Interferon alpha is a cytokine with antiviral and antineoplastic action, which is commonly used for treatment of Hepatitis C and B, malignant melanoma, Kaposi's sarcoma, kidney cancer and certain hematologic diseases. It is well-known some of its neuropsychiatric symptoms such as depressive symptoms, cognitive impairment, chronic fatigue, dysphoria and anxiety, but there are also other less common like mania, psychotic symptoms and suicide risk that have been reported. These symptoms interfere in the quality of life very significantly, which at the end can affect treatment adherence.

We report a case of a 33-year-old man who was taken to the emergency department by his family referring nervousness, irritability, verbose, and insomnia during the last 5 days. The patient had not psychiatric history. He was diagnosed with a malignant melanoma stage III A a year ago which required to start interferon alpha treatment.

Patient and family tell that symptoms began after forgetting last interferon dose. In the psychopathology exploration, we could observe mood lability, delusion ideas of prosecution, which includes his entire family and autorreferentiality. In the emergency room the blood test, urine drug test and CT were normal.

During the admission, and in collaboration with the Oncology service, it was agreed the reintroduction and maintenance of interferon combined with olanzapine up to 30mg/day and clonazepam up to 6mg/day, which resulted in the resolution of symptoms in two weeks.