Although some doctors scoff at the idea that free lunch can influence prescribing habits, a BMJ study published Thursday suggests that gift bans do have an impact on physician behavior. The study focused on students who attended medical schools with conflict-of-interest policies and strict gift bans as of 2004, comparing them to students who attended those same medical schools (and graduated) before the bans were implemented. The timing was somewhat serendipitous, appearing one day before the Centers for Medicare and Medicaid released its Sunshine rules regarding financial relationships between industry and medical professionals. It also comes just months after Massachusetts overturned its food ban and said it was OK for doctors to receive modest meals.

The study’s test case pertained to the prescribing habits for the stimulant lisdexamfetamine (Shire’s Vyvanse), the antipsychotic paliperidone (Johnson & Johnson’s Invega) and the anti-depressant desvenlafaxine (Pfizer’s Pristiq). Researchers chose to track these three drugs because they were among the top-selling drug classes at the time of the study and were new drugs within these classes. The study’s upshot: doctors who attended schools with gift restrictions “were significantly less likely than non-exposed physicians” to prescribe the newer medications over older medications within those same classes.

Researchers found that the gift-restricted doctors were less likely to prescribe the new-to-market stimulant lisdexamfetamine and the antipsychotic paliperidone than doctors who attended schools without gift restrictions, but both groups demonstrated similar prescribing rates when it came to the new anti-depressant, desvenlafaxine.

They also noted that although the number of medical schools with conflict-of-interest/gift guidelines is growing, many of the schools that were part of this analysis implemented the rules “because of state or military regulations, rather than as a result of internal school dynamics.”

Researchers said that before gift restrictions and bans, the American Medical School Association found that most medical students “received a gift or attended an industry sponsored event weekly.” AMSA launched its pro-ban PharmFree Campaign in 2002 in support of “evidence-based, rather than marketing-based prescribing” and compiles an annual Medical School scorecard that tracks policies and their robustness.

Researchers noted that they weren’t sure if the different prescribing behaviors could be completely attributed to the ban, as opposed to the ban and the educational component that discussed topics including conflict of interest. But the findings do suggest that despite protests from physicians who say they can remain impartial as long as everyone has the opportunity to buy them a cheeseburger, restricting soft interactions does affect physician behavior.

Also of note: although gift-ban discussions tend to focus on the industry-physician relationship, the Robert Wood Johnson Foundation’s January 2013 report on consumer attitudes shows that these conversations are being considered by patients, albeit from a different perspective. The foundation’s researchers found that although some patients said cost kept them from following doctors’ orders, it was not the only reason. Researchers said “several [respondents] mentioned that their physicians may have had a profit motive in recommending certain care,” and that was cited as another reason for not complying with a doctor’s recommendations.