In the aftermath of the agreement between Walgreens and Express Scripts wherein the nation’s largest drug chain will once again honor prescriptions from Express Scripts members, a competitive battle has emerged between Walgreens and CVS, its No. 1 rival.

Simply put, CVS is anxious to retain the new patients it gained over the eight-month period during which Walgreens was precluded from serving Express Scripts patients. For its part, Walgreens wants them back.

Each has much at stake. During that interval when Walgreens lost the business of many Express Scripts members, CVS gained much of that business, with the result that the company saw overall sales increase by 8.4% to $31.87 billion during the first half of 2012.

For its part, Walgreens reported a 3% sales decline for the same six months to $35.04 billion, a dip that removed some of the gloss from its positive achievements during the period, most notably its merger with Alliance Boots.

So the battle has been drawn. CVS has been running ads giving the reasons “millions of Express Scripts members have chosen CVS/pharmacy.” Among them:

• CVS pharmacy has always accepted Express Scripts plans.
• Personalized expert advice.
• ExtraSavings and ExtraBucks Rewards from ExtraCare.
• Many 24-hour and drive-through locations.
• Flu shots every day, every store — insurance accepted.

Meanwhile, Walgreens is working equally diligently to get those customers back. To that end, a recent ad included this message: Welcome Express Scripts members. To find out if you can switch back to Walgreens, just talk to us or visit Express-Scripts.com.

As an added inducement, the ad offered a $25 Walgreens card for those Express Scripts customers who returned to Walgreens for prescriptions.

No two observers agree as to where this competition will ultimately lead, but the prevailing opinion is that Walgreens will win back some, but by no means all, of its Express Scripts customers.

However, bigger issues are already emerging that may well diminish the importance of this latest CVS-Walgreens skirmish. Foremost among them, of course, is the path on which Walgreens has embarked to merge with Alliance Boots, the most powerful drug retail/wholesale entity outside the United States. That alliance, going forward, will almost certainly alter the dynamics of the PBM equation — and may well diminish the importance of PBMs in the future.

Then too there’s the upcoming election — and the future of President Obama’s Affordable Care Act. Should Obama win, and the health care act proceed unimpeded, the pharmacy component will certainly change within the next two years. So, too, might the role of the pharmacy benefit manager.

But perhaps the biggest lesson learned by the parties involved in the Walgreens-Express Scripts battle is this one: Consumers may be loyal to a particular drug store or drug chain — but only to a point. Once that loyalty begins costing them money — or once they begin to believe that that loyalty is costing them money — they will gladly switch to the drug store where they believe the value is more appealing. The people at Walgreens were likely disappointed on confronting this reality. The people at CVS will likely be confronted with it in the future.

This is sad in a way. Indeed, it probably says more about today’s chain drug store than it does about the consumers who shop there. It says that, in the main, the similarities among today’s chain drug stores outweigh the differences.

More disappointing still, chain drug stores probably have more in common with each other than, say, supermarkets or discount stores. Who, after all, would confuse a Walmart Supercenter with an H-E-B, or a Walmart with a Target? But surely many shoppers see little difference between a Walgreens drug store and one operated by CVS.

That’s probably why the inducements CVS uses in its ad to retain Express Scripts members could just as easily, and effectively, be cited by Walgreens in an effort to bring them back.