I have been waiting for some time to post this information and am delighted finally to be able to do it--see the article just published on line in PLoS Medicine:
This article by Spurling et al. represents the brain trust of Healthy Skepticism in Australia, with input from Canada's Joel Lexchin--in short, the people around the world who have most closely tracked the evidence for drug industry influence over medical practice.
The problem they set out to address is one I explained some time back:
The ideal evidence that we pharmascolds seek--that accepting gifts and information from the drug industry leads to worse prescribing by docs--will never be available because the necessary randomized, controlled trial that would establish causation will never be done. Pharmapologists have seized upon this situation to assert the opposite state of affairs, that there's simply no evidence at all of harm arising from industry marketing, therefore we pharmascolds base our position solely on ideology and not on evidence. As I have also noted, we pharmascolds make things worse by repeatedly, in knee-jerk fashion, citing the systematic review by Wazana in JAMA, 2000. This review is now nearly worthless for two reasons. First, it's woefully out of date; second, if you read it carefully, it "proves" almost nothing--perhaps that more contact with drug reps makes docs who serve on formulary committees more likely to recommended company drugs.
In short, what we have needed for a long time is an up-to-date, very careful review of the existing literature that addresses the actual evidence base for the argument against drug company influence. Finally we have that review.
Spurling et al. surveyed the literature and carefully pared down their sample to 58 published studies. Almost all of these were observational studies. They were able to do a meta-analysis of one set of studies, but mostly had to do a narrative review because of the heterogeneity of the research methods. In short they were quite careful not to claim more than they could back up.
I will copy their abstract as to their main findings:
"Of the set of studies examining prescribing quality outcomes, five found associations between exposure to pharmaceutical company information and lower quality prescribing, four did not detect an association, and one found associations with lower and higher quality prescribing. 38 included studies found associations between exposure and higher frequency of prescribing and 13 did not detect an association. Five included studies found evidence for association with higher costs, four found no association, and one found an association with lower costs. "
"With rare exceptions, studies of exposure to information provided directly by pharmaceutical companies have found associations with higher prescribing frequency, higher costs, or lower prescribing quality or have not found significant associations. We did not find evidence of net improvements in prescribing, but the available literature does not exclude the possibility that prescribing may sometimes be improved. Still, we recommend that practitioners follow the precautionary principle and thus avoid exposure to information from pharmaceutical companies."
My own way of stating the results: There are a lot of reasonably well-done studies of the subject, given the inherent limitation that only observational studies and not randomized trials are usually feasible. These studies show that when an influence can be detected, drug industry marketing exerts a negative influence on the quality of physicians' prescribing (including unnecessarily higher costs as a negative feature). It is vanishingly rare to find a study that shows an improvement in quality. There is a body of evidence, and it overwhelmingly tilts in the direction of supporting recommendations that physicians try to minimize influence from and contact with the industry.
Wazana A (2000) Physicians and the pharmaceutical industry: is a gift ever just a gift? JAMA 283: 373–380.