Olanzapine (OLZ), a commonly prescribed second generation antipsychotic drug, is associated with obesity and metabolic syndrome and may contribute to increased cardiovascular morbidity and mortality. Opioidergic neurotransmission may be implicated in the development of these metabolic disturbances. The objective of this study was to assess the effects of opioid blockade on OLZ-treated patients' metabolic status. Patients with schizophrenia or schizoaffective disorder (n=30) on a stable dose of OLZ were randomized in a double-blind fashion to receive an opioid receptor antagonist, naltrexone (NTX), (n=14) or placebo (n=16). The primary outcome measure was the change in body mass index (BMI) at 12 weeks. Secondary measures included body fat and fat-free mass, along with homeostasis model assessment-estimated insulin resistance (HOMA-IR), plasma lipids and liver function tests (LFTs). There was no significant change in BMI between the treatment arms. However, in comparison to the OLZ + placebo combination, the OLZ + NTX group displayed a significant decrease in the fat and increase in fat-free mass along with a trend towards improvement in HOMA-IR values. There were no significant differences in plasma lipids and LFTs. These findings suggest that addition of NTX to OLZ may attenuate OLZ-induced body fat mass gain. A larger study of longer duration will be needed to confirm these results.
Keywords: Opioid; lipid; liver function tests; metabolic syndrome; metabolism; weight gain.