Involvement of the endogenous opioid system in the drinking behavior of schizophrenic patients displaying self-induced water intoxication: a double-blind controlled study with naloxone.

Previously we found significant suppression of polydipsia in a schizophrenic patient with PIP syndrome (psychosis, intermittent hyponatremia, and polydipsia). Suppression was obtained with a small dose of naloxone injected once every 2 weeks in long-term repeated studies. We attempted to confirm the effect of naloxone on PIP syndrome by using a double-blind controlled study. The body weights of eight schizophrenic inpatients with PIP syndrome were checked five times daily, and the maximum weight gain during 1 day was chosen as an index of their polydipsia. Naloxone (0.6 mg in three divided doses) or placebo (saline) injection was given once every 2 weeks three times. Assignment to either the naloxone or placebo series was done randomly in a double-blind, crossover design. Naloxone decreased the maximum weight gain per day significantly in five cases. However, naloxone also increased weight gain significantly in three cases. There was no correlation of the weight-increasing effect of naloxone with the duration and intensity of excessive drinking. Our findings showed that the endogenous opioid system might be related to compulsive drinking behavior in the PIP syndrome and that opioid antagonists such as naloxone or naltrexone could be useful in the therapy of PIP syndrome.