Schizophrenia BulletinMetformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation

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A comprehensive guideline for using metformin to prevent antipsychotic-induced weight gain (AIWG) has been developed using the AGREE II framework and GRADE methodology. The research provides specific recommendations for co-commencing metformin with antipsychotics, addressing a critical gap in clinical practice for managing one of the most common and distressing side effects of antipsychotic treatment.

Key Points:

• Metformin co-commenced with antipsychotics reduces weight gain by 4.03 kg (95% CI −5.78 kg to −2.28 kg) compared to controls, making it the only pharmacological agent proven effective for AIWG prevention
• Strong recommendations include co-commencing metformin with high-risk antipsychotics (olanzapine/clozapine) and with medium-risk antipsychotics (quetiapine/paliperidone/risperidone) in patients aged 10-25 or with cardiometabolic risk factors
• Initiate metformin when >3% increase in baseline body weight occurs during the first year of antipsychotic treatment
• Start at 500mg twice daily, increase weekly to 1g/day, then fortnightly as tolerated up to 2g/day maximum
• Young age and antipsychotic naivety are key risk factors – children/adolescents experience up to twice the weight gain seen in adults

An estimated three quarters of people with psychosis have co-morbid overweight or obesity. (Australian & New Zealand Journal of Pyschiatry)

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