Patients who take their medication exactly as prescribed following acute MI have a significant survival advantage. And that advantage is due to the effects of the drugs themselves—not just because patients are so-called “healthy adherers,” according to new research.

Though it’s long been known that adherence to evidence-based pharmacotherapy predicts better survival, this is the first attempt to find out whether the credit should go to the drug effects or the adoption of healthier lifestyles.

Between 1999 and 2003, researchers in Ontario, Canada, followed 31,455 MI survivors. All patients filled a prescription for statins, beta blockers, or calcium channel blockers. Both statins and beta blockers are recommended in secondary prevention of MI; calcium channel blockers are not.

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Patient adherence was then divided into three categories: high (meaning patients took their medication at least 80% of the time); intermediate (complied 40%-79% of the time); or low (complied <40% of the time). Investigators then compared the level of adherence with long-term mortality.

At a median of 2.4 years’ follow-up among patients who used statins, mortality was greatest for low adherers (24%); intermediate for average adherers (20%); and low for high adherers (16%). A similar but less pronounced dose-response-type adherence-mortality association was observed for beta blockers. There was no relationship between calcium channel blocker adherence and mortality (JAMA. 2007; 297:177-186).