Obesity and overweight, with or without metabolic dysregulation, pose vexing problems for many patients with mood, anxiety, or psychotic disorders. More than one-half of individuals with severe mental illnesses are obese or overweight,1 resulting from multiple factors that may include psychiatric symptoms (eg, anergia and hyperphagia), poor dietary choices, sedentary lifestyle, underlying inflammatory processes, medical comorbidities, and iatrogenic consequences of certain medications. Unfortunately, numerous psychotropic medications can increase weight and appetite due to a variety of mechanisms, including antihistaminergic effects, direct appetite-stimulating effects, and proclivities to cause insulin resistance. While individual agents can vary, a recent review identified an overall 2-fold increased risk for rapid, significant weight gain during treatment with antipsychotics as a class.2 In addition to lifestyle modifications (diet and exercise), many pharmacologic strategies have been proposed to counter iatrogenic weight gain, including appetite suppressants (eg, pro-dopaminergic agents such as phentermine, stimulants, and amantadine), pro-anorectant anticonvulsants (eg, topiramate or zonisamide), opioid receptor antagonists (eg, olanzapine/samidorphan or naltrexone) and oral hypoglycemics such as metformin. However, the magnitude of impact for most of these agents to reverse iatrogenic weight gain tends to be modest, particularly once significant weight gain (ie, ≥7% of initial body weight) has already occurred.
Pharmacologic strategies to modulate or enhance the effects of insulin hold particular importance for combatting psychotropic-associated weight gain. Insulin transports glucose from the intravascular space to end organs for fuel consumption; to varying degrees, second-generation antipsychotics (SGAs) and some other psychotropic medications can cause insulin resistance. This in turn leads to excessive storage of underutilized glucose in the liver (glycogenesis), the potential for developing fatty liver (ie, nonalcoholic steatohepatitis), and conversion of excess carbohydrates to fatty acids and triglycerides, with subsequent storage in adipose tissue. Medications that can enhance the activity of insulin (so-called incretin mimetics) can help to overcome insulin resistance caused by SGAs (and potentially by other psychotropic medications) and essentially lead to weight loss through enhanced “fuel efficiency.”
Metformin, typically dosed up to 1,000 mg twice daily with meals, has increasingly become recognized as a first-line strategy to attenuate weight gain and glycemic dysregulation from SGAs via its ability to reduce insulin resistance. Yet meta-analyses have shown that although results are significantly better than placebo, overall long-term weight loss from metformin alone tends to be rather modest (<4 kg) and associated with a reduction in body mass index (BMI) of only approximately 1 point.3 Psychiatrists (and other clinicians who prescribe psychotropic medications that can cause weight gain or metabolic dysregulation) therefore need to become familiar with alternative or adjunctive weight loss options. The use of a relatively new class of incretin mimetics called glucagon-like peptide 1 (GLP-1) agonists (Table) has been associated with profound and often dramatic weight loss and improvement of glycemic parameters in patients with obesity and glycemic dysregulation.
What are GLP-1 agonists?
GLP-1 is a hormone secreted by L cells in the intestinal mucosa in response to food. GLP-1 agonists reduce blood sugar by increasing insulin secretion, decreasing glucagon release (thus downregulating further increases in blood sugar), and reducing insulin resistance. GLP-1 agonists also reduce appetite by directly stimulating the satiety center and slowing gastric emptying and GI motility. In addition to GLP-1 agonism, some medications in this family (notably tirzepatide) also agonize a second hormone, glucose-dependent insulinotropic polypeptide, which can further induce insulin secretion as well as decrease stomach acid secretion, potentially delivering an even more substantial reduction in appetite and weight.
Routes of administration and FDA indications
Due to limited bioavailability, most GLP-1 agonists require subcutaneous (SC) injections (the sole exception is the Rybelsus brand of semaglutide, which comes in a daily pill form). Most are FDA-approved not specifically for weight loss but for patients with type 2 diabetes (defined as a hemoglobin A1C ≥6.5% or a fasting blood glucose level ≥126 mg/dL). Weight loss represents a secondary outcome for GLP-1 agonists FDA-approved for glycemic control in patients with type 2 diabetes. The 2 current exceptions to this classification are the Wegovy brand of semaglutide (ie, dosing of 2.4 mg) and the Saxenda brand of liraglutide, both of which carry FDA indications for chronic weight management alone (when paired with dietary and lifestyle modification) in individuals who are obese (BMI >30 kg/m2) regardless of the presence or absence of diabetes, or for persons who are overweight (BMI >27 kg/m2) and have ≥1 weight-related comorbid condition (eg, hypertension, type 2 diabetes, or dyslipidemia). Although patients at risk for diabetes (ie, prediabetes, defined as a hemoglobin A1C 5.7% to 6.4% or a fasting blood glucose level 100 to 125 mg/dL) were included in FDA registration trials of Saxenda or Wegovy, prediabetes is not an FDA indication for any GLP-1 agonist.
Data in weight loss
Most of the existing empirical data on weight loss with GLP-1 agonists come from studies of individuals who are overweight or obese, with or without type 2 diabetes, rather than from studies using these agents to counteract iatrogenic weight gain. In a retrospective cohort study of patients with type 2 diabetes, coadministration with serotonergic antidepressants (eg, citalopram/escitalopram) was associated with attenuation of the weight loss effects of GLP-1 agonists.4
Liraglutide currently is the sole GLP-1 agonist studied for treating SGA-associated weight gain. A 16-week randomized trial compared once-daily SC injected liraglutide vs placebo in patients with schizophrenia who incurred weight gain and prediabetes after taking olanzapine or clozapine.5 Significantly more patients taking liraglutide than placebo developed normal glucose tolerance (64% vs 16%), and body weight decreased by a mean of 5.3 kg.
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