Eighty percent of Internet users seek out health information on the web, according to a survey released by the Pew Internet & American Life Project at the beginning of February. It’s the third most common online activity after sending e-mail and using a search engine.

So which among the myriad health information sites are the most trustworthy? It can be hard to tell, especially since there is almost a complete lack of third-party evaluations online—or in any of the news media—at a time when they would seem to be more useful than ever.

That is why it was so refreshing to see The New York Times Magazine’s Virginia Heffernan cause a stir with a February 4 column headlined “A Prescription for Fear.” In it, she blasted one of the Web’s most popular for-profit health information sites, WebMD, arguing that it is “permeated with pseudomedicine and subtle misinformation.” Calling it “synonymous with Big Pharma Shilling,” she urged readers to block the site “because of the way WebMD frames health information commercially, using the meretricious voice of a pharmaceutical rep…”

By way of comparison, Heffernan plugged MayoClinic.com, run by the world-renowned nonprofit research hospital in Rochester, Minnesota. There, she promised, readers would find: “No hysteria. No drug peddling. Good medicine. Good ideas.”

In order to illustrate her point about commercial framing, Heffernan searched Google for “headache” and “Mayo Clinic,” and “headache” and “WebMD.” The latter leads to WebMD’s “Migraines and Headaches Health Center,” which features a bunch of scary looking photos of people in significant pain and prominently recommends medication. The former search leads to Mayo’s much more sedate page for a “Tension Headache,” which is photo-less and recommends non-drug treatments before pain relievers. It’s a strong example of the differences between the two sites—but many people quickly pushed back in social media and on blogs.

Adam Grossberg, the senior vice president of corporate communications at WebMD, quickly responded via Twitter. In a string of tweets, Grossberg told his followers, “Opinion or not - would have expected a call,” and that the Times should have disclosed “its ownership of an ad-supported site that competes with WebMD,” referring to About.com Health. He also wrote, “WebMD’s content undergoes a rigorous medical review to ensure it’s credible and accurate, and we clearly distinguish editorial from ads.”

At the blog eHealth, John W. Sharp applied Heffernan’s search method for “headache” to “fibromyalgia.” He found that the resulting pages at Mayo and WebMD both display a Pfizer ad touting “a treatment option” for fibromyalgia, but the former also has ads from Google while the latter does not. (Sharp pointed out that Mayo and WebMD each have policies laying out fairly strict guidelines for accepting ads, and state that ads should not be considered endorsements of their products and/or services. He also noted that Mayo and WebMD are both HON Code certified and that WebMD also has eTrust and URAC shields. These are fairly well known and accepted standards, but a 2009 paper in the journal Informatics for health & Social Care argued that the “validity and reliability of these quality tools and their applicability to different health websites varies.”)

In the actual text of the “fibromyalgia” pages, however, Mayo recommends “lifestyle and home remedies,” “alternative medicine,” and “copying and support,” whereas WebMD cuts straight to a list of medications. This led Sharp to conclude, “there may be something WebMD suggesting drug treatment more often than Mayo Clinic, but [Heffernan’s] article fails to mention that MayoClinic.com is supported by advertising and in some cases has more ad per page than WebMD.” (Actually, Heffernan does mention that Mayo takes drug ads, but only says so in a discreet sidebar.)

An informal poll of six health reporters revealed they’d all recommend the Mayo Clinic site over WebMD, partly because of the commercial veneer at WebMD, but mostly because of the world-class research center behind Mayo’s site (reflecting reporters’ general preference for primary sources of information). None said they’d go as far as Heffernan in terms of advising people to block WebMD, however. Moreover, they would all recommend a number of sites other than or in addition to Mayo, depending on a person’s particular needs. Indeed, in terms of the wide variety of sources of medical information available online, Heffernan’s article was very limited in scope, and the point of this review is not to settle the debate she started, but rather to expand upon it.

Curtis Brainard writes on science and environment reporting. Follow him on Twitter @cbrainard.