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Post-chemotherapy cognitive impairment (also known as chemotherapy-induced cognitive dysfunction or, colloquially, as chemo brain or chemo fog) describes the cognitive impairment that can result from chemotherapy treatment. Approximately 20-30% of people who undergo chemotherapy experience some level of post-chemotherapy cognitive impairment. The phenomenon first came to light because of the large number of breast cancer survivors who complained of changes in memory, fluency, and other cognitive abilities that impeded their ability to function as they had pre-chemotherapy.[1]


Although the causes (and indeed, existence) of post-chemotherapy cognitive impairment have been a subject of debate, recent studies have confirmed that post-chemotherapy cognitive impairment is a real, measurable side-effect of chemotherapy treatment, at least in some patients.[2] A University of California, Los Angeles study published in October 2006 showed that the brains of breast cancer survivors who were treated with chemotherapy have to work harder to perform tasks than survivors whose treatment was surgical. Even more recently, Japanese researchers have demonstrated that a year after treatment, the brains of cancer survivors treated with chemotherapy had physically shrunk; those of people not treated with chemotherapy had not.[3]

Post-chemotherapy cognitive impairment comes as a surprise to many cancer survivors. Often, survivors think their lives will return to normal when the cancer is gone, only to find that the lingering effects of post-chemotherapy cognitive impairment impede their efforts. Working, connecting with loved ones, carrying out day-to-day tasks—all can be very challenging for an impaired brain. Although post-chemotherapy cognitive impairment appears to be temporary, it can be quite long-lived, with some cases lasting 10 years or more.[4]


To date, most people who experience post-chemotherapy cognitive impairment have had to live with it until it (hopefully) dissipates over time. The Mayo Clinic lists several suggestions for coping with post-chemotherapy cognitive impairment, from exercising your body to taking notes that can help guide you through the day.

There may be good news on the treatment front, however. Very recently, anecdotal evidence has begun to suggest that certain plasticity-based brain training programs may reduce the effects of post-chemotherapy cognitive impairment. At least one clinical study is underway at Posit Science. Other companies are also exploring the field.

One study was done of patients 10 years after chemotherapy, which found post-chemotherapy cognitive impairment persists for the affected subgroup.[How to reference and link to summary or text] No study has found that long-term post-chemotherapy cognitive impairment disappears after 10 years, but that is simply the longest post-chemo period studied to date. Organic nerve damage, one suspected root cause of the condition[How to reference and link to summary or text], is not generally believed to repair itself. Research into treatments is ongoing but is at an early stage.

The drug Provigil, modafinil, approved for narcolepsy has been used off-label in trials with people with symptoms of chemobrain. Modafinil is a wakefulness promoting agent that can improve alertness and concentration.[5] A University of Rochester study of 68 subjects had significant results. "We knew from previous studies that modafinil does alleviate problems with memory and attention, and were hoping it would do the same for breast-cancer patients experiencing chemo-brain, which it did," related the study's lead author Sadhna Kohli, Ph.D, a research assistant professor at the University of Rochester's James P. Wilmot Cancer Center.[6]


  1. Tannock IF, Ahles TA, Ganz PA, Van Dam FS (2004). Cognitive impairment associated with chemotherapy for cancer: report of a workshop. J. Clin. Oncol. 22 (11): 2233-9.
  2. Hede K (2008). Chemobrain is real but may need new name. J. Natl. Cancer Inst. 100 (3): 162-3, 169.
  3. Inagaki M, Yoshikawa E, Matsuoka Y, et al (2007). Smaller regional volumes of brain gray and white matter demonstrated in breast cancer survivors exposed to adjuvant chemotherapy. Cancer 109 (1): 146-56.
  4. Silverman DH, Dy CJ, Castellon SA, et al (2007). Altered frontocortical, cerebellar, and basal ganglia activity in adjuvant-treated breast cancer survivors 5-10 years after chemotherapy. Breast Cancer Res. Treat. 103 (3): 303-11.
  5. Doctors are finding it harder to deny "Chemobrain"The Virginian-Pilot © October 2, 2007
  6. Modafinil Relieves Cognitive Chemotherapy Side Effects Psychiatric News, Stephanie Whyche, August 3, 2007 Volume 42 Number 15, page 31


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