On the one hand, while some of these factors may indeed be considered as true confounders, that is, affecting both the exposure and the outcome of interest, and may have led to an overestimation of the main association measured (eg, obesity, a risk factor for breast cancer, may motivate the prescription of a more weight-neutral but prolactin-increasing antipsychotic), other factors may also have led to an underestimation. This evidence concerns the gene PRL and breast carcinoma.