Weight gain is a known side effect of many antipsychotic medications, which are used to treat mental illness such as schizophrenia and bipolar affective disorder. In 2020 and 2022, our Canadian Obesity Clinical Practice Guidelines identified the importance of metformin use for prevention of weight gain from antipsychotic medications (see here and here). A new guideline published in Schizophrenia Bulletin provides important updates on this topic.
They point out that:
- Eight out of 10 people will experience antipsychotic-induced weight gain
- Low BMI and healthy range BMI people are at a higher risk of weight gain
- Choice of antipsychotic medication is the most important factor to predict weight gain
They stress the importance of starting metformin in the appropriate patient at the same time that antipsychotic medication is prescribed, when:
- high risk antipsychotic medication is prescribed (eg olanzapine, clozapine)
- medium risk antipsychotic medication is prescribed (eg quetiapine, risperidone, paliperidone) in people with metabolic risk factors, or if >3% weight gain is experienced in the first year of treatment
- lower risk antipsychotic medications (all others) if >3% weight gain is experienced in the first year of treatment
To avoid hesistancy to treat obesity in people living with severe mental illness, though outside of the scope of their guideline, they recommend choosing a GLP1 receptor agonist first in people with BMI ≥30 or ≥27 with metabolic risk factors, and if unavailable, start metformin.
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