Wikipedia:MEDRS

Ideal sources for biomedical information include: review articles (especially systematic reviews) published in reputable medical journals; academic and professional books written by experts in the relevant fields and from respected publishers; and guidelines or position statements from national or international expert bodies. Primary sources should generally not be used for medical content – as such sources often include unreliable or preliminary information, for example early in vitro results which don't hold in later clinical trials.

In the biomedical literature:

There are also sources discussing content about health in the general news media. These generally should not be used to source content about health but may be useful for "society and culture" content. Please see Popular press below.

Findings are often touted in the popular press as soon as original, primary research is reported, before the scientific community has analyzed and commented on the results. Therefore, such sources should generally be entirely omitted (see recentism). Determining weight of studies generally requires reliable secondary sources (not press releases or newspaper articles based on such sources). If conclusions are worth mentioning (such as large RCTs with surprising results), they should be described appropriately as from a single study:

"A large, NIH-funded study published in 2010 found that selenium and Vitamin E supplements increased risk of prostate cancer; they were previously thought to prevent prostate cancer." (citing PMID 20924966)

Given time a review will be published, and the primary sources should preferably be exchanged for the review. Using secondary sources then allows facts to be stated with greater reliability:

"Supplemental Vitamin E and selenium increase the risk of prostate cancer." (citing PMID 23552052)

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