Between 10 and 15 percent of patients find the chronic side effects intolerable and discontinue treatment. Interferon is not thought to readily cross the blood-brain barrier. Severe depression may occur and suicidal ideation is well described. This can be more marked in patients with a history of depression, but suicide has been reported in patients without a previous psychiatric history. They usually regress after discontinuing therapy, albeit after some weeks.
Severe depression is a medical emergency.
The overall incidence of neurotoxicity is 25-33 percent. Seizures have been recorded in 1.3 percent of patients. There are isolated reports of extrapyramidal syndromes with ataxia and akathisia. Paraesthesias have been recorded. Table 1 lists common adverse events associated with interferon alpha in a recent trial, and Table 2 lists a range of laboratory variables.