Most breast cancer patients undergoing adjuvant hormonal therapy have difficulty taking medication for several reasons, such as forgetfulness or the symptoms associated with it. Such reasons can have a negative effect on their adherence to medication. The objectives of this study were to develop a medication adherence promotion program based on Cox''s interaction model of client health behavior for breast cancer patients undergoing adjuvant hormonal therapy and to identify its effects on medication adherence, perceived stress, depression, fatigue, and menopausal symptoms.
A total of 79 participants who were receiving adjuvant hormonal therapy were recruited from an outpatient clinic of C hospital, and randomly allocated into experimental (n=44) or control (n=35) groups.
The medication adherence promotion program was designed to represent elements of professional interaction withclientsin Cox''s interaction model. Affective support consisted of telephone call counselling and sending supportive text messagesand mailing postcards. Health information consisted of individual education and sending information pamphlets. Decisional control consisted of counsellingby telephone, a written pledge of health, and sending a medication notification once a week. Professional and technical competencies consisted of having question and answer sessions, and monitoring medication and exercise adherence during 8 weeks. The dependent variables representing elements of health outcome in Cox''s model were medication adherence, perceived stress, depression, fatigue and menopausal symptoms. The effects of the medication adherence promotion program were assessed threetimes (before applying intervention and in the ninth and 16th weeks). The data were collected from July 3 to November 9, 2017.

The results of the study are summarized as follows.
1) There was a statistically significant difference in medication adherence between the two groups. The experimental group reported higheradherence than before the medication adherence promotion program wasapplied,whereasthecontrol group reported gradually decreasing adherence, even thoughthe two groups’medication adherencescores were similar inthe pre-test period.

2) There was a statistically significant difference in perceived stress according to participation in the medication adherence promotion program. The perceived stress of the experimental group decreased in theninth week and increased a little inthe16th week. However, the degrees of perceived stress intheninth and 16th weeks were better than before the program was applied.

3) There was a statistically significant difference in depression according to participation in the medication adherence promotion program. Depression intheexperimental group decreased intheninth week and increased a little inthe16th week. However, the degrees of depression were better than before the programwas applied.

4) Changes in degree of fatigue in the experimental and control groups were not significantly different.

5) There was a statistically significant difference in menopausal symptoms in the psychosocial aspect according to participation in the medication adherence promotion program. The aspect of the experimental group decreased and then increased alittlein the16th week, but the degree was better than before the medication adherence promotion program wasapplied. However, the changes in degree of menopausal symptoms in vasomotor, physical and sexual aspects were not significantly different.

In conclusion, based on the results above, the medication adherence promotion program based on Cox''s interaction model of client health behavior contributed to the improvement of medication adherence and some of the symptoms breast cancer patients had in the course of adjuvant hormonal therapy. Therefore, it is clear that constant individualized nursing intervention is needed, particularly for breast cancer patients who have to take medication for a long time, as there is high probability of lower medication adherence otherwise.