Weight gain associated with metformin
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Metformin and Weight Gain: Key Insights
Metformin for Antipsychotic-Induced Weight Gain
Multiple studies show that metformin is effective in reducing or preventing weight gain caused by antipsychotic medications. Meta-analyses and randomized controlled trials consistently report that metformin leads to significant reductions in body weight, body mass index (BMI), and other metabolic parameters compared to placebo in both adults and children taking antipsychotics 1234+3 MORE. The average weight reduction ranges from about 3 to 4.5 kg, and improvements are also seen in insulin resistance and cholesterol levels 1258.
Metformin in Children and Adolescents
In children and adolescents treated with second-generation antipsychotics, metformin has been shown to stabilize or reduce weight gain, lower BMI z-scores, and improve insulin sensitivity 23410. These effects are observed within 12–16 weeks of treatment. Metformin is generally well tolerated, though gastrointestinal side effects like nausea and diarrhea are more common compared to placebo 23410.
Timing and Prevention
Starting metformin at the same time as antipsychotic therapy (co-commencement) is effective in preventing initial weight gain and metabolic disturbances. This approach leads to clinically meaningful reductions in weight and improvements in metabolic health, regardless of whether patients are new to antipsychotics or switching medications .
Dose and Duration Effects
The weight-reducing effect of metformin is more closely related to the duration of treatment rather than the dose, with longer treatment leading to greater weight loss. The maximal effect in patients with antipsychotic-induced weight gain is about 8.8% reduction from baseline weight, typically achieved over several months .
Metformin and Weight Gain in Pregnancy
In pregnant women, especially those with obesity or diabetes, metformin is associated with less excessive weight gain and a higher rate of weight loss compared to those not taking metformin. Importantly, there is no increase in adverse outcomes for the baby, such as fetal growth restriction or low birth weight 79.
Safety and Tolerability
Metformin is generally safe for use in these populations, with the most common side effects being mild gastrointestinal symptoms. Serious adverse events are rare, and the rate of discontinuation due to side effects is similar to placebo 1234+2 MORE.
Conclusion
Metformin is effective in reducing or preventing weight gain associated with antipsychotic medications in both adults and children, and it also helps limit excessive weight gain in pregnancy. Its benefits include improved metabolic health and a good safety profile, though mild gastrointestinal side effects are common. These findings support the use of metformin as a reasonable option for managing medication-related weight gain.
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