The rule that is supposed to make anesthesia safe is simple. Stop eating solids eight hours before surgery and your stomach will be empty when the anesthesiologist puts you under. In a group of teenagers taking GLP-1 drugs, that rule failed. Eighty percent of them still had solid food sitting in the stomach, even after fasting for more than twelve hours, well past what the guideline asks.
The finding comes from a prospective cohort study published online September 8 in the British Journal of Anaesthesia ↗. At a single hospital between June 2023 and November 2024, researchers scanned the stomachs of 67 adolescents, ages 10 to 18, before scheduled procedures. They used gastric ultrasound, a bedside scan that looks at the antrum (the lower part of the stomach) to see whether it holds solids or a meaningful volume of fluid. The patients fell into three groups: 20 on a GLP-1 receptor agonist, 27 who were at risk of slow stomach emptying for other reasons but were not on the drugs, and 20 healthy controls.
Everyone had followed the fasting instructions, and then some. The median fast was 13 hours for solids, against a guideline that asks for 8. Despite that, 16 of the 20 adolescents on GLP-1 drugs, or 80 percent, had solid contents on the scan. In the at-risk group it was 17 of 27, or 63 percent. In the healthy controls it was 1 of 20, or 5 percent. The gap held up after the researchers adjusted for age, body mass index, sex, race, and how long each patient had actually fasted (adjusted p less than 0.02). The threshold for a full stomach was concrete: any solids present, or a measured gastric fluid volume of at least 1.5 milliliters per kilogram of body weight.
Why this matters is the reason the fasting rule exists at all. Under general anesthesia the reflexes that keep stomach contents out of the lungs switch off. If the stomach is full, that material can come back up and be inhaled, a complication called aspiration that can cause severe pneumonia or worse. Fasting is the cheap insurance against it, and the whole system assumes that after enough hours the stomach is empty. GLP-1 drugs break that assumption because slowing gastric emptying is part of how they work. By keeping food in the stomach longer, they blunt appetite. The same effect leaves the stomach loaded when the clock says it should be clear.
These drugs are no longer an adults-only concern. GLP-1 receptor agonists are approved from age 10 for type 2 diabetes and from age 12 for obesity, which is exactly the age band this study looked at. The two most likely to be in a teenager's medicine cabinet are semaglutide ↗, sold as Wegovy for weight and Ozempic for diabetes, and liraglutide ↗, sold as Saxenda and Victoza. Both slow the stomach, and the daily and weekly dosing schedules mean a patient showing up for surgery has usually taken a dose within the window where the effect is strongest.
The caveats are real and worth stating. The GLP-1 arm was 20 patients at one institution, which is small. Gastric ultrasound measures retained contents, not aspiration itself, so the study documents the loaded stomach without capturing whether any of these teenagers went on to inhale it. And the at-risk group at 63 percent is a reminder that a full stomach after fasting is not unique to these drugs, though the GLP-1 group had the highest rate of the three. What the controls at 5 percent show is that the fast works as intended in ordinary teenagers. It is the drug, layered on top, that defeats it.
This is the first pediatric-specific read on a problem that has so far been argued mostly in adults. A Canadian Journal of Anesthesia meta-analysis put the adult emptying delay at about 74 minutes on average ↗, and the 2023 advisory from the American Society of Anesthesiologists to consider holding the drugs before surgery was written for adults and extrapolated down to children. The retained-contents signal is now documented in kids too. Whether it translates into actual harm is the question the ultrasound cannot answer, which is why the practical takeaway is narrow and specific: in an adolescent on a GLP-1 drug, the standard fast is not a guarantee, and an anesthesiologist has reason to scan before assuming an empty stomach.