GLP-1 receptor agonists and functional gastrointestinal obstruction: mechanistic rationale, emerging evidence, and clinical implications

Dear Editor, Glucagon-like peptide-1 (GLP-1) receptor agonists, such as semaglutide (Ozempic®), represent a major therapeutic advancement in the management of type 2 diabetes mellitus and obesity. These agents produce substantial reductions in HbA1c and body weight while also conferring cardiovascular and nephroprotective benefits1. A well-characterized pharmacodynamic effect of this drug class is delayed gastric emptying, which contributes to improved postprandial glycemic control1. However, increasing clinical attention has focused on whether this physiological effect may, in rare cases, progress to clinically significant gastrointestinal hypomotility. Quantitative assessments of gastric emptying using scintigraphy, stable isotope breath testing, and acetaminophen absorption assays consistently demonstrate delayed gastric emptying with GLP-1 receptor agonists1,2. A systematic review of 15 studies reported a pooled mean delay in gastric half-emptying time of approximately 36 minutes by scintigraphy compared with placebo2. In controlled settings, half-emptying times for solids and liquids have been reported to increase up to 3.4-fold, with significantly greater intragastric retention at 120 and 240 minutes1–3. Although the magnitude of delay varies depending on methodology and meal composition, these findings establish delayed gastric emptying as a reproducible and quantifiable class effect. Mechanistically, GLP-1 receptors are expressed within the myenteric plexus of the enteric nervous system. Receptor activation couples to the Gsα subunit, stimulating adenylyl cyclase and increasing intracellular cyclic adenosine monophosphate (cAMP), thereby enhancing nitrergic transmission via nitric oxide (NO) and modulating vagal efferent pathways1,3. Animal studies demonstrate suppression of fed-state antral contractility, increased pyloric tone, and attenuation of duodenojejunal propulsive activity following GLP-1 administration3. Emerging evidence also suggests functional interaction between enteric neurons and interstitial cells of Cajal, potentially amplifying inhibitory neuromuscular signaling1,3. Collectively, these data provide biological plausibility for GLP-1-associated hypomotility through a cAMP-NO-dependent neuronal mechanism, although the precise segmental contributions across the gastrointestinal tract remain incompletely defined. While delayed gastric emptying is generally dose-dependent and clinically manageable, emerging safety concerns have prompted regulatory scrutiny. In September 2023, the U.S. Food and Drug Administration updated the semaglutide prescribing information to include ileus as a postmarketing adverse reaction. Gastrointestinal adverse effects such as nausea, vomiting, diarrhea, and constipation are common and typically transient4. However, postmarketing pharmacovigilance analyses and regulatory safety reports have identified rare cases of ileus and intestinal obstruction associated with GLP-1 receptor agonists, prompting labeling updates and ongoing safety evaluation5. Although the absolute incidence appears low relative to widespread use, these reports highlight the potential for severe gastrointestinal hypomotility in susceptible individuals. It is important to note that the inhibitory effect of GLP-1 receptor agonists on gastric emptying exhibits partial tachyphylaxis over time. Several studies indicate that delayed gastric emptying diminishes after 4–12 weeks of continuous therapy, reducing the risk of persistent functional obstruction while still achieving postprandial glycemic benefits1,2. Clinicians should consider this temporal pattern when evaluating gastrointestinal risk, particularly in patients with preexisting motility disorders, prior abdominal surgery, or those undergoing surgical or endoscopic procedures. Several patient characteristics may increase susceptibility to GLP-1 receptor agonist-related gastrointestinal hypomotility. These risk factors are summarized in Table 1, which highlights mechanistic rationale and practical considerations to aid clinical decision-making. Table 1 - Patient characteristics and risk factors for GLP-1 receptor agonist-associated gastrointestinal hypomotility. Patient characteristic Mechanistic/clinical Rationale Practical considerations References Older age (>65 years) Reduced baseline gastric motility and slower GI transit Monitor for early symptoms of nausea, vomiting, or bloating; consider slower dose titration 6–10 Prior abdominal surgery or adhesions Altered intestinal anatomy may predispose to obstruction or functional ileus Review surgical history; assess for adhesions; monitor post-dose initiation 6–10 Rapid dose escalation Exacerbates dose-dependent delayed gastric emptying Follow recommended titration schedule; avoid accelerated dosing 1–3,8 Baseline autonomic neuropathy (e.g., long-standing diabetes) Impaired vagal signaling slows gastric emptying Screen for gastroparesis; consider slower titration and close symptom monitoring 1,3,8 Comorbid gastrointestinal conditions (chronic constipation, GERD, hiatal hernia) Baseline motility impairment increases risk of functional obstruction Assess for existing GI symptoms; optimize bowel habits and GI management 6–10 Published case reports reveal a consistent clinical pattern. Symptom onset typically occurs within 4–6 weeks of treatment initiation or dose escalation and is characterized by abdominal pain, distension, nausea, and vomiting. Imaging commonly demonstrates dilated bowel loops without mechanical obstruction, consistent with functional obstruction or pseudo-obstruction6–9. In most cases, conservative management and discontinuation of semaglutide result in symptom resolution without surgical intervention. Notably, many affected individuals had potential predisposing factors, including prior abdominal surgery, adhesions, previous bowel obstruction, or rapid dose escalation. These observations suggest that GLP-1 receptor agonists may not independently cause obstruction but may exacerbate underlying susceptibility to dysmotility. Patients with long-standing diabetes frequently exhibit baseline delayed gastric emptying secondary to autonomic neuropathy. Comorbid conditions such as gastroesophageal reflux disease, chronic constipation, hiatal hernia, or prior gastrointestinal surgery may further impair baseline motility10. In such contexts, pharmacologically induced suppression of antral contractility and increased pyloric tone may shift the balance toward clinically significant hypomotility. Additionally, unsupervised use or accelerated dose escalation may increase risk. Importantly, the current evidence base consists largely of case reports and pharmacovigilance data, both of which are subject to reporting bias and lack denominator data necessary to estimate true incidence. Large randomized controlled trials evaluating cardiovascular and renal outcomes have not demonstrated a clear signal for intestinal obstruction; however, rare adverse events may be underdetected in such trials. Therefore, while mechanistic plausibility and temporal association support a potential relationship, causality has not been definitively established. From a clinical perspective, these findings underscore the importance of individualized risk assessment. Gradual dose titration, careful evaluation of prior gastrointestinal history, and heightened vigilance in patients with preexisting motility disorders or extensive surgical history may mitigate risk. Awareness of delayed gastric emptying is also relevant in perioperative and procedural settings, where increased residual gastric contents may elevate aspiration risk2–4. This article aligns with the TITAN guidelines on transparency in AI use in health care.11 In summary, semaglutide and other GLP-1 receptor agonists remain cornerstone therapies in diabetes and obesity management due to their substantial metabolic, cardiovascular, and renal benefits. Their established inhibitory effects on gastrointestinal motility, while generally well tolerated, may rarely manifest as clinically significant hypomotility or functional obstruction in susceptible individuals. Further prospective studies are needed to clarify incidence, identify high-risk populations, and better characterize the segmental gastrointestinal effects of chronic GLP-1 receptor activation.