisk walking and strength training) reduced complaints of forgetfulness, tiredness and depression and improved quality of life, although memory test results did not change [10]. Read: Can I exercise during cancer treatment?
- 5
Memory training and learning ways to work around problems
"Cognitive rehabilitation" means learning new ways to remember things and organise tasks, together with mental exercises [3]. In one study, a 15-week online brain-training programme done at home reduced complaints of forgetfulness, and the effect was still there 6 months later; tiredness and anxiety were lower too [9]. Puzzles, brain games and meditation also help some people [1, 3].
- 6
Get treatment for anxiety, depression and tiredness
These make memory and concentration worse, and they can be treated [2]. Read: Anxiety, depression and fear of cancer coming back and Fatigue from cancer and its treatment.
What should I do at work, school or university?
If forgetfulness is making work or study difficult, you do not have to cope with it alone. Put the harder tasks at the times when you feel freshest, and write down or record the key points of meetings and classes [1]. If the problem continues, your doctor can refer you to a specialist for a more detailed assessment and memory training [2]. To read about talking to your employer and returning to work gradually, see Returning to work and everyday life.
Chemo brain vs dementia: what is the difference?
Many patients worry that forgetfulness after chemotherapy is the start of Alzheimer's disease. The two are different:
- Chemo brain is usually mild, mainly affects memory, concentration and speed of thinking, and in most people eases with time [2, 6]. Problems such as being unable to speak or weakness of an arm and leg on one side are not usually part of chemo brain [2].
- In two large US studies of tens of thousands of older women with breast cancer, those who had chemotherapy did not develop dementia more often than the others in the years that followed [11, 12].
If your forgetfulness is getting worse instead of better, or the people around you notice a big change in your behaviour, see a doctor so that other causes can be checked [2].
When should I call my doctor?
Chemo brain usually comes on gradually and is mild. Talk to your doctor if you have:
- forgetfulness or poor concentration that makes work, study, driving or taking your medicines correctly difficult or unsafe [2, 3]
- forgetfulness that is getting worse instead of better [2]
- sadness, hopelessness or loss of interest on most days, or long-lasting poor sleep [2, 3]
Sudden confusion, sudden difficulty speaking or understanding, weakness or numbness on one side of the body, a seizure or a severe new headache are not usual signs of chemo brain [2]; call your local emergency number straight away. If you have a fever with confusion during chemotherapy, go to the emergency department straight away; read: Fever and warning signs during chemotherapy.
Frequently asked questions
Is forgetfulness during chemotherapy normal?
Is chemo brain permanent?
Is there a tablet or medicine to boost memory for chemo brain?
No medicine has yet been shown to work for it. Several medicines, including an Alzheimer's medicine and stimulant medicines, have been tested in studies, but the results have been mixed; in a large study, the Alzheimer's medicine donepezil did not improve memory [2, 3]. Do not take memory-boosting pills without talking to your doctor.
Do tamoxifen or other hormone tablets cause forgetfulness too?
They may. In some studies tamoxifen was linked with slightly weaker memory, but in one study exemestane tablets had no such effect [2, 3]. In a large study, women who had hormone tablets alone also reported more forgetfulness for several years than before treatment [6]. Do not stop your tablets on your own; if forgetfulness is bothering you, talk to your doctor.
Does chemotherapy cause Alzheimer's disease?
Read more
- What are the side effects of chemotherapy?
- When do chemotherapy side effects start, and how long do they last?
- Fatigue from cancer and its treatment
- Returning to work and everyday life
- Early menopause and hot flushes after cancer treatment
- After cancer treatment ends: follow-up, late effects and feeling normal again
Evidence, assessment and management (for doctors)
For physicians
Prevalence and course. Cancer-related cognitive impairment (CRCI) has been reported in up to 30% of patients before chemotherapy, in up to 75% during treatment (patient-reported) and in up to 35% many years after treatment [4]. In the nationwide prospective NCORP cohort (580 patients with stage I–IIIC breast cancer and 363 controls), visual memory (CANTAB Delayed Match to Sample) declined from before chemotherapy to 6 months after it (P = .005), while controls did not change [5]. In the TAILORx substudy (552 women with RS 11–25), FACT-Cog PCI scores were lower than baseline in both arms at months 3, 6, 12, 24 and 36; the decline was greater with chemoendocrine therapy at months 3 and 6, but the difference was not significant at month 12 and beyond [6]. 196 breast cancer survivors treated with 6 cycles of CMF (on average 21 years earlier) performed worse than 1,509 women from the general population on immediate and delayed verbal memory, processing speed, executive function and psychomotor speed [7]. In lymphoma (73 patients, 75 controls), the decline in RAVLT immediate and delayed recall and verbal fluency compared with controls persisted up to 1 year after chemotherapy [8].
Domains and assessment. In a meta-analysis, effect sizes were −0.27 for executive function, −0.21 for memory and −0.17 for verbal function. Subjective complaints and objective tests often do not agree (only 8 of 24 studies showed a significant correlation). Focal motor or cortical deficits (aphasia, apraxia) are uncommon in CRCI and suggest another cause. Tools: FACT-Cog version 3 and PROMIS (patient-reported); the MMSE has variable sensitivity for mild impairment. Take a focused history (educational attainment, job responsibilities) and review medicines, mood, sleep, pain and fatigue [2].
Interventions. Online cognitive rehabilitation, Insight (242 survivors, 6–60 months after at least 3 cycles of adjuvant chemotherapy; 15 weeks): PCI was lower at the end of the intervention and 6 months later (P < .001); neuropsychological tests did not differ [9]. PAM exercise trial (181 breast cancer patients 2–4 years after diagnosis with cognitive complaints and lower-than-expected test performance; 6 months of supervised aerobic and strength training 2 h/week plus Nordic walking 2 h/week): no difference in the primary outcome (HVLT-R); self-reported cognition, fatigue, quality of life and depression improved [10]. Donepezil (5 mg daily for 6 weeks, then 10 mg for 18 weeks; 276 breast cancer survivors) had no effect on memory or other domains. Seven phase II trials of psychostimulants (methylphenidate, modafinil) had mixed results and were underpowered. Erythropoiesis-stimulating agents had no effect on self-reported cognition and carry cardiovascular and thrombotic risks. With whole-brain radiotherapy, memantine delayed the time to cognitive decline, although the primary endpoint was not significant [2].
Dementia. SEER-Medicare (21,362 women aged 66–80, median follow-up 59 months): adjuvant chemotherapy was not associated with a higher risk of dementia (HR 0.83, 0.74 and 0.49 in the 66–70, 71–75 and 76–80 age groups); the authors suggest that very elderly women who receive chemotherapy may have a lower baseline risk [11]. SEER (62,565 women aged 65 and over, follow-up up to 16 years): no significant association with drug-induced dementia or unspecified cognitive disorders, and the risk of Alzheimer's disease and vascular dementia was lower in the chemotherapy group [12].
Related cancer types
Related questions
References
12 referencesShow all referencesClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
This page is based on reputable scientific sources and was last updated on 28 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
Printed from the website; the full and up-to-date version: https://drdabiri.com/en/questions/chemo-brain/