Several categories of medications need to be stopped or adjusted before a colonoscopy, and the timing varies from seven days to just one day before the procedure depending on the drug. The most common ones to pause include blood thinners, certain pain relievers, diabetes medications, iron supplements, and some herbal supplements. Your gastroenterologist’s office will typically provide a personalized list, but here’s what to expect and why each category matters.
Blood Thinners and Antiplatelet Drugs
Blood-thinning medications are the most carefully managed drugs before a colonoscopy because they increase bleeding risk, especially if the doctor needs to remove polyps during the procedure. The timing for stopping each one differs based on how long it stays active in your body.
Warfarin (Coumadin) should be stopped five days before the procedure. It takes that long for your body to restore normal clotting ability after discontinuation. Newer blood thinners like apixaban (Eliquis), rivaroxaban (Xarelto), edoxaban (Savaysa), and betrixaban only need to be held for one to two days beforehand because they clear your system faster.
Clopidogrel (Plavix) and prasugrel, which prevent platelets from clumping together, require a longer pause of seven days before the colonoscopy. These drugs permanently alter platelets, so your body needs time to produce fresh ones.
Here’s an important nuance: the American Society for Gastrointestinal Endoscopy notes that a routine diagnostic colonoscopy with basic biopsies is considered a low-risk procedure for bleeding. If no polyps are expected to be removed, your doctor may actually tell you to continue your blood thinner. The stoppage guidelines above apply when there’s a reasonable chance polyps will need to be removed, which bumps the procedure into the higher-risk category. This is why your prescribing doctor and your gastroenterologist both need to weigh in on the decision.
NSAIDs and Pain Relievers
Non-steroidal anti-inflammatory drugs like ibuprofen (Advil, Motrin), naproxen (Aleve), meloxicam, and indomethacin should be stopped one week before your colonoscopy. These medications interfere with platelet function and can increase bleeding if polyps are removed.
Aspirin is handled differently. Low-dose aspirin (81 mg) is generally safe to continue through the procedure, even for higher-risk endoscopic work. If you take aspirin for heart protection, you’ll likely be told to keep taking it. Acetaminophen (Tylenol) is also fine to use for pain relief during the days you’re off NSAIDs, since it doesn’t affect clotting.
Diabetes Medications
Diabetes drugs require careful adjustment rather than a simple stop, because the fasting and clear-liquid diet involved in colonoscopy prep can cause dangerously low blood sugar. The changes typically start the day before the procedure when you switch to clear liquids.
Metformin should be stopped once you begin the clear liquid diet, which is usually the day before your colonoscopy. You can resume it once you’re eating regular meals again after the procedure. The concern with metformin during fasting is a rare but serious buildup of lactic acid.
Insulin adjustments depend on the type you take:
- Rapid or short-acting insulin: Cut your dose to 50% once you start the clear liquid diet. If you normally dose based on carb counting, continue using your usual ratio for whatever you consume.
- Intermediate-acting and first-generation basal insulins (like NPH, Lantus, or Levemir): Take 80% of your normal dose the full day before the procedure, then 50% the morning of.
- Second-generation basal insulins (like Tresiba or Toujeo): People with type 1 diabetes should take 50 to 80% of their normal dose starting the day before, while people with type 2 diabetes should take 50%.
The goal is to prevent both dangerously low blood sugar from too much insulin without food and dangerously high blood sugar from skipping insulin entirely. Monitor your glucose more frequently during the prep period.
Iron Supplements and Fiber
Iron supplements should be stopped at least seven days before your colonoscopy. Iron turns your stool dark and creates a thick residue that coats the lining of the colon, making it difficult for the doctor to see the tissue clearly. Even small amounts of residue can obscure polyps or other abnormalities.
Fiber supplements need to be stopped at least five days before the procedure for similar reasons. Fiber creates bulky residue that’s harder for the bowel prep solution to flush out completely. If your colon isn’t clean enough when you arrive, the procedure may need to be rescheduled, which means going through the entire prep process again.
Most facilities will also ask you to shift to a low-residue diet starting about three days before the colonoscopy. This means limiting high-fiber foods like raw vegetables, whole grains, nuts, and seeds.
Herbal Supplements
Several popular herbal supplements interfere with blood clotting and should be stopped at least one to two weeks before a colonoscopy. The two most concerning are ginkgo biloba and garlic supplements.
Ginkgo contains compounds called ginkgolides that block platelet aggregation through a different pathway than prescription blood thinners. Studies have documented spontaneous bleeding in people taking ginkgo, and the risk is compounded when combined with aspirin or other NSAIDs. Garlic supplements similarly inhibit platelet clumping and have been linked to excessive surgical bleeding. One case involved prolonged hemorrhage after a routine procedure in a patient who had been taking garlic tablets. Both supplements also amplify the blood-thinning effects of prescription anticoagulants like warfarin.
As a general rule, disclose all supplements to your gastroenterologist’s office during your pre-procedure call. Fish oil, vitamin E in high doses, turmeric, and ginger supplements can also have mild blood-thinning properties.
Anti-Diarrheal Medications
Medications that slow down your gut, such as loperamide (Imodium) and bismuth subsalicylate (Kaopectate, Pepto-Bismol), should be stopped seven days before the procedure. These drugs work against the bowel prep by slowing intestinal movement and leaving residue behind. Bismuth-containing products also darken stool, which can obscure the doctor’s view.
Medications You Can Usually Keep Taking
Most blood pressure and heart medications are continued right up to and including the morning of your colonoscopy, taken with a small sip of water. This includes beta-blockers, ACE inhibitors, and calcium channel blockers. Stopping blood pressure medications abruptly can cause dangerous rebound spikes in blood pressure, so doctors almost always want you to keep taking them.
Thyroid medications, anti-seizure drugs, and most antidepressants are also typically continued on their normal schedule. The key exception is any medication that’s a capsule or tablet you can’t take with just a small sip of water within the fasting window your facility specifies, usually two to four hours before your arrival time.
Because colonoscopy prep involves fasting and significant fluid loss, the combination of medications you take matters. If you’re on several of the drug categories mentioned above, your doctor’s office should walk through each one individually. Bring a complete medication list, including over-the-counter drugs and supplements, to your pre-procedure appointment or phone consultation so nothing gets missed.