As GLP-1 Use Surges, Clinicians Weigh Benefits and Risks

Rates of overweight and obesity have more than doubled in the United States during the last three decades, according to a new analysis. By 2050, it’s anticipated that 213 million adults (age, > 25 years) and 43 million children and adolescents will have overweight or obesity. The results led authors of a study to describe obesity as having reached a “crisis point” requiring urgent action and interventions.

Are glucagon-like peptide 1 receptor agonists (GLP-1 RAs), originally developed and prescribed for diabetes and now approved for weight loss, the answer? 

Their popularity is certainly surging. Between the last 6 months of 2022 vs the last 6 months of 2024, the number of patients prescribed GLP-1 RAs increased by 132.6%. This is also reflected in a shift in public awareness, with a recent survey of US adults finding that 32% of respondents had heard “a lot” about these drugs, up from 19% in 2023.

GLP-1 RAs (including tirzepatide, which targets not only the GLP-1 receptor but also the glucose-dependent insulinotropic polypeptide receptor) have shown efficacy in weight loss. A 2022 review and meta-analysis of 22 trials (17,183 patients) found that 50.2% and 17.5% of those treated with GLP-1 RAs had a ≥ 5% and ≥ 10% weight loss, respectively, compared with placebo. A 2023 review of 41 trials (15,135 patients) found that compared with controls, GLP-1 RAs significantly reduced body weight, body mass index, waist circumference, and waist-to-hip ratio.

“GLP-1 RAs are great medications,” Andres Acosta, MD, PhD, director of the Precision Medicine for Obesity Laboratory, Mayo Clinic, Rochester, Minnesota, told Medscape Medical News. “We’ve been using them for almost two decades. But now there’s excitement about their utility in treating obesity.”

Treating the Four Categories of Obesity 

Daniel Drucker, MD, senior investigator at the Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada, is a pioneer in diabetes treatment and particularly in the development of GLP-1 RAs. Drucker told Medscape Medical News that despite the efficacy and enormous potential of GLP-1 RAs, “we know some people don’t lose much weight when taking these medicines and others don’t feel well and can’t take them.”

The number of individuals who don’t respond to or aren’t able to tolerate GLP-1 RAs “might be small — less than 10% of people who try to take them — but we don’t fully understand the differences in response across different individuals,” Drucker said.

Acosta agreed, adding that it’s “essential for us to identify who will be the best responders, as we do with medications for other conditions, such as cancer and cardiovascular disease.”

Acosta’s group has spent more than a decade engaged in efforts to identify unique characteristics among patients with obesity and has succeeded in identifying four obesity phenotypes.

“What matters in the space of GLP-1 is that using this classification, we can identify the best responders and those who don’t respond.” 

The first phenotype, described as “Hungry Gut” (HG), includes patients with abnormal postprandial satiety. “Although they may be satiated at the end of a meal, they have accelerated gastric emptying and therefore feel hungry between meals and want to keep eating,” he said.

There are also patients who experience abnormal satiety during meals. According to Acosta, these are the patients who will return to the table for second and third helpings. “They don’t feel full and continue to eat more and more in a single sitting” — a phenomenon referred to as “Hungry Brain.”

The third phenotype — “Emotional Hunger” — consists of people who are “hedonic” about food or engage in emotional eating behavior, whereas in the fourth group, people have “an abnormal metabolism in which they don’t burn enough calories. They have an inefficient metabolic rate.” This latter phenomenon is called “Slow Burn.”

Acosta and colleagues randomized 312 patients attending a weight management center to phenotype-guided or non–phenotype-guided treatment with anti-obesity medications (phentermine, phentermine/topiramate, bupropion/naltrexone, lorcaserin, and liraglutide). The phenotype-guided approach was associated with a 1.75-fold greater weight loss after 1 year than the non–phenotype-guided approach (mean weight loss, 15.9% vs 9.0%, respectively).

GLP-1 RAs: Not One-Size-Fits-All

Acosta’s group has developed a genetic test that uses patients’ saliva to identify their obesity phenotype, with the aim of predicting the best responders to GLP-1 RAs. The test, MyPhenome genetic obesity test, is licensed by Acosta’s lab and available through Phenomix Sciences.

Acosta and colleagues presented their findings at the American Gastroenterological Association’s 2024 annual meeting regarding a machine-learning gene risk score (ML-GRS) they developed to predict HG, based on saliva and blood samples. Their genetic studies generated a ML-GRS that classified participants with obesity along a continuum from “HG Positive” (HG+) to “HG Negative” (HG−). Compared with the HG− participants, those who were HG+ had superior total body weight loss with semaglutide at 9 and 12 months. When used to predict response, the ML-GRS had an area under the curve of 0.76 (P = .04) and a positive predictive value of 0.95.

According to Acosta, HG+ patients are “the best responders to the GLP-1 RAs, although we don’t yet understand the mechanism of why they have the phenomenon of abnormal postprandial satiety. It may be an abnormal genetic pathway or abnormal secretion of GLP-1. More studies are needed.”

He noted that GLP-1 RAs “might also be helpful with the second [Hungry Brain] category, but these patients do better with phentermine-topiramate,” as demonstrated in a 2023 study conducted by Acosta and colleagues.

His group has also studied which lifestyle interventions are most effective for each phenotype. “When a unique lifestyle intervention targeting each phenotype was applied, patients lost more weight and had greater metabolic improvement,” he reported.

“Treating obesity no longer needs to be trial-and-error, but should be done using precision medicine because one size doesn’t fit all,” Acosta said.

Concerning Side Effects

The popular media has featured stories about individuals who took GLP-1 RAs for weight loss and experienced serious side effects, including a recent account of a British nurse who died after taking tirzepatide. As reported by the BBC, the nurse’s death certificate listed multiple organ failure, septic shock, and pancreatitis as the immediate causes of death, with the “use of prescribed tirzepatide” recorded as a contributing factor. The report went on to note that there were 23 suspected deaths in the United Kingdom tied to semaglutide since 2019.

Beyond brand-name products, there are also risks associated with GLP-1 RAs manufactured by compounding pharmacies. In early November, CNN reported that compounded semaglutide has been linked to at least 10 deaths. Because of a prior shortage of tirzepatide, the US Food and Drug Administration (FDA) had allowed compounding pharmacies to manufacture the drug. In October, the FDA clarified that it won’t take legal action against compounders, even now that the shortage has been resolved.

A pharmacovigilance study using the FDA Adverse Event Reporting System identified “potential safety signals of increased mortality and serious adverse event reporting” associated with certain GLP-1 Ras — especially in younger patients and women (P

The most common side effects reported with GLP-1 RAs are gastrointestinal events, such as nausea, diarrhea, constipation, and vomiting. Most occur during dose initiation and escalation and wane over the following weeks. However, studies have also reported severe side effects, including a higher risk for pancreatitis, bowel obstruction, and gastroparesis, as well as a significantly higher risk for gallbladder and biliary diseases. In fact, according to one study, patients with diabetes taking GLP-1 RAs reported gastrointestinal-related issues as a “prominent factor” in their decision to discontinue taking these medications.

Several types of cancer are potentially associated with GLP-1 RAs, but findings regarding this potential link have been inconsistent. In a recent review article, Drucker noted there were only inconsistent data linking GLP-1 RAs with thyroid cancer and medullary thyroid cancer and that their potential association with pancreatic has “not been supported by results from randomized controlled trials or real-world data.” 

Concerns have been raised about loss of lean mass and muscle strength and function, especially in older individuals with obesity and advanced liver, cardiovascular, or kidney disease. However, as Drucker pointed out in his review article, muscle function may not correlate with the loss of lean mass. In fact, there are “consistent reductions” in lean mass after bariatric surgery, but “little evidence to date for impairment of muscle function.” He added that newer GLP-1 agents under development for obesity treatment are focusing on “developing complementary therapies that preferentially reduce adipose tissue, while sparing lean mass.”

As covered by Medscape Medical News, there have been reports of potential suicidal ideation associated with GLP-1 RAs. This triggered a 2023 review from the European Medicines Agency. However, recent results from a cohort study and a post hoc analysis of randomized controlled trials concluded that there is no evidence that these drugs increase suicidal ideation or behavior.

In early November, the FDA updated the labels for the GLP-1 RAs to include a warning regarding pulmonary aspiration during general anesthesia or deep sedation. Guidance from a group of societies, led by the American Society of Anesthesiologists, contains recommendations regarding nuances of addressing this concern in surgical patients taking these agents.

Not a Standalone Treatment

Marc-Andre Cornier, MD, professor of medicine, James A. Keating Endowed Chair in Diabetes, and director of the Division of Endocrinology, Diabetes and Metabolic Diseases, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina, told Medscape Medical News that GLP-1 RAs should not be viewed as cosmetic interventions but rather as medical treatments, “not only for weight loss but to reverse obesity-associated complications.” 

Moreover, they should be used “as an adjunct to lifestyle changes,” emphasized Cornier. “We want our patients to have a high-quality diet with high protein content, fluid, vitamins, and minerals, and we want them to exercise.” Especially with the concern of potential loss of muscle mass with these agents, “resistance exercise might help mitigate that concern.”

Recently published recommendations can assist clinicians in guiding patients taking GLP-1 RAs to optimize nutrition. The recommendations note that patients should be referred to a registered dietician to “complement and support” treatment with anti-obesity medications.

What Do Patients Want?

Despite the ever-rising popularity of GLP-1 RAs, a new national survey of over 2200 US adults conducted by the Physicians Committee for Responsible Medicine suggests that most Americans don’t want to use them. Among those who wanted to lose weight, almost three-quarters “disagreed” or “strongly disagreed” with the idea of taking a weight-loss injectable, and 68% of those who wanted to lose weight “agreed” or “strongly agreed” that they would be willing to try a plant-based diet, if it could lead to significant weight loss.

Moreover, many individuals treated with GLP-1 RAs discontinue their use, despite the probability of regaining the weight, according to a report that found only 46.3% of GLP-1 users were still taking the medications at 6 months and only 32.3% at 1 year. The authors commented that their real-world findings show a “substantially lower” 1-year persistence rate, compared with the rate reported in clinical trials. They suggest that the financial burden (> $12,000/year) may contribute to discontinuation.

Discontinuation of GLP-1 RAs can lead to worsening cardiometabolic parameters, with a potential increased risk for adverse outcomes; moreover, weight cycling (“yo-yo dieting”) carries its own risks. In light of these concerns, it’s particularly important to select appropriate patients and to determine whether potential short-term therapy has any enduring benefit.

Acosta agreed. “It’s exciting when looking at the data on how to find the best responders and who should make the effort to take these medications — not only in terms of side effects but also in terms of cost and which patients will receive maximum benefits and should be covered by insurance.” 

Drucker has served as a consultant or speaker for Altimmune, Amgen, AstraZeneca, Arrowhead, Boehringer Ingelheim, Kallyope, Merck Research Laboratories, Novo Nordisk, Pfizer, and Zealand Pharma. He holds nonexercised options in Kallyope. Mount Sinai Hospital receives research support for investigator-initiated studies in the Drucker laboratory from Amgen, Novo Nordisk, Pfizer, and Zealand Pharma.

Gila Therapeutics and Phenomix Sciences have licensed Acosta’s research technologies from University of Florida and Mayo Clinic.

 Acosta received consultant fees in the last 5 years from Rhythm Pharmaceuticals, Gila Therapeutics, Amgen, General Mills, Regeneron Pharmaceuticals, Boehringer Ingelheim, Novo Nordisk, Currax, Nestlé, Phenomix Sciences, Bausch Health, and RareDiseases. He received funding support from the National Institutes of Health, Vivus Pharmaceuticals, Novo Nordisk, Apollo Endosurgery, Satiogen Pharmaceuticals, Spatz Medical, Rhythm Pharmaceuticals, Regeneron Pharmaceuticals, Boehringer Ingelheim, and Novo Nordisk.

In the past, Cornier has served as a consultant for Novo Nordisk.

Batya Swift Yasgur, MA, LSW is a freelance writer with a counseling practice in Teaneck, New Jersey. She is a regular contributor to numerous medical publications, including Medscape Medical News and WebMD, and is the author of several consumer-oriented health books as well as Behind the Burqa: Our Lives in Afghanistan and How We Escaped to Freedom (the memoir of two brave Afghan sisters who told her their story).