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

Prolactin elevation is a common adverse effect of antipsychotic medications. The study aimed to explore the potential of metformin in managing olanzapine-induced hyperprolactinaemia. 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. 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 (<i>p</i> = 0.005) with a moderate effect size (Cohen’s <i>d</i> = 0.545). Reductions in prolactin levels correlated positively with baseline prolactin levels (<i>r</i> = 0.72, <i>p</i> &lt; 0.001) and baseline glucose levels (<i>r</i> = 0.47, <i>p</i> = 0.008). Body weight, BMI, insulin level, glucose level, and insulin resistance significantly decreased after metformin treatment. 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. Hyperprolactinaemia and metabolic disturbance are prevalent in patients with schizophrenia under olanzapine treatment.Metformin is an effective strategy to reduce prolactin levels in olanzapine-treated patients with schizophrenia.Metformin could improve olanzapine-induced metabolic abnormalities in patients with schizophrenia. Hyperprolactinaemia and metabolic disturbance are prevalent in patients with schizophrenia under olanzapine treatment. Metformin is an effective strategy to reduce prolactin levels in olanzapine-treated patients with schizophrenia. Metformin could improve olanzapine-induced metabolic abnormalities in patients with schizophrenia.