Joseph Mercola, D.O., runs the website which is full of misinformation, advocates all kinds of questionable alternative treatments including homeopathy, and discourages vaccination and other aspects of conventional medicine.

Like Dr. Oz and Andrew Weil, he is more dangerous than easily recognizable quacks in that he combines some good medical information with egregious misinformation, and readers who know he is right about the good information are likely to wrongly assume everything else he says must be equally true. He’s right about some things, but the safest course is to assume that anything on his website is false unless you can verify it as true by consulting other sources that are reliable. I tried to verify the information in his recent article on colonoscopy. I found outright errors along with fear-mongering and bias.

What Mercola says about colonoscopy

The webpage is headed by a video that tells us:

  • There are 3 options for colon cancer screening: colonoscopy, sigmoidoscopy, and annual fecal testing for occult blood (FOBT). Doctors decide patients should have colonoscopy rather than informing them of the other options and giving them a choice. [Patients deserve to have enough information to give informed consent, and it is true that doctors seldom take the time to discuss all the pros and cons with patients, but many patients are content to trust the doctor’s judgment and don’t want to hear all the confusing details. And none of that is an argument against colonoscopy itself – HH]
  • Colonoscopies are not used as much in other countries. [Of course they aren’t. In other countries they are not as readily available and the high cost is a consideration. That doesn’t mean doctors in other countries think colonoscopy isn’t advisable – HH]
  • Colonoscopies are profitable; doctors get paid by the procedure. [That doesn’t mean they aren’t the best choice. And colonoscopies are recommended just as often in DOD health facilities and other systems where doctors are not paid more for doing more procedures – HH]
  • They are expensive because the AMA sets the prices. [False! The AMA doesn’t set prices for anything, and the price varies widely according to geographic location and other factors – HH]
  • PCPs recommend them because they get financial kickbacks. [No, PCPs recommend them because they know the evidence supports them – HH]

The video is by Dr. Michael Greger. I don’t consider him a reliable source. I wrote about another of his videos here.

Both Greger and Mercola make these claims:

  • “1 in 350 colonoscopies end up doing serious harm.”
  • “The death rate is about 1 for every 1000 procedures.”

I questioned those numbers and looked for reliable sources.

What the evidence says

I found a position statement of the American Society for Gastrointestinal Endoscopy that includes a thorough discussion of all the complications of colonoscopy. Based on a review of published data, they estimate the colonoscopy-specific mortality as 0.007%. They provide citations.

I found the supporting documents that the USPSTF used to develop its recommendations. Figure 1 shows the proportion of serious complications as 0.00277.

Faulty reasoning

Under “risks of colonoscopy” and “false positives” Mercola mentions that 30-40% of men treated for prostate cancer were treated unnecessarily. That is a risk of indiscriminate screening for prostate cancer; it has nothing whatsoever to do with colonoscopy. He doesn’t tell us what the false positive rate is for colonoscopy. As a matter of fact, colonoscopy is the gold standard for finding out if the results of other colon cancer screening tests are false positives (or negatives). If you have a positive fecal occult blood test, the next step is colonoscopy. And of course no discussion of risks is meaningful without putting those risks into perspective with the lives saved and other benefits. He fails to do that.

He spends a lot of time discussing the proper sterilization of colonoscopes. He claims that colonoscopes and sigmoidoscopes are impossible to clean! That’s demonstrably untrue. It goes without saying that the instruments should be properly cleaned between patients. The reported incidence of infection with endoscopy is very low, around 1 in 1.8 million procedures, and the CDC has published guidelines for disinfecting endoscopes that should prevent even those cases.

He recommends using peppermint oil. Indeed, PubMed lists a couple of studies showing benefits from peppermint oil instilled into the colon. There is a single double-blind study showing that taking it orally facilitates colonoscopy by reducing spasm; it was a small study with only 33 patients in the peppermint oil group. It sounds promising, and might be worth trying, but the study will have to be replicated and confirmed before peppermint oil can be recommended as a standard part of the colonoscopy prep. So he’s not “wrong” about peppermint oil, but the impression he gives of its benefits goes beyond the actual evidence.

Near the bottom of the page, Mercola asks “Should you have routine colonoscopies starting at age 50? To his credit, he admits that visual inspection is the most reliable way to check for colon cancer, and that colonoscopy can remove precancerous polyps and could save your life. But he prefaces these facts with this inanity:

I’m 61 and I’ve never had a colonoscopy and have no plans of ever getting one. While I believe they can be valuable as a diagnostic tool, I feel confident that with my diet (which includes daily amounts of raw turmeric) and lifestyle it’s highly unlikely I would develop colon cancer.

That’s wishful thinking, not science. There is some preliminary evidence that certain dietary interventions may be effective in modestly reducing the risk of some cancers, but they don’t eliminate the risk. The Natural Medicines Comprehensive Database states there is insufficient reliable information to rate the effectiveness of turmeric in colorectal cancer prevention (and I’ve discussed the lack of good evidence for turmeric as medicine before). It is foolish to refuse colonoscopy based on such scanty evidence.

Mercola influences a lot of people, and the overall impact of this article is negative. It will likely persuade a lot of his readers to forgo a potentially life-saving procedure. You can see from the comments on his website that many of his readers reject not only colonoscopies but mammograms, public health measures like vaccination and fluoridation, and sometimes even conventional medicine as a whole.

Mercola is untrustworthy

His website is featured on Skeptoid’s recently updated list of the top 10 worst anti-science websites:

Moving up from #6 on our previous list to #3 this time is the sales portal of anti-vaccine activist Joseph Mercola. Since our last episode, he’s received at least one more warning letter from the FDA (to add to his ever-growing collection) for failing to test whether some of his supplement products actually contain the advertised ingredients. To drive his estimated $7 million in annual sales, Mercola parrots a staggering array of long-debunked unscientific claims: that genetically modified crops are harmful, that microwaving food makes it poisonous, that cell phones cause cancer, that AIDS is caused not by HIV but by a diet lacking in his products, that organic food is a superior substitute for medical care, and that using sunscreens other than the all-natural version he sells is the true cause of skin cancer.

Among Skeptoid’s 10 anti-science websites, 5 are medical websites. NaturalNews is ranked as number 1, and Dr. Oz, the FoodBabe, and Deepak Chopra follow Mercola at 5, 7, and 8 respectively.

Mercola features on other lists of untrustworthy websites including FatFighterTV and Quackwatch.

Mercola is notorious on the Science-Based Medicine website. A 2009 article by Joseph Albietz listed 9 reasons to completely ignore Mercola. David Gorski wrote about him here, here, and here. And Steven Novella has written about him on the Neurologica blog.

Mercola is also featured in The Skeptic’s Dictionary and his Wikipedia article has links to numerous other sources criticizing him.

As if we didn’t already have enough evidence that Mercola is untrustworthy, it has just been revealed that his Organic Daily Face Cleanser (with his name emblazoned on it) contains pesticides and a carcinogen!

Conclusion: Mercola’s discussion of colonoscopy is incomplete and misleading

I reviewed the evidence for colonoscopy here. Briefly, colon cancer screening is clearly beneficial for those over 50, and there are pros and cons to each of the three recommended screening methods. The FOBT has more false positives and negatives and the false positives require further evaluation with colonoscopy, sigmoidoscopy only examines part of the colon, and colonoscopy allows for gold-standard visualization of the entire colon and biopsy of suspicious lesions but it involves more risks, inconvenience, and cost than the other options. I will repeat what I said before: “if you are approaching the age of 50, you have a decision to make: not whether to be screened, but which screening test to choose.”

Mercola’s discussion of colonoscopy is incomplete and misleading. It is one more example among many that he is not a reliable source of science-based medical information. Visiting his website could be hazardous to your health.


Posted by Harriet Hall

Harriet Hall, MD also known as The SkepDoc, is a retired family physician who writes about pseudoscience and questionable medical practices. She received her BA and MD from the University of Washington, did her internship in the Air Force (the second female ever to do so),  and was the first female graduate of the Air Force family practice residency at Eglin Air Force Base. During a long career as an Air Force physician, she held various positions from flight surgeon to DBMS (Director of Base Medical Services) and did everything from delivering babies to taking the controls of a B-52. She retired with the rank of Colonel.  In 2008 she published her memoirs, Women Aren't Supposed to Fly.