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Guideline: Metformin to Prevent Antipsychotic-Induced Weight Gain

23 Dec, 2024 | 20:55h | UTC

Introduction:
This guideline was developed to address a pressing need for strategies to prevent antipsychotic-induced weight gain (AIWG), a frequent and troubling adverse effect of treatment in individuals with severe mental illness (SMI). Although metformin has shown consistent benefits in mitigating weight gain when initiated alongside antipsychotics, clinical uptake remains limited. The guideline follows the AGREE II framework and synthesizes both randomized and observational research, including Cochrane and meta-analytic data. The primary objective is to outline explicit indications, dosing approaches, and duration for using metformin to avert AIWG.

Key Recommendations:

  1. Co-initiation With High-Risk Agents: In patients requiring higher-risk antipsychotics (olanzapine, clozapine), start metformin simultaneously. Evidence suggests that concurrent treatment may lessen weight gain by 3 to 5 kg in the early months, potentially yielding greater benefits over time.
  2. Co-initiation With Medium-Risk Agents: For individuals prescribed quetiapine, paliperidone, or risperidone who have at least one cardiometabolic risk factor (such as diabetes, prediabetes, hypertension, or BMI above 25) or who are 10 to 25 years old, begin metformin at antipsychotic initiation to curb rapid weight changes.
  3. Initiation During the First Year: If, at any point in the first year of antipsychotic treatment, weight gain exceeds 3% over baseline, consider adding metformin regardless of the antipsychotic being used.
  4. Titration Schedule and Safety: The guideline advises starting at 500 mg once daily, then moving to 500 mg twice daily after about two weeks, with subsequent increases every two weeks up to 1 g twice daily (2 g/day) as tolerated. Metformin must be discontinued if lactic acidosis is suspected, if BMI falls below 20, or if the antipsychotic is stopped. Avoid its use in harmful alcohol consumption.
  5. Additional Treatment Options: In cases of obesity (BMI ≥30) or comorbid metabolic disorders, clinicians should consider adding glucagon-like peptide-1 receptor agonists (GLP-1) where available. If cost, supply, or access is limited, metformin remains a practical alternative.

Conclusion:
This is the first evidence-based guideline focused on preventing AIWG by starting metformin at the time of antipsychotic initiation or upon early weight gain signs. By reducing the magnitude of weight increase, metformin may alleviate health risks tied to obesity, as well as psychological distress and nonadherence to treatment. Implementing the guideline involves continuous weight monitoring, structured dose adjustments, and shared decision-making. Ensuring clear communication about benefits and potential side effects will be crucial for sustaining adherence and improving patient outcomes.

Reference:
Carolan A, Hynes-Ryan C, Agarwal SM, Bourke R, Cullen W, Gaughran F, Hahn MK, Krivoy A, Lally J, Leucht S, et al. Metformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation. Schizophrenia Bulletin. 2024; sbae205.
DOI: https://doi.org/10.1093/schbul/sbae205

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