NSAIDs interact with the endocannabinoid system and its endocannabinoids, as COX2 have been shown to utilize endocannabinoids as substrates, and may have a key role in both the therapeutic and adverse effects of NSAIDs, as well as in NSAIDs-induced placebo responses.
Definition: An independent variable is the variable that is changed or controlled in a scientific experiment. Independent variables are the variables that the experimenter changes to test their dependent variable.
Another definition is the organized body of knowledge concerning  the physical world, both animate and inanimate, and the attitudes  and methods through which this body of knowledge is formed..   Science is the systematic study of nature.