Megan Brooks

December 20, 2024

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A new evidence-based guideline recommends prescribing metformin when initiating antipsychotic treatment to help mitigate weight gain in certain instances.

There is “good evidence” that metformin can prevent weight gain caused by antipsychotics, first author Aoife Carolan, MPharm, with Saint John of God Hospital and the Royal College of Surgeons, Dublin, Ireland, told Medscape Medical News.

“While there have been some general recommendations to use metformin for this purpose, until now, clear guidance on how to prevent this side effect of treatment has been lacking,” Carolan told Medscape Medical News.

“At present, it is likely that metformin is underused and when used, it is likely to be started after the weight gain occurs. Therefore, this guideline will reflect a new practice for most clinicians,” Carolan added.

The guideline was published online on December 9 in Schizophrenia Bulletin.

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It offers three key recommendations:

• Initiate metformin when prescribing a high-risk weight-inducing antipsychotic, such as olanzapine or clozapine.
• Initiate metformin with a medium-risk antipsychotic (quetiapine, paliperidone, or risperidone) in patients with one or more cardiometabolic risk factors; in patients aged 10-25 years; or in patients with a body mass index (BMI) between 25 and 30.
• Initiate metformin with any antipsychotic if > 3% increase in baseline body weight is observed during the first 12 months of treatment.

The guideline authors noted that a recent Cochrane review of pharmacological interventions for the prevention of antipsychotic-induced weight gain showed that metformin is the only pharmacological agent that may be effective for preventing weight gain.

The review showed that starting metformin with antipsychotic medicines can reduce the extent of weight gain by 4.03 kg compared with controls.

In terms of dose, the guideline recommends escalating from 500 mg daily to 500 mg twice daily over 2 weeks, followed by biweekly increases of 500 mg as tolerated up to 1 g twice daily at week 6.

Metformin should be discontinued if risks for lactic acidosis are present, or the condition is suspected; if BMI falls below 20; or if the antipsychotic medicine is discontinued. Metformin should be avoided where there is harmful use of alcohol.

While the guideline focused on metformin, it also recommends that, if available, glucagon-like peptide 1 (GLP-1) agonists, should be considered for patients with a BMI > 30, certain cardiometabolic diseases, or obstructive sleep apnea.

“At present, there is insufficient evidence for the risk benefit calculation for GLP-1 agonists as a preventative agent, but we will continue to monitor the evidence and update the guideline if it is needed,” Carolan told Medscape Medical News.

Experts Weigh In

Medscape Medical News asked several psychiatrists not involved in the guideline development for their thoughts on it.

Ipsit Vahia, MD, McLean Hospital, Belmont, Massachusetts, and Harvard Medical School, Boston, said, “There is an urgent need for evidence to guide treatments that can mitigate the metabolic side effects of antipsychotics.”

While metformin has shown some potential based on preliminary studies, this paper offers more substantial evidence to guide clinicians in using these medications and marks a significant step forward in clinical psychiatry. Vahia told Medscape Medical News.

Lynn DeLisi, MD, also with Harvard Medical School, emphasized that decisions about the use of metformin in patients taking antipsychotics should be made on an individual basis.

“It should not be used routinely with all antipsychotics, as metformin has its own set of side effects,” said DeLisi.

Xiaoduo Fan, MD, MPH, with UMass Chan Medical School, Worcester, Massachusetts, director of UMass MIND, noted thatthe evidence regarding metformin’s benefits to prevent or mitigate antipsychotic-induced weight gain and other metabolic disturbances is clear.

“It was somewhat controversial when psychiatrists started to prescribe metformin 15-20 years ago, but now many psychiatrists feel comfortable doing so. In many clinical settings, especially in academically affiliated hospitals, using metformin to address antipsychotic-associated metabolic concerns has become part of the routine practice,” said Fan.

“The guideline recommendations are generally consistent with what we have been doing clinically. The publication of the guideline may help promote wider use of metformin in the patient population we serve,” Fan added.

Fan also noted that a growing body of the literature has demonstrated the weight loss effect and other metabolic benefits of GLP-1 agonists. “Compared with metformin, GLP-1 agonists are more effective in inducing weight loss and mitigating cardiometabolic risks,” he said.

Fan said his group has completed a double-blind, placebo-controlled trial of 6-month weekly injection of the GLP-1 receptor agonist exenatide, as an adjunctive treatment in 70 patients with schizophrenia. “Preliminary data analysis suggests positive metabolic benefits,” he reported.

This research had no commercial funding. Carolan had no relevant disclosures. A complete list of disclosures for the guideline authors is available with the original article. DeLisi had no relevant disclosures. Fan had received research support from Alkermes; Eli Lilly; Janssen; Otsuka Pharmaceutical Co., Ltd.; Roche; Lundbeck; Boehringer Ingelheim; Neurocrine Biosciences; Intra-Cellular Therapies; Teva; and Bristol Myers Squibb. He served on the BMJ Best Practice’s US Advisory Panel and as the contributor for the BMJ Best Practice — Schizophrenia Topic. Vahia had served as a consultant for Otsuka.

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