A study with a placebo was conducted. Healthy university students were given a placebo and were told to make one pill every day for a week. Participants were informed that the medicine improved mood. The extent to which they conformed to this instruction was treated as an index of compliance. Our results show that for women, but not for men, positive mood and cognitive structuring or negative mood and lack of cognitive structuring significantly predicted participants' compliance. A new model of medication adherence, based on the role of the patient's mood and cognitive structuring processes in decision making is presented in the paper.