Several categories of medications need to be stopped or adjusted before a colonoscopy, and the timelines vary from a week beforehand to the morning of the procedure. Blood thinners, certain diabetes drugs, iron supplements, anti-inflammatory painkillers, some herbal supplements, and fiber products all require changes. Your endoscopy team should give you personalized instructions, but here’s what to expect and why each category matters.
Blood Thinners and Antiplatelet Drugs
Blood thinners carry the most serious risk during a colonoscopy because the doctor may need to remove polyps, and thinned blood makes it harder to stop bleeding at the removal site. Each medication has a different stop time based on how long it stays active in your body.
Clopidogrel (Plavix) should be stopped 7 days before the procedure. Warfarin (Coumadin) is typically held 5 days before, then resumed the day of the procedure once the doctor confirms there’s no bleeding. Newer blood thinners like rivaroxaban (Xarelto) and apixaban (Eliquis) clear the body faster and are usually stopped just 1 to 2 days beforehand, with resumption the day after.
If you take any blood thinner, your gastroenterologist and the doctor who prescribed the medication both need to weigh in. Some people on blood thinners for heart valve replacements or recent blood clots may need a temporary injectable substitute to stay protected while the oral medication is out of their system. Never stop a blood thinner on your own without confirming the plan with your care team.
NSAIDs and Over-the-Counter Pain Relievers
Ibuprofen (Motrin, Advil), naproxen (Aleve), and similar anti-inflammatory painkillers should be stopped 7 days before a colonoscopy. These drugs interfere with platelet function, which can increase minor bleeding if polyps are removed. In one study of nearly 700 patients, minor self-limited bleeding occurred in about 6% of those taking NSAIDs compared to 2% in those who weren’t. Major bleeding requiring treatment was rare in both groups (under 1%), but most endoscopy centers still prefer you stop these medications to minimize any added risk.
If no doctor has specifically recommended daily aspirin for heart protection, you should also stop aspirin 7 days before. If you do take aspirin because a cardiologist prescribed it, ask both your cardiologist and your gastroenterologist whether to hold it. Many doctors allow low-dose aspirin to continue because the heart protection outweighs the small bleeding risk. For pain relief during the week before your colonoscopy, acetaminophen (Tylenol) is generally considered safe to use instead.
Iron Supplements
Stop iron supplements 5 days before your colonoscopy. Iron turns stool dark brown or black and can coat the lining of the colon, making it significantly harder for the doctor to see the tissue clearly. Memorial Sloan Kettering Cancer Center recommends a full 5-day washout period. This applies to standalone iron pills and to multivitamins that contain iron. Check the label on your multivitamin; if it lists iron as an ingredient, switch to one without iron or skip it for the 5 days leading up to your procedure.
Diabetes Medications
Because you’ll be on a clear liquid diet before the colonoscopy, your blood sugar management changes substantially. The adjustments depend on the type of medication.
Metformin should be stopped once you begin the clear liquid diet (usually the day before the procedure) and resumed once you’re eating normal meals again. Since metformin works alongside food intake, taking it while fasting on clear liquids serves little purpose and can increase the risk of side effects.
Rapid-acting insulin (taken before meals) should be cut to 50% of the usual fixed dose once the clear liquid diet starts. If you normally dose based on carbohydrate counting, you can continue that approach since you’ll simply be eating fewer carbs. On the morning of the procedure, rapid-acting insulin is held entirely and resumed when meals resume.
Long-acting (basal) insulin is handled differently. First-generation basal insulins like glargine (Lantus) and detemir (Levemir) can be continued normally the day before, but the morning of the procedure, take only 50% of your usual dose. Second-generation basal insulins like glargine U300 (Toujeo) and degludec (Tresiba) require a reduction to 50% for people with type 2 diabetes, or 50 to 80% for people with type 1, both the day before and the morning of the procedure.
GLP-1 Medications
GLP-1 drugs like semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) slow stomach emptying, which raises the concern that food could remain in the stomach during sedation and increase the risk of aspiration. Updated multi-society guidance from the American Society of Anesthesiologists and several gastroenterology organizations says most patients can continue their GLP-1 medications before elective procedures, but those at highest risk need extra precautions.
You’re considered higher risk if you’re in the early escalation phase of treatment (the first four to eight weeks when doses are being gradually increased), if you’re on a higher dose, or if you’re experiencing GI side effects like nausea, vomiting, or constipation. In those situations, the guidance recommends following a liquid-only diet for 24 hours before the procedure. If you’re still having active GI symptoms, the procedure may be postponed until they resolve. Patients who have been on a stable dose without GI symptoms are generally cleared to continue their medication as scheduled.
Blood Pressure Medications
Most blood pressure medications should be continued as normal leading up to the colonoscopy, but two categories require caution on the morning of the procedure. ACE inhibitors (drugs ending in “-pril,” like lisinopril) and ARBs (drugs ending in “-sartan,” like losartan) can increase the risk of a significant blood pressure drop during sedation. The American College of Cardiology and the American Heart Association advise caution with these medications on the morning of procedures involving anesthesia.
Diuretics (water pills) are also commonly held the morning of a colonoscopy. The bowel prep itself causes substantial fluid loss, and adding a diuretic on top of that can lead to dehydration and electrolyte imbalances that may trigger heart rhythm problems. Your doctor will tell you which specific blood pressure medications to take and which to skip that morning. Beta-blockers and calcium channel blockers are typically continued without changes.
Herbal Supplements
Several herbal products affect blood clotting and should be stopped before a colonoscopy. Garlic supplements have the strongest evidence linking them to surgical bleeding, even in people who aren’t on blood thinners. Hawthorn supplements carry a similar risk. Ginkgo biloba is a particular concern for anyone also taking warfarin: a large review of over 800,000 patient records found that combining ginkgo with warfarin significantly increased the risk of major bleeding events compared to warfarin alone.
Other supplements associated with bleeding risk when combined with anticoagulants include turmeric, chamomile, chondroitin-glucosamine, melatonin, fenugreek, milk thistle, and peppermint. Interestingly, fish oil, ginseng, and saw palmetto have been studied and show no meaningful association with bleeding. Still, many endoscopy centers ask patients to stop all herbal supplements 7 days before the procedure simply because the interactions for most products are poorly studied.
Fiber Supplements
Fiber supplements like psyllium (Metamucil), methylcellulose (Citrucel), and similar bulking agents should be stopped several days before your colonoscopy. A clinical trial found that starting psyllium-based fiber in the days before a colonoscopy actually worsened the quality of the bowel prep when a standard lavage solution was used. The fiber absorbs water and can create a thick residue that coats the colon wall, making it harder for the prep solution to do its job.
If you take fiber for hemorrhoids or regularity, stop it at least 3 to 5 days before the procedure. Your bowel prep solution will handle the job of clearing your colon, and any fiber residue left behind only works against that process.