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

Goh KK, Wu TH, Chen CH, Chen PY, Lu ML

International journal of psychiatry in clinical practice, 2025

Abstract

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.

Hyperprolactinaemia and metabolic disturbance are prevalent in patients with schizophrenia under olanzapine treatment.Metformin is an…

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Evidence Hub reads this as a cohort study, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence.

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