Chemobrain refers to a syndrome (a bunch of symptoms) that some people get when they take chemotherapy drugs. Chemotherapy is a systematic treatment, meaning it goes all over the body. An unfortunate side effect of many chemotherapy agents is a diminshment in mental energy and acuity. As a stimulant, modafinil has found some interest from doctors for treatment of this condition.
A recent University of Rochester study showed that modafnil is effective in treatment of chemobrain.
A phase III clinical trial of modafinil on people taking the chemotherapy drug doclataxel found "modest" benefit for the fatigue those patients experience.