See Spurling, Geoffrey K., Peter R. Mansfield, Brett D. Montgomery, Joel Lexchin, Jenny Doust, Noordin Othman, and Agnes I. Vitry. "Information from pharmaceutical companies and the quality, quantity, and cost of physicians' prescribing: a systematic review." PLoS medicine 7, no. 10 (2010): e1000352.
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. The narrative synthesis finding of variable results was supported by a meta-analysis of studies of prescribing frequency that found significant heterogeneity. The observational nature of most included studies is the main limitation of this review.
Regardless, their opinion is:
we recommend that practitioners follow the precautionary principle and thus avoid exposure to information from pharmaceutical companies unless evidence of net benefit emerges.
Dr. Steven Novella summarizes this study at his blog, Science Based Medicine.
five studies showed decreased prescribing quality, while five studies showed no association or ambiguous results. To me these are weak outcomes, without a clear answer.
After reading this review I am still left with the sense that the data on this important question is currently insufficient – it is mostly observational, and on the two most important questions (cost and quality) the evidence (while trending to the negative) is unclear. What is obvious is that better data would be helpful.
He also agrees that following the precautionary principle is prudent:
Meanwhile I think it is prudent to limit access of drug reps to physicians and their offices
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