The efficacy of metformin in counteracting olanzapine-induced hyperprolactinemia: an open-label prospective study.

Objectives: Prolactin elevation is a common adverse effect of antipsychotic medications. The study aimed to explore the potential of metformin in managing olanzapine-induced hyperprolactinaemia.

Methods: A prospective study was designed to investigate the changes in prolactin levels over an eight-week metformin treatment. Thirty-one patients with schizophrenia (aged 18-60 years) on a stable dose of olanzapine for at least three months were enrolled. Participants received metformin at 1500 mg/day for eight weeks. Prolactin levels and metabolic parameters were measured at baseline and at weeks 2, 4, 6, and 8.

Results: After eight weeks of metformin intervention, prolactin levels significantly decreased from 39.7 ± 20.0 ng/mL at baseline to 35.7 ± 15.7 ng/mL (p = 0.005) with a moderate effect size (Cohen's d = 0.545). Reductions in prolactin levels correlated positively with baseline prolactin levels (r = 0.72, p < 0.001) and baseline glucose levels (r = 0.47, p = 0.008). Body weight, BMI, insulin level, glucose level, and insulin resistance significantly decreased after metformin treatment.

Conclusion: Although participants experienced mild hyperprolactinaemia, metformin effectively counteracted prolactin elevation and improved metabolic parameters. This study highlights metformin's potential to mitigate antipsychotic-induced adverse effect.