Journal of Medical Ethics: 2006 32:559-563
“Most respondents (doctors) thought it proper to accept drug samples (92%)… A third (33%) of the respondents thought that their own decision to prescribe a drug would probably be influenced by accepting drug samples… Respondents who distributed drug samples to patients indicated doing so because of patients’ financial need (94%) and for their convenience (76%) and less so as a result of knowledge of the efficacy of the sample product (63%)…
http://jme.bmj.com/cgi/content/abstract/32/10/559

also found at:
http://www.ncbi.nlm.nih.gov/pubmed/17012493;
http://cat.inist.fr/?aModele=afficheN&cpsidt=18138555