Colonoscopy and Endoscopy on a GLP-1 Microdose: Bowel Prep, Food Left in the Stomach, and Whether to Hold a Dose
A colonoscopy or upper endoscopy on a GLP-1 microdose raises two practical questions: will the bowel prep work, and will the stomach be empty when sedation starts? The studies show GLP-1 users more often arrive with a less clean colon and with food still in the stomach. Pooled data do not show more aspiration, and nobody has studied microdoses directly.
10% vs 4%
INADEQUATE BOWEL PREP IN GLP-1 USERS VS MATCHED NON-USERS, 4876 PAIRS
4.54
ODDS RATIO FOR FOOD LEFT IN THE STOMACH AT ENDOSCOPY IN GLP-1 USERS
0.96
ODDS RATIO FOR ASPIRATION PNEUMONIA, MEANING NO SIGNIFICANT DIFFERENCE
GLP-1 medicines slow the gut. That slowing helps with fullness and blood sugar, but it works against two things an endoscopist needs: a colon that the prep has flushed clean, and a stomach that is empty after an overnight fast.
This article covers what the colonoscopy and endoscopy research shows for people taking a GLP-1 medicine, drawing on large cohort studies of bowel prep, two meta-analyses that reached opposite conclusions, gastric ultrasound studies before surgery, the 2024 multisociety guidance and the Wegovy label. Every study used standard prescribed doses. None measured bowel prep or stomach contents at the sub-label doses used in microdosing protocols, so the findings set an upper bound rather than a precise answer.
Key takeaways
- •In a matched study of 4876 GLP-1 users and 4876 non-users, inadequate bowel prep for colonoscopy occurred in 10% of users versus 4% of non-users (Abu-Freha, Endoscopy, 2025).
- •Two meta-analyses disagree on GLP-1 medicines and bowel prep: one found an odds ratio of 2.10 for inadequate prep, the other 1.00. Both found slightly lower average prep scores in users.
- •Across 23 observational studies and 262,018 patients, GLP-1 users had higher odds of food left in the stomach at endoscopy (odds ratio 4.54) but no significant difference in aspiration pneumonia (odds ratio 0.96).
- •The 2024 multisociety guidance says GLP-1 medicines may be continued before procedures in people without added risk, and suggests a liquid diet for at least 24 hours when slow stomach emptying is a concern.
- •No study has measured bowel prep or stomach contents at GLP-1 microdoses. Tell the procedure team about any GLP-1 use, at any dose.
Is it safe to have a colonoscopy while microdosing a GLP-1?
People taking GLP-1 medicines have colonoscopies and upper endoscopies every day, and the research does not show these drugs make the procedures dangerous. What the research does show is a higher chance of a less useful procedure: a colon that is not clean enough to see small polyps, or food left in the stomach that blocks the view or forces the team to stop.
A colonoscopy on a GLP-1 microdose therefore comes down to preparation and communication. The rest of this article walks through the size of each problem and what the guidance suggests doing about it. The stomach side of the story, including how GLP-1 medicines slow emptying in the first place, is covered in our article on GLP-1 microdosing and gastroparesis.
Do GLP-1 medicines make bowel prep for a colonoscopy worse?
Most cohort studies find that GLP-1 medicines make bowel prep somewhat worse. Yao and colleagues at the Mayo Clinic published one of the first studies in the American Journal of Gastroenterology (2024). Among 446 patients having screening or surveillance colonoscopy, 265 were taking a GLP-1 medicine and 181 had stopped it at least three months earlier.
Bowel prep outcomes, GLP-1 users vs recent past users (% of patients)
Yao R et al., Am J Gastroenterol 2024. Retrospective cohort, 446 patients, one academic center. "Prep score under 5" is a total Boston Bowel Preparation Scale score below 5. Standard doses.
- GLP-1 users
- Controls
A poor prep score (a total Boston Bowel Preparation Scale score under 5) was seen in 15.5% of GLP-1 users versus 6.6% of controls. A repeat colonoscopy for poor prep was needed in 18.9% versus 11.1%. The average prep score was 7.0 in users and 7.5 in controls, a modest gap that still translated into more repeat procedures.
A much larger study by Abu-Freha and colleagues in Endoscopy (2025) matched 4876 GLP-1 users with 4876 controls drawn from 333,648 Israeli patients, balancing age, sex, diabetes, obesity and other conditions.
Inadequate bowel prep, GLP-1 users vs matched controls (% of patients)
Abu-Freha N et al., Endoscopy 2025. Propensity-matched multicenter cohort, 4876 pairs. Standard doses.
- GLP-1 users
- Matched controls
Inadequate prep occurred in 10% of GLP-1 users and 4% of controls. The gap held in people with diabetes (12% versus 5%) and without it (8% versus 3%). That second number matters for anyone using a GLP-1 medicine for weight rather than blood sugar, since diabetes on its own is a known cause of poor prep.
Gala and colleagues reported the same direction across 22 endoscopy units at 18 US sites in Gastrointestinal Endoscopy (2025). In 6235 patients (3344 users and 2891 controls), GLP-1 users were more likely to have inadequate prep even after accounting for diabetes, body mass index, opioid use and other factors. The type of GLP-1 medicine made no significant difference.
Why do the meta-analyses on GLP-1 bowel prep disagree?
The meta-analyses disagree because they pooled different sets of studies, and the effect on prep is small enough that study choice moves the answer. Beran and colleagues, writing in the American Journal of Gastroenterology (2025), pooled 5 studies with 10,833 patients and found an odds ratio of 2.10 for inadequate prep in GLP-1 users.
Pooled odds ratio for inadequate bowel prep, GLP-1 users vs non-users
Beran A et al., Am J Gastroenterol 2025; Ahmed Z et al., Gastrointest Endosc 2026. Dashed line at 1.0 marks no difference.
Ahmed and colleagues, in Gastrointestinal Endoscopy (2026), pooled 6 studies and found no difference in the rate of inadequate prep (odds ratio 1.00, confidence interval 0.73 to 1.37). Their authors concluded they did not recommend stopping GLP-1 medicines before colonoscopy, while noting that more evidence is needed.
The two reviews agree on one thing. Average prep scores were lower in GLP-1 users in both: by 0.34 points in the Beran analysis and 0.36 points in the Ahmed analysis. A fair reading is that GLP-1 medicines nudge prep quality down a little, and that the nudge tips some people over the line into an inadequate prep.
Why is food left in the stomach before an upper endoscopy on a GLP-1?
Food is left in the stomach because GLP-1 medicines slow gastric emptying, so a standard fast may not clear it. Chapman and colleagues compared 84 matched pairs (168 people) having an upper endoscopy (EGD) in Gastrointestinal Endoscopy (2024). Retained gastric contents were found in 13.1% of GLP-1 users versus 4.8% of non-users, with poorer views of the stomach lining and more aborted procedures. No anesthesia-related adverse events occurred.
Food or excess fluid left in the stomach after fasting (% of patients)
Chapman MB et al., Gastrointest Endosc 2024 (seen during EGD, 84 matched pairs). Nersessian RSF et al., Anaesthesia 2024 (gastric ultrasound, semaglutide within 10 days, 220 patients). Vlaeminck N et al., Anaesthesia 2026 (gastric ultrasound, 44 matched pairs, "full stomach"). Standard doses; definitions differ by study.
- GLP-1 users
- Controls
Gastric ultrasound, done just before sedation, finds even more. Nersessian and colleagues scanned 220 patients before elective surgery in Anaesthesia (2024). Increased residual gastric content was found in 40% of those who had taken semaglutide within 10 days and in 3% of those who had not. There were no cases of pulmonary aspiration.
Vlaeminck and colleagues, also in Anaesthesia (2026), tried to remove the obvious confounders by matching 44 semaglutide users to 44 controls of similar age, body mass index and diabetes status. A full stomach was seen in 49% of semaglutide users versus 18% of controls, and solid food in 42% versus 7%. The authors noted the raised risk persisted even after one semaglutide dose had been withheld.
Does food left in the stomach raise aspiration risk during sedation?
Food left in the stomach is the reason for concern, but pooled data have not shown a measurable rise in aspiration. Baig and colleagues pooled 23 observational studies with 262,018 patients in Gastrointestinal Endoscopy (2025).
Pooled odds ratios at GI endoscopy, GLP-1 users vs non-users
Baig MU et al., Gastrointest Endosc 2025. 23 observational studies, 262,018 patients. Dashed line at 1.0 marks no difference.
GLP-1 users had higher odds of residual gastric contents (odds ratio 4.54) and of the endoscopy being stopped early (also 4.54). The odds ratio for aspiration pneumonia was 0.96, a result that shows no significant difference. Singh and colleagues reached a similar result in a separate meta-analysis of 23 studies with 77,152 patients in Gastrointestinal Endoscopy (2025), with an aspiration odds ratio of 0.94. They described retained contents and early stops as overall rare events.
The regulator's view is more cautious. Section 5.10 of the Wegovy prescribing information describes rare postmarketing reports of pulmonary aspiration in people on GLP-1 medicines who had food in the stomach despite following fasting instructions. The label states that available data are insufficient to say whether changing fasting rules or pausing the drug reduces that risk, and tells patients to inform their providers before any planned procedure.
Should you stop a GLP-1 microdose before a colonoscopy or endoscopy?
Most people do not need to stop, according to the current multisociety guidance, but the call belongs to the prescriber and procedure team. In late 2024, five groups (the American Gastroenterological Association, the American Society for Metabolic and Bariatric Surgery, the American Society of Anesthesiologists, the International Society of Perioperative Care of Patients with Obesity and the Society of American Gastrointestinal and Endoscopic Surgeons) published joint guidance led by Kindel and colleagues in Surgical Endoscopy and two sister journals.
The guidance says GLP-1 medicines may be continued in people without an elevated risk of slow emptying. It names the factors that raise that risk: being in the dose escalation phase rather than maintenance, taking a higher dose, using a weekly rather than a daily drug, having GI symptoms such as nausea, vomiting, bloating or constipation, and having another condition that slows the gut, such as gastroparesis. It also warns that holding the drug only because someone has obesity, without one of those factors, could amount to weight bias.
When a hold is chosen, the guidance admits that the right duration is unknown. It suggests following the earlier anesthesiology advice: hold a daily drug on the day of the procedure, and hold a weekly drug for 1 week beforehand. Everyone should still be asked about symptoms on the day. The Vlaeminck finding that full stomachs persisted after one withheld dose is a reminder that a hold reduces the risk without removing it.
Does a microdose change the picture?
A microdose probably sits on the lower risk side of the guidance, but that has not been tested. Two of the guidance's risk factors, higher dose and the escalation phase, point toward a stable low dose being gentler on the stomach. A third, weekly dosing, applies to most microdose protocols, which still use a weekly semaglutide or tirzepatide injection.
No study in this article reported results by dose low enough to say what happens at a fraction of the starting dose. The honest summary is that a microdose may lower the chance of a poor prep or a full stomach, and that the procedure team cannot assume it. Someone who has just stepped up their dose, or who has had nausea or constipation that week, is closer to the higher risk profile the guidance describes, regardless of the absolute dose.
Slower movement lower in the gut, which is what undermines bowel prep, is covered in our article on constipation on a GLP-1 microdose.
How can you prepare for a colonoscopy or endoscopy on a GLP-1 microdose?
The most useful step is telling the endoscopy team about the GLP-1 medicine, including the dose and the day of the last injection, well before the procedure. That gives them time to adjust the prep or diet plan, rather than discovering the issue on the day.
When slow emptying is a concern, the multisociety guidance suggests a liquid diet for at least 24 hours before the procedure, the same step already used before colonoscopy and bariatric surgery. It also notes that point-of-care gastric ultrasound can check the stomach on the day where it is available. In the Baig meta-analysis, residual stomach contents were less common when an upper endoscopy and colonoscopy were done on the same day than with an upper endoscopy alone (odds ratio 0.28), likely because of the liquid diet and prep that precede a colonoscopy.
Report symptoms honestly at check-in. Nausea, vomiting, bloating, fullness or constipation in the days before the procedure are the signals the guidance says should change the plan. A team that knows can switch to a more protective airway approach, or reschedule, instead of stopping halfway through.
The same principles apply to surgery under general anesthesia, which our article on GLP-1 microdosing before surgery and anesthesia covers in more detail.
GLP-1 users more often arrive for colonoscopy with a less clean colon and for endoscopy with food still in the stomach. Pooled data do not show more aspiration. Tell the team about any GLP-1 use, at any dose, and let them set the plan.
Frequently asked questions
Can you have a colonoscopy while microdosing a GLP-1?
Yes, people taking GLP-1 medicines have colonoscopies routinely, and the 2024 multisociety guidance says these drugs may be continued in people without added risk factors. The main problem in studies is a less clean colon, which can mean a repeat procedure. No study has looked at microdoses, so tell the endoscopy team about any GLP-1 use, whatever the dose.
Do GLP-1 medicines affect bowel prep for a colonoscopy?
Most cohort studies say yes. In a matched study of 4876 users and 4876 non-users, inadequate prep occurred in 10% of users versus 4% of non-users. Two meta-analyses disagree on the size of the effect, but both found lower average prep scores in GLP-1 users.
Should I stop my GLP-1 microdose before a colonoscopy?
That is a decision for the prescriber and procedure team, not one to make alone. The multisociety guidance from five specialty groups favours continuing the drug in people without risk factors such as recent dose increases or ongoing GI symptoms. If a hold is chosen for a weekly drug, the guidance suggests holding it a week before.
Why do GLP-1 medicines leave food in the stomach before an endoscopy?
GLP-1 medicines slow how fast the stomach empties, so a standard overnight fast may not clear it. In a gastric ultrasound study, 40% of people who took semaglutide within 10 days of surgery had increased stomach contents, compared with 3% of controls. Retained food can hide the stomach lining or force the procedure to stop.
Is aspiration during sedation more likely on a GLP-1?
Pooled data have not shown a clear rise. A meta-analysis of 23 studies and 262,018 patients found an odds ratio for aspiration pneumonia of 0.96, meaning no significant difference. The Wegovy label still lists rare postmarketing reports of aspiration in people with food left in the stomach despite fasting.
Does a clear liquid diet help on a GLP-1 before a procedure?
The multisociety guidance suggests a liquid diet for at least 24 hours before a procedure when there is concern about slow stomach emptying. That is the same step already used before colonoscopy and bariatric surgery. Trials have not tested whether it fully solves the problem in GLP-1 users.
Is a lower GLP-1 dose safer before an endoscopy?
Possibly, but it has not been studied. The multisociety guidance lists higher doses and the dose escalation phase as factors that raise risk, which suggests a stable low dose sits on the lower risk side. Microdoses are still usually weekly injections, and weekly dosing is itself listed as a risk factor.
Does having an upper endoscopy and colonoscopy on the same day help?
In the Baig meta-analysis, residual stomach contents were less common when an upper endoscopy and colonoscopy were done on the same day than with an upper endoscopy alone, with an odds ratio of 0.28. The likely reason is the clear liquid diet and bowel prep that come before a colonoscopy. This is observational data, not a trial.
Clinical references
- Yao R, Gala KS, Ghusn W, et al. Effect of glucagon-like peptide-1 receptor agonists on bowel preparation for colonoscopy. American Journal of Gastroenterology. 2024. doi:10.14309/ajg.0000000000002564
- Abu-Freha N, Yitzhak A, Shirin H, et al. Glucagon-like peptide-1 receptor agonists significantly affect the quality of bowel preparation for colonoscopy. Endoscopy. 2025. doi:10.1055/a-2419-3875
- Gala K, Tome J, Krall M, et al. Quality of bowel preparation for colonoscopy in patients on glucagon-like peptide-1 receptor agonists. Gastrointestinal Endoscopy. 2025. doi:10.1016/j.gie.2024.11.024
- Beran A, Nayfeh T, Akhras A, et al. Effect of glucagon-like peptide-1 receptor agonists on bowel preparation for colonoscopy: a systematic review and meta-analysis. American Journal of Gastroenterology. 2025. doi:10.14309/ajg.0000000000003362
- Ahmed Z, Iqbal A, Arif SF, et al. Bowel preparation quality in patients using glucagon-like peptide-1 agonists: a systematic review and meta-analysis. Gastrointestinal Endoscopy. 2026. doi:10.1016/j.gie.2025.08.027
- Chapman MB, Norwood DA, Price C, et al. Effects of glucagon-like peptide-1 receptor agonists on gastric mucosal visibility and retained gastric contents during EGD. Gastrointestinal Endoscopy. 2024. doi:10.1016/j.gie.2024.05.012
- Nersessian RSF, da Silva LM, Carvalho MAS, et al. Relationship between residual gastric content and peri-operative semaglutide use assessed by gastric ultrasound: a prospective observational study. Anaesthesia. 2024. doi:10.1111/anae.16454
- Vlaeminck N, Van de Putte P, Dekeyser M, et al. Gastric ultrasound in patients receiving semaglutide: a prospective, multicentre, matched control study. Anaesthesia. 2026. doi:10.1111/anae.70129
- Baig MU, Piazza A, Lahooti A, et al. Glucagon-like peptide-1 receptor agonist use and the risk of residual gastric contents and aspiration in patients undergoing GI endoscopy: a systematic review and a meta-analysis. Gastrointestinal Endoscopy. 2025. doi:10.1016/j.gie.2024.12.019
- Singh S, Rahman SH, Khan N, et al. Effects of glucagon-like peptide-1 receptor agonists on endoscopy outcomes: systematic review and meta-analysis. Gastrointestinal Endoscopy. 2025. doi:10.1016/j.gie.2024.10.011
- Kindel TL, Wang AY, Wadhwa A, et al. Multi-society clinical practice guidance for the safe use of glucagon-like peptide-1 receptor agonists in the perioperative period. Surgical Endoscopy. 2025. doi:10.1007/s00464-024-11263-2
- Novo Nordisk. WEGOVY (semaglutide) injection and tablet, prescribing information. DailyMed. 2026. dailymed.nlm.nih.gov
Medical disclaimer. This article is for general educational and informational purposes only. It is not medical advice and not a substitute for the clinicians responsible for your care or your procedure. Sub-label "microdose" regimens of GLP-1 medicines have not been tested in clinical trials, and no study has measured bowel prep quality or stomach contents at microdoses. Charts show values reported in the cited studies, which used standard doses. Do not start, stop or hold a GLP-1 medicine before a procedure without talking to your prescriber and the procedure team, and follow the prep and fasting instructions they give you.