"Chemo brain" is a non-medical term. It describes abnormal brain function in people who have been treated with chemotherapy.

The general problem is a decline in memory function or a loss of the ability to concentrate. Certain commonly used chemotherapy will sometimes cause both short- and long-term abnormalities.

When chemotherapy is used alone, these problems may be reversible after the chemotherapy is over. On rare instances, the problems may be permanent. Using radiation alone to the brain area can cause similar problems.

The real problem is the decline of brain function that can occur when chemotherapy and radiation are both used. It is possible that the effects of radiation on the brain may alter the blood vessels of the brain. This allows more chemotherapy to enter the brain and cause damage. In rare cases, the long lasting effects can be devastating.

The decision to use both chemotherapy and radiation therapy in people with cancer is a very important one. The possibility of the loss of brain function has to be weighed against the benefit of this treatment.