Why Do So Many People Avoid Colonoscopy? The Prep Problem, Explained

Colonoscopy is one of the most effective tools in preventive medicine. It is the only screening method that can both detect colorectal cancer and remove precancerous polyps in the same visit. Yet millions of eligible adults delay or avoid it entirely. The reason usually isn't the procedure. It's what comes before it.

At Zera Medical, we believe the prep is the problem worth solving. Here is what the research shows, and why we are working to change it.

Is colonoscopy prep really the biggest barrier to screening?

For many patients, it is. Only about 67% of eligible U.S. adults are up to date on colorectal cancer screening, and among adults ages 45 to 49, the newest group recommended for screening, that figure drops to roughly 37%. That gap is not explained by lack of awareness or access. Research consistently points to the bowel preparation, not the procedure, as the part patients dread most and the step that most often stands between them and a completed screening.

Why is bowel prep so hard for patients?

Traditional at-home bowel prep asks patients to manage a demanding, multi-step medical process on their own. Depending on the regimen, that can mean days of dietary restriction, drinking large volumes of laxative solution, hours of urgent bathroom trips, disrupted sleep, dehydration, and nausea. Patients also carry the anxiety of not knowing whether they did it correctly, since prep adequacy is only confirmed once the procedure begins.

For older adults, people with mobility limitations, patients with diabetes or chronic constipation, and those taking GLP-1 medications that slow digestion, the burden is even heavier. These groups experience higher rates of intolerance and incomplete prep, which means the patients who often need screening most are the ones the current prep model serves worst.

Does having a colonoscopy make people less afraid of the next one?

You might expect experience to ease the fear. The research shows the opposite. Patients who have already undergone colonoscopy are significantly more averse to bowel prep than patients who have never done it. In a European population study, the odds of citing prep as the worst part of the exam were 2.49 times higher among people with prior colonoscopy experience.

This matters because colorectal cancer screening is not a one-time event. Guidelines call for repeat colonoscopy on a regular surveillance cycle. When lived experience makes patients more resistant rather than less, every difficult prep today becomes a missed screening tomorrow.

What happens when patients attempt the prep anyway?

Even motivated patients frequently can't complete prep successfully. Across real-world studies, 15% to 35% of colonoscopies are performed with inadequate or suboptimal preparation. When prep falls short, the consequences are real. It impairs the physician's ability to see the colon lining, raises the risk of missed lesions, and often forces a repeat colonoscopy within a year per clinical quality guidelines. For the patient, that means going through the entire experience again.

Why does avoiding colonoscopy carry such a high cost?

Because this is one of the few cancers we can often prevent before it starts. When screening finds and removes a precancerous polyp, a cancer that might have developed never does. That is why the lives-saved math is so striking.

Between 1975 and 2020, an estimated 940,000 colorectal cancer deaths were averted in the United States, and 79% of that reduction was attributable to screening and the removal of precancerous polyps, not to treatment advances. In other words, the single most powerful tool against colorectal cancer is catching it early or stopping it before it begins.

Every avoided or failed screening chips away at that protection. A patient who skips colonoscopy because of the prep, or whose prep was too poor to detect a small lesion, loses the early-detection window that makes this disease so beatable. The barrier is not abstract. It is the difference between a polyp removed during a routine visit and a cancer found later, when it is harder to treat.

Is there a different way to approach colonoscopy prep?

The prep model has remained largely unchanged for decades, even as nearly everything else about colonoscopy has improved. We think that is the real problem, and it is the one we set out to solve.

Our approach moves preparation out of the home entirely and into the clinic, where it can be performed under nursing supervision immediately before the procedure. With ZeraFlow, our clinic-based bowel preparation system, the patient takes a few mild laxative tablets the night before and completes a supervised warm-water cleanse at the clinic just before colonoscopy. In a published clinical study of 125 patients, 89.4% achieved good or excellent bowel preparation, median preparation time was 33 minutes, and there were zero device-related serious adverse events.

ZeraFlow is currently pursuing FDA 510(k) clearance and is not yet available in the United States. But the principle behind it addresses the avoidance problem directly: when preparation becomes a short, supervised clinical step rather than a solo ordeal at home, the single biggest reason patients give for skipping colonoscopy starts to disappear.

The bottom line

Colorectal cancer is highly preventable, and screening works. The barrier standing between millions of patients and that protection is not the colonoscopy itself. It is a preparation process designed decades ago that places the entire burden on the patient. Understanding that barrier is the first step. Fixing it is what drives us.

Better prep. Better procedures.

ZeraFlow is an investigational device under development by Zera Medical LLC and has not been cleared by the FDA. It is not currently available for sale in the United States.