Evidence review: Open Peptide Project (verified against primary PubMed, ClinicalTrials.gov & FDA records) · Last checked 2026-10-27. ← Back to Evidence Library

Incretin and GLP-1 drug safety: GI side effects, gallbladder, pancreatitis, lean mass and anesthesia

Name: Incretin and GLP-1 drug safety: GI side effects, gallbladder, pancreatitis, lean mass and anesthesia
Published: 2026-10-27

What the labels and trials say about the most common and the most serious risks of semaglutide, tirzepatide and related drugs

Evidence verdict: Strong for GI effects and gallbladder risk (large RCTs, meta-analysis, FDA labels). Label-based for pancreatitis, thyroid C-cell warnings and aspiration. [1, 2, 3, 4, 5]

Last reviewed: Oct 27, 2026

In 30 seconds

Nausea, diarrhea, vomiting and constipation are the most common side effects. In the pivotal obesity trials they were mostly mild to moderate and concentrated in the dose-escalation period. [1, 2] [Controlled study]
Gallbladder disease is more common: across 76 RCTs, GLP-1 drugs raised the risk of gallbladder or biliary disease, especially at higher doses, with longer use and in weight-loss trials. [3] [Controlled study, meta-analysis]
Labels carry a boxed warning for thyroid C-cell tumors (seen in rodents; human relevance not determined), and warn about acute pancreatitis and pulmonary aspiration under anesthesia. [4, 5] [Regulatory]
A 2024 multisociety guidance says most patients can continue these drugs before elective procedures, with extra precautions for people at higher risk of delayed stomach emptying. Tell your surgical and anesthesia team you take one. [6] [Guidance]

Gastrointestinal effects

In STEP 1 (1,961 adults), nausea and diarrhea were the most common semaglutide side effects. They were typically transient and mild to moderate, and 4.5% of semaglutide versus 0.8% of placebo participants stopped because of GI events. [1] [Controlled study] In SURMOUNT-1, the most common tirzepatide adverse events were gastrointestinal, mostly mild to moderate and occurring mainly during dose escalation. [2] [Controlled study] The Wegovy label warns that use has been associated with GI reactions that are sometimes severe, and says it is not recommended in severe gastroparesis. [4] [Regulatory]

Gallbladder disease

A meta-analysis of 76 RCTs (103,371 patients) found GLP-1 drugs were associated with more gallbladder or biliary disease (relative risk 1.37), including gallstones and gallbladder inflammation. The risk was higher in weight-loss trials, at higher doses and with longer use. [3] [Controlled study, meta-analysis] The Wegovy label reports gallstones in 1.6% of injection-treated adults versus 0.7% on placebo, notes that substantial or rapid weight loss can raise gallbladder risk, and advises gallbladder studies if gallstones are suspected. [4] [Regulatory]

Acute pancreatitis

Labels state that acute pancreatitis, including fatal and non-fatal hemorrhagic or necrotizing pancreatitis, has been observed with GLP-1 receptor agonists. They tell patients to stop the drug and contact their clinician if they have persistent or severe abdominal pain, sometimes radiating to the back, with or without vomiting. [4, 5] [Regulatory]

Thyroid C-cell boxed warning

Semaglutide and tirzepatide caused thyroid C-cell tumors in rodents. Whether they cause medullary thyroid carcinoma (MTC) in humans is unknown, because the human relevance of the rodent tumors has not been determined. Both are contraindicated in people with a personal or family history of MTC or with MEN 2 syndrome. [4, 5] [Regulatory]

Anesthesia, sedation and aspiration

GLP-1 drugs slow stomach emptying. Labels now report rare cases of pulmonary aspiration during general anesthesia or deep sedation in patients who had food left in the stomach despite following fasting instructions. They tell patients to inform clinicians of any planned procedure. [4, 5] [Regulatory] The 2023 ASA consensus has been superseded by a 2024 multisociety guidance from five societies, including ASA, AGA and ASMBS. It recommends shared decision-making. Most patients can continue the drug, and risk is higher in the dose-escalation phase, at higher doses, with weekly dosing, with GI symptoms, or with other conditions that slow the stomach. For higher-risk patients, care teams may use a liquid diet for at least 24 hours beforehand, gastric ultrasound, or a modified anesthesia plan. [6] [Guidance] A newer US multisociety replacement was not found (PubMed searched Oct 27, 2026). Timing decisions belong to the surgical and anesthesia team; this page does not tell anyone when to stop a medicine.

Lean mass loss

A 2026 systematic review of 35 RCTs found a median of about 28% of weight lost on incretin drugs came from muscle-based measures, and no trial measured objective physical function. [7] [Controlled study, review] See the lean-mass guide for details.

Other label warnings

Labels also warn about low blood sugar when combined with insulin or insulin secretagogues, acute kidney injury from dehydration, and serious hypersensitivity reactions. Wegovy should be stopped at least 2 months before a planned pregnancy. [4] [Regulatory] See the interactions guide. Compounded or online versions do not come with these labels, and test purchases of online semaglutide found low purity and endotoxin. [8] [Observational]

Evidence levels used on this page

[Regulatory] FDA, USP or WADA primary document or an FDA-approved label. [Controlled study] randomized trial or systematic review of trials. [Observational] surveillance, pharmacovigilance or cohort data. [Lab] analytical, cell or animal work. [Guidance] professional-society guidance. [Policy] Open Peptide Project published policy.

Semaglutide, Tirzepatide, GLP-1 lean mass loss and muscle preservation, Peptide drug interactions and contraindications

References

Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021. PMID 33567185.
Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022. PMID 35658024.
He L, et al. Association of glucagon-like peptide-1 receptor agonist use with risk of gallbladder and biliary diseases: a systematic review and meta-analysis of randomized clinical trials. JAMA Intern Med. 2022. PMID 35344001.
WEGOVY (semaglutide) injection and tablets, prescribing information, Novo Nordisk (NDA 215256). DailyMed setid ee06186f-2aa3-4990-a760-757579d8f77b, published Jun 30, 2026.
ZEPBOUND (tirzepatide) prescribing information, Eli Lilly (NDA 217806). DailyMed/openFDA setid 487cd7e7-434c-4925-99fa-aa80b1cc776b, effective Aug 28, 2026.
Joshi GP, et al. Preprocedure care of patients on glucagon-like peptide-1 receptor agonists: a multisociety clinical practice guidance. Anesthesiology. 2024. PMID 39471342. Also published as Kindel TL, et al. Surg Obes Relat Dis. 2024. PMID 39482213.
Batsis et al. Effect of incretin-based and nonpharmacologic weight loss on body composition: a systematic review. Ann Intern Med. 2026. PMID 41996180.
Ashraf AR, et al. Multifactor quality and safety analysis of semaglutide products sold by online sellers without a prescription. J Med Internet Res. 2024. PMID 39509151.

Disclaimer: This page is for education only. It is not medical advice, and it does not endorse using, buying or preparing any unapproved product. Talk to a licensed clinician before you start, stop or change any treatment.