A Growing Number of Patients Are Showing Up to Colonoscopy Already Behind

Colonoscopy prep has always asked a lot of patients: a restricted diet, a full day cleared for laxatives, and a level of at-home compliance that real-world studies have shown fails 15 to 35% of the time . That problem was already large enough on its own. Now it is colliding with something newer: the rapid rise of GLP-1 medications across the exact age group colonoscopy is meant to screen.

The scale of the shift

Nearly one in five US adults, 18%, has now taken a GLP-1 medication like semaglutide or tirzepatide, and 12% are currently using one, up sharply from 6% just eighteen months earlier. Usage isn't evenly spread across the population. It peaks at ages 50 to 64, where 22% of adults report current use. That is not a coincidental overlap. It is the core window for colorectal cancer screening, now guideline-recommended starting at age 45.

Among adults with diagnosed diabetes, over a quarter, 26.5%, are using an injectable GLP-1, with usage climbing to 33.3% in the 50 to 64 age bracket specifically. This is not a niche patient population anymore. It is a meaningful and fast-growing share of everyone walking into a GI practice for a screening colonoscopy.

Why it matters for prep

GLP-1 medications work in part by slowing gastric and intestinal motility, which is a large part of why patients feel full longer and eat less. "One of the intended effects of GLP-1 agonist medications is to slow down the digestive tract," explains Dr. Swati Patel, a gastroenterologist and associate professor at the University of Colorado Cancer Center. That same mechanism works against bowel prep. Standard prep depends on the digestive tract moving fluid through at a predictable pace to flush the colon clean. When that motility is pharmacologically slowed, prep solutions clear more slowly and less completely, leaving residual material behind.

The clinical data bears this out. A meta-analysis of five studies covering 10,833 patients found that GLP-1 users had more than twice the odds of inadequate bowel preparation compared to non-users within that same study population, 10.6% versus 4.6% (American Journal of Gastroenterology, meta-analysis reported by ACP Gastroenterology Monthly, 2025, https://gastroenterology.acponline.org/archives/2025/02/28/2.htm). That 4.6% baseline is lower than the broader 15 to 35% range cited above because it reflects this specific matched cohort rather than the full range of real-world settings and patient populations, but the relative gap, GLP-1 users failing prep at more than double the rate of otherwise similar patients, is the consistent finding across the literature. A separate matched cohort study of over a thousand patients found similar results: GLP-1 users had 2.6 times the odds of inadequate prep and 3 times the odds of needing a repeat procedure (Cole JL et al., American Journal of Gastroenterology, 2025).

Guidance on how to manage this has also been a moving target. In 2023, the American Society of Anesthesiologists initially recommended holding GLP-1 medications before procedures, up to a full week for weekly-dosed drugs. By late 2024, a multi-society consensus reversed that position, advising against routine holding in favor of individualized, case-by-case decisions between patient and care team (ASA Multi-Society Guidance, 2024). Clinicians are now navigating a genuinely unsettled protocol landscape, weighing aspiration risk against the metabolic risk of interrupting a patient's medication.

The problem underneath the problem

This is where the two issues compound rather than simply add up. Bowel prep was already the single most cited reason patients delay, avoid, or fail to complete colonoscopy, with 71% of patients naming it the worst part of the exam and 55% citing it as the primary deterrent to repeating the exam. It was already an at-home, patient-managed process with a wide failure rate even in patients with no complicating factors. GLP-1 use doesn't introduce a new failure mode. It makes the existing one worse, for a growing share of exactly the patients screening guidelines are trying to reach.

The tools available to address it also ask for more patient effort, not less. The guidance that does exist points toward extended clear-liquid diets or split-dosing, both of which raise the bar on compliance rather than lowering it. That is a difficult ask for a population that already struggles with the standard version of prep.

Colorectal cancer remains one of the most preventable cancers when caught early, and colonoscopy remains the gold standard for catching it. A screening pathway is only as strong as the step patients have to get through to complete it. Right now, that step is getting harder for more people at once, and the clinical field is still working out how to respond.

Zera Medical is one of the companies working to rethink that step entirely, with particular attention to patients, including those on GLP-1 medications, for whom the standard at-home approach has never been reliable enough.

This post is part of an ongoing educational series from Zera Medical on the colorectal cancer screening gap and the preparation experience that shapes it. Zera Medical is developing ZeraFlow™, an investigational clinic-based bowel preparation system currently under FDA regulatory review. ZeraFlow has not been cleared or approved by the U.S. Food and Drug Administration and is not available for commercial distribution or sale.