Ever wonder why you're on that specific antidepressant, or taking a certain birth control pill? It could have been a gift or nice meal courtesy of a pharmaceutical sales rep that nudged your doctor to prescribe it. Restrictions on those kinds of incentives can result in physicians suggesting lower-cost generic drugs instead, according to a just-released study in the Journal of the American Medical Association.

The process by which pharma reps visit doctor's offices has a nice-sounding name: detailing. During their visits to educate MDs on their company's drugs, they might treat the doctor and their staff to a meal or offer other gifts. These incentives—however small—can have a big impact.

To investigate the effects of detailing, researchers looked at more than 16 million prescriptions written between January 2006 and June 2012 for 262 drugs within eight major drug classes, including statins, antidepressants, gastroesophageal reflux drugs, sleep aids, and ADHD drugs. The authors got data on the size of the national sales forces and market share for specific drugs from a market research firm.

They aimed to compare how doctors at 19 academic medical centers in five states (California, Illinois, Massachusetts, Pennsylvania, and New York) changed the way they wrote prescriptions before and after their employers put limits on detailing. The authors then compared these doctors to an even bigger group of similar MDs who didn't have to abide by such policies; they served as the control.

Some of these restrictions included banning personal gifts and some meals and regulating access to hospitals. (For instance, salespeople couldn't go into patient care areas.) Doctors subject to detailing policies were still allowed to meet with pharma reps.

Before these restrictions were put in place, drugs that were "detailed" held a 19.3 percent market share on average. But after these policies were enacted, that market share fell by 8.7 percent (or 1.67 percentage points) in six of the eight drug categories, and prescribing of non-detailed drugs increased by 0.84 percentage points from a previous market share of 14.2 percent. Doctors also started prescribing more generics. That's a big deal: Generic drugs are 80 to 85 percent less expensive than brand-name ones. Changes in prescribing were evident whether or not a generic version of a detailed drug became available during the study period. This study is the largest, most comprehensive analysis of detailing restrictions to date.

"Physicians make dozens of decisions around prescribing every day…The decision whether to prescribe Drug A or Drug B in a certain drug class is often not among the most critical of decisions the physician will make, because the two drugs are similar in their efficacy, and the patient's copay might vary by only a few dollars," says study co-author Ian Larkin, assistant professor of strategy at the UCLA Anderson School of Management.

What's going on? Is the lure of a free lunch really that powerful? Actually, it can be, the authors say. And it's not necessarily because your doctor is purposely trying to give you more expensive meds; it's often a silent influence that the doctor might not recognize.

"Psychological mechanisms such as reciprocity—whereby the receiver of a gift feels an unspoken, often unperceived need to repay the gift-giver—have been demonstrated to affect decisionmaking in situations such as these," Larkin explains. He added in a release that "the fact that regulating gifts while still allowing sales calls still led to a switch to cheaper, generic drugs may suggest that gifts such as meals play an important role in influencing physicians."

He's quick to point out that their observational study doesn't prove that this is what's happening with prescriptions—there could have been other factors at work—but it's the most likely mechanism based on prior research on how gifts influence decisions.

And the standard practice for a physician to disclose potential conflicts of interest with a patient doesn't do much to fix the problem, either. In fact, patients often have no clue what it means anyway, he says.

"A large body of research also shows that simply disclosing conflicts of interests is insufficient to reduce their influence, and may even exacerbate it. The results from this study underline the effectiveness of, and need for, centralized rules and regulations," George Loewenstein, a professor of economics and psychology at Carnegie Mellon University and the co-author of the study, said in a press release. "We should not put the onus of dealing with conflicts on patients; the best policies are those that eliminate conflicts."

Not only do medical centers need to enact detailing policies, but removing incentives and conflicts of interest can go one step further by moving doctors to a salary-based model, Larkin and Loewenstein write in an editorial, also published in JAMA this month, a theme issue on conflict of interest.

They argue that physicians in a fee-for-service model who get payments from third-party companies for tests and procedures are more likely to order them for their patients. This can drive up the cost of medical expenses, not to mention that unnecessary testing can lead to anxiety, unneeded follow-up care, and wasted money.

And, yes, a salary model is realistic. In fact, some health systems already do it, including the Mayo Clinic, Cleveland Clinic, and the Kaiser group, they write. "Furthermore, many decades ago, it was the most common way physicians were compensated. Fee-for-service compensation has exploded in recent decades, but not a lot of thought has been put into the direct financial incentives this gives physicians, which often go against the needs of patients," Larkin says.