Anti-depressants may not be as effective as patients -- and doctors -- believe.

NEW YORK (CNNMoney.com) -- Patients and doctors alike may have received some fuzzy truth about the effectiveness of antidepressant medication.

According to a report in The Wall Street Journal, many studies have found that best-selling antidepressants like Wyeth's Effexor and Pfizer's Zoloft may have little or even no effect on patients. Many of those studies, though submitted to the Food and Drug Administration, were left unpublished.

Researchers accordingly suggested in this week's New England Journal of Medicine that doctors and patients may not have been able to see the full antidepressant picture.

Both Pfizer (PFE, Fortune 500) and Wyeth (WYE, Fortune 500) told The Wall Street Journal that they will disclose all study results, but they will not necessarily publish them in medical journals. The FDA does not require pharmaceutical companies to publish the studies that they sponsor, which leaves many studies unpublished.

Separately, 74 studies involving 12 antidepressant drugs were submitted to the FDA between 1987 and 2004, 38 of which the FDA called "positive." Though all but one of the "positive" studies were published, only 14 of the 36 "negative" studies were printed in medical journals.

But even with the large disparity of reports that the pharmaceutical companies published, not all of the negative stories were all that "negative."

According to the NEJM researchers, at least 11 of the 14 "negative" studies presented unfavorable findings as beneficial ones by highlighting positive secondary outcomes and ignoring negative primary results.

The New England Journal of Medicine researchers believe this "publication bias" can complicate doctors' understanding of the effectiveness of medications. For instance, when considering all of the studies' data, the researchers found that Zoloft only has a "small" effect on patients as opposed to the "medium" effect that the mostly-positive results had shown.