In general, failure to do so is a violation of federal law, and by extension, state law, according to Catizone. That's a problem, because warfarin is among the most likely prescription drugs to cause serious adverse reactions leading to emergency-room visits, and requires clear guidance. Representatives of Target and CVS told us that their pharmacies automatically print medication guides for patients. But those guides did not make it to our staff members' packages. At press time, Walgreens and Walmart had not responded to our queries. All of the pharmacies did provide their own patient materials, known as consumer medication information (CMI) - and all the materials included the most important "black box" safety warnings about the risk of bleeding. But, they differed from the FDA-approved guide, and proved confusing even for our health reporters to decipher.