Irritability rather than depression during interferon treatment is linked to increased tryptophan catabolism.

Objective: Treatment with recombinant interferon is associated with high rates of psychiatric comorbidity. We investigated the relation between catabolism of the essential amino acid tryptophan, being rate-limiting of peripheral and cerebral serotonin formation, and psychiatric symptoms in patients undergoing combination treatment with interferon-alpha and ribavirin.

Patients And Methods: Eighteen patients with viral hepatitis C who received interferon were included. A psychiatrist screened patients before and while on interferon-alpha treatment for 2 months, using a structured diagnostic interview. Fasting plasma tryptophan and platelet serotonin levels were measured at each visit.

Results: At baseline no evident psychopathology was observed. After 2 months of interferon treatment, 10 patients experienced increased irritability. No other structural psychopathology was observed. Decreased plasma tryptophan level correlated with the presence of irritability (p = .047). Platelet serotonin levels were found to be decreased during treatment (p = .002).

Conclusions: Aggressive impulse dysregulation is highly prevalent in patients receiving interferon treatment. This is associated with decreased plasma tryptophan levels which may lead to attenuated peripheral and central serotonergic neurotransmission.