People often don't appreciate being told they can't pick uptheir meds at the corner drug store. But more insurance plans arepushing enrollees onto so-called narrow pharmacy networks, in whichpeople are either incentivized or required to get theirprescriptions through certain pharmacies.

Narrow networks have long been criticized by smaller pharmacies,who are often left out of the networks, as well as consumers andadvocacy groups who say that such arrangements make it harder forpeople to get needed medication, particularly in rural parts of thecountry.

In contrast, big pharmacy chains, such as CVS, Walmart, RiteAidand Walgreens often benefit from the "preferred provider" statusfrom insurance plans.

Pushing back against criticism of the increasingly commonnetwork system, CVS recently released a study stating that peopletake their medication more regularly after switching from anon-network plan to a narrow network.

CVS conducted the study by reviewing claims data for 200,000patients with prescriptions for high blood pressure, diabetes, highcholesterol and depression over a 12 month period.

For all four types of medication, those enrolled in non-networkplans reported a medication possession ratio (MPR) between 1.59percent and 2.85 percent higher than those enrolled in narrownetworks.

However, the study also showed that MPR increased more for thoseenrolled in a plan that implemented a narrow network than for thosewho remained in a non-network plan. Plans that implemented narrownetworks saw the rate increase between 1.37 percent and 1.77percent for all four classes of medication. During the same time,the MPR of those in non-network plans remained higher, butrelatively flat, only increasing between 0.12 percent and 0.6percent.

CVS is touting the study as evidence that narrow networks canimprove medication practices by establishing a "pharmacy home" forbeneficiaries.

"Despite common concerns that narrow pharmacy networks reduceaccess, we believe they can actually help encourage plan members toestablish a pharmacy home where patients with chronic diseases canreceive coordinated care and effective medication adherencesupport," said William Shrank, MD, the study's author.