Misunderstandings between doctors and patients about how and when to take medicines are surprisingly common. In one study, for instance, nearly half of the patients who needed an anticoagulant drug to prevent formation of blood clots weren’t taking their medication as instructed—and didn’t realize they were doing anything wrong. If such confusion is widespread, this could spell big trouble since more than 2 million Americans now need anticoagulants to help prevent strokes.

Chances are that misunderstandings about drug issues are more common when doctor and patient don’t speak the same language or when a patient has memory issues. On the other hand, researchers from the University of California at San Francisco (UCSF) think everyone who is handed a prescription could benefit from a system they’ve devised.

First, doctors ask patients to describe how much medication they take and how often they take it. Next, patients are given a new computer-generated tool called a Visual Medication Schedule (VMS). This color-coded weekly calendar has instructions in English and, if necessary, in a patient’s native language. Finally, patients summarize what they understand about using their medications before leaving their doctor’s office.

In tests, VMS worked well for at-risk stroke patients whose lab results showed their medication wasn’t keeping their blood thin enough to prevent clots. Those using the VMS system got their blood to a “safe” level almost twice as fast as patients who received only verbal and written instructions.

Although VMS systems are still in production, it’s always a good idea to review your medications at every doctor’s visit, according to UCSF researcher Edward Machtinger, MD. “Far too often, patients get additional medication, say for blood pressure, because their symptoms call for it—without first checking if the existing drug is being used properly,” he says.

Keep this in mind: If your medicine doesn’t seem to be working, check with your doctor to make sure you’re taking it correctly. That chat could save your life.