Such drugs, injected weekly, mimic a hormone produced in the intestines after meals, called glucagon-like peptide-1 (GLP-1). It helps regulate appetite and food intake, according to the U.S. Food and Drug Administration. The agency approved Wegovy in 2021 for weight management in adults with obesity, Type 2 diabetes, and/or high cholesterol. It’s intended to be used in conjunction with dieting and exercise. The FDA approved Ozempic as a treatment for Type 2 diabetes in 2017.

While the drugs are widely reported as safe, they’re generally only studied in patients for up to a year. Beyond that time, the risk of intestinal obstruction—a potentially fatal condition that requires surgery—continues to increase in Type 2 diabetics, peaking around a year and a half, researchers from China wrote in a recent letter to the editor published in medical journal Acta Pharmaceutical Sinica B.

They cited, among other sources, a 2022 study in Clinical Pharmacology & Therapeutics. It noted that drugs mimicking GLP-1 lead to increased insulin secretion, helpful in lowering blood glucose levels, but can also reduce gastrointestinal motility, leading to constipation—and, thus, potential intestinal obstruction.

GLP-1 may cause “continuous increases in intestinal length,” authors of the new article wrote, causing the small intestine to “become as inelastic and fibrotic as a loose spring.”

“Unfortunately, clinical trials carried out so far have not shown such changes in the human gut,” in part because “it is difficult to determine the length of the small intestine in adults,” they said.

“Since intestinal obstruction is a fatal condition that requires surgery, clinicians should be aware that the emergence of chronic adverse events” in patients on such drugs “may involve the small intestine,” they added.

Nearly three-quarters of American adults are obese or overweight, according to the FDA.

Spurred by use of the drug among celebrities like Elon Musk, demand for Wegovy—which helps overweight patients lose about 15% of their body weight—is surging. Manufacturer Novo Nordisk expects operating profits to rise by nearly 20% this year, propelled in part by sales of the drug, Bloomberg recently reported.