We compare the ability of two social psychological models to explain self-regulation decisions to control hypertension by 208 patients at a hospital clinic: the theory of planned behaviour (TPB) and the model of goal-directed behaviour (MGB). The sample was drawn from patients at a large research hospital in North America. The findings show that the MGB not only explains significantly more variance in decision making than the TPB, but it provides an account for how reasons for acting become integrated and transformed into intentions to act, which the TPB does not address. The MGB does this in part by introducing the variable, desire, as an essential mediator between reasons for acting and intentions. The MGB also incorporates the effects of anticipated emotions on decision making, which are forms of forward-looking counter-factual thinking with respect to goals. In addition, the present study reconceptualized instrumental behaviour to encompass how hard one tries to act in the senses of (1) devoting time to planning with respect to reducing/maintaining blood pressure, (2) expending mental/physical energy to reduce/maintain blood pressure, (3) maintaining will power to reduce/maintain blood pressure, and (4) sustaining self-discipline (e.g. in overcoming obstacles) to reduce/maintain blood pressure. Key differences, as well as commonalities, in decision making are pointed-out between men and women and between people whose goal is to reduce versus maintain blood pressure.