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	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

In the article by Krumholz et al¹ on the interaction of aspirin and angiotensin-converting enzyme (ACE) inhibitors, the authors concluded that when prescribed together, the mortality rate after a myocardial infarction is slightly lower than it is when either drug is prescribed alone, although the added benefit is not statistically significant. They based their conclusion on the P value of a product term between both drugs entered in a Cox regression model. Hence, they use a purely statistical definition of interaction rather than a biological approach. Conclusions based on this approach of interaction are often misleading, if not incorrect, because the magnitude or statistical nonsignificance of a product term is by no means a proof of the absence of interaction.² We believe that this interaction should be understood as the joint effect of 2 drugs in the same causal (or preventive) mechanism of a disease.³

We used the data provided . . . [Full Text of this Article]