Mental Difficulties Can Persist Long After Chemo. Cognitive dysfunction, long recognized as a sequela of cancer chemotherapy, persists, perhaps indefinitely. It is difficult to sort out to what extent it is a toxic effect of the chemotherapy agents and to what extent an effect of other medications, the cancer patient’s emotional state, sleep disturbance or age-related changes. A decline may be attributed to the chemo by patient or caregivers even if this is not accurate. Reuters Health