What Vitamins Should You Stop Taking Before a Colonoscopy?

December 25, 2025 •

4 min read

According to the American Cancer Society, colonoscopies are a crucial screening tool that can help prevent colorectal cancer through the early detection and removal of polyps. For this procedure to be successful, a thorough and clean bowel is essential, which requires carefully managing your diet and certain supplements beforehand.

Quick Summary

A clear bowel is critical for an accurate colonoscopy. Certain vitamins and supplements, such as iron, vitamin E, and fish oil, must be discontinued prior to the procedure to prevent complications or an incomplete examination. Always consult your doctor for personalized instructions.

Key Points

Stop Iron Supplements: Discontinue iron supplements, including those in multivitamins, 7 days before your colonoscopy to prevent dark, tarry stools that obscure the colon lining.
Avoid Blood-Thinning Supplements: Stop taking blood-thinning vitamins and supplements, such as Vitamin E, fish oil, and certain herbs like Ginkgo Biloba, at least 5-7 days prior to reduce bleeding risk.
Discontinue Fiber Supplements: Stop all fiber supplements, including products like Metamucil, when you begin your low-residue diet to ensure the bowel prep is effective.
Review All Herbal Products: Consult your doctor about stopping any herbal supplements, as many can increase bleeding risk or interfere with other medications.
Consult Your Doctor: Always review your full medication and supplement list with your healthcare provider for personalized instructions, as every patient's needs are different.

Why Certain Supplements Must Be Avoided Before a Colonoscopy

Preparation for a colonoscopy is a vital step in ensuring the procedure is both safe and effective. A poorly prepared colon can obscure the doctor's view, leading to missed polyps, and in some cases, a need to repeat the entire procedure. Certain vitamins and supplements can directly interfere with this process in a few key ways:

Impact on Visibility: Some supplements can leave residue or cause discoloration in the colon, which can hinder the gastroenterologist's ability to see the bowel lining clearly. Iron supplements, for instance, can darken the stool, making it difficult to detect small abnormalities.
Increased Bleeding Risk: Vitamins and supplements that have blood-thinning properties can increase the risk of bleeding, especially if a polyp is removed during the procedure. This is a significant safety concern and is a primary reason for discontinuing specific products before the exam.
Interference with Bowel Prep: High-fiber supplements and some other products can thicken bowel contents, making the laxative preparation less effective and potentially leading to a suboptimal cleanse.

Specific Vitamins and Supplements to Stop Taking

Here is a list of common vitamins and supplements that most gastroenterologists recommend discontinuing before a colonoscopy. The timeline can vary, but generally, one week is the standard timeframe. Always follow your specific doctor's instructions.

Iron Supplements

Iron supplements, whether taken on their own or as part of a multivitamin, are a major concern. They cause the stool to become black and tarry, which can severely obscure the view of the colon wall and mimic the appearance of bleeding. For this reason, iron supplements must typically be stopped at least 7 days before the procedure.

Vitamin E

Known for its antioxidant properties, Vitamin E is also a natural anticoagulant, or blood thinner. Stopping Vitamin E, and other supplements with similar properties, is important to minimize the risk of bleeding that can occur during the removal of polyps. Most instructions advise stopping Vitamin E at least 7 days in advance.

Fish Oil and Omega-3 Fatty Acids

Like Vitamin E, fish oil and other omega-3 supplements are known for their blood-thinning effects. This can increase the risk of bleeding during the procedure, especially if a polypectomy is performed. It is standard practice to stop taking these supplements approximately one week before the colonoscopy.

Herbal Supplements

Many herbal supplements, while seemingly harmless, can have unpredictable effects and may increase the risk of bleeding. Common examples to avoid include:

Ginkgo Biloba
Garlic
Ginger
Turmeric
Ginseng
St. John's Wort

Fiber Supplements

While fiber is a key part of a healthy diet, fiber supplements like Metamucil, Benefiber, and Citrucel can slow digestion and leave behind residue in the colon, impeding the cleaning process. You should stop taking these in the days leading up to your procedure as directed by your doctor, usually at the start of your low-residue diet phase.

Multivitamins

The guidance on multivitamins can vary. Some sources advise stopping them completely, especially if they contain iron or Vitamin E. Other instructions may allow you to continue a multivitamin as long as it does not contain iron or other problem ingredients, and is stopped on the day of the procedure. The safest course of action is to check the ingredient list and consult your doctor for clarification.

Comparison of Supplements to Stop Before a Colonoscopy


Supplement Type	Primary Reason to Stop	Recommended Timeframe	Additional Notes
Iron Supplements	Can discolor stool, hindering visibility.	7 days	Always check multivitamins for iron content.
Vitamin E	Increases risk of bleeding.	5–7 days	A natural blood thinner, like many herbal supplements.
Fish Oil / Omega-3	Increases risk of bleeding.	7 days	The blood-thinning effect is the main concern.
Fiber Supplements	Obscures view with residue; reduces prep effectiveness.	Start of low-residue diet	Includes products like Metamucil and Citrucel.
Herbal Supplements	May increase bleeding risk or cause complications.	7–14 days	Includes Ginkgo, Garlic, Ginger, and Turmeric.

Always Consult Your Doctor

It is critical to remember that this is general information and should not replace your specific doctor's medical advice. Every patient's health profile and medication regimen is unique. You should always discuss your complete list of medications and supplements with your gastroenterologist well in advance of your procedure. They will provide detailed, personalized instructions to ensure your colonoscopy is as successful and safe as possible. Failing to follow these specific instructions can lead to a canceled or rescheduled procedure, wasting both your time and resources. You can read more about comprehensive preparation on the official website of the Colorectal Cancer Alliance.

Conclusion: Prioritize Safety for a Successful Exam

For an effective colonoscopy, proper bowel preparation is non-negotiable. This process includes carefully managing the intake of certain vitamins and supplements that can interfere with visibility or increase bleeding risks. Iron, Vitamin E, fish oil, and certain herbal and fiber supplements are among the most common products to temporarily discontinue. By communicating openly with your healthcare provider and following their precise guidelines, you can help ensure a clean and clear colon, leading to a successful procedure and accurate results. This vigilance and adherence to prep protocols are vital steps toward safeguarding your health.

Frequently Asked Questions

Most gastroenterologists recommend stopping all non-essential vitamins and supplements, including iron, fish oil, and Vitamin E, at least 5 to 7 days before your colonoscopy to minimize the risk of bleeding and ensure a clear examination.

It depends on the multivitamin's ingredients. If it contains iron, you must stop taking it one week before. If it does not contain iron or other blood-thinning components, some doctors allow you to continue until the day before. Always check with your doctor for specific guidance.

Iron supplements can cause your stool to turn a dark, tarry color, which can obscure the doctor's view of the colon wall and make it difficult to spot polyps or other abnormalities during the procedure.

In addition to vitamins, you should stop taking any herbal supplements (like Ginkgo, Garlic, and Turmeric) and fiber supplements (like Metamucil). Fish oil and other Omega-3 fatty acid supplements should also be avoided due to their blood-thinning properties.

You should stop taking fiber supplements at the same time you begin your low-residue diet, typically 3 to 5 days before your procedure, to prevent them from interfering with the bowel prep.

Forgetting to stop certain vitamins, especially blood thinners or iron, could lead to a less effective bowel prep, increased bleeding risk, or a compromised view for the doctor. In such cases, the procedure may need to be repeated, so it is crucial to follow instructions carefully.

For most supplements, you can resume taking them the day after your procedure, but you should confirm this with your doctor. If any polyps were removed, your doctor might provide specific instructions regarding when to restart certain medications or supplements.