Evidence in the literature supports the introduction of interventions to enhance adherence to antidepressant therapy, especially in patients with major depression.

The objectives of this study are; (1) to examine patient and population-based research on patient's adherence to antidepressants and (2) to develop and psychometrically assess a four-item instrument to measure adherence to antidepressants.

Although causes for non-adherence are multifatorial, drug omissions could occur in one or more, of main four mechanisms; forgetting, carelessness, stopping the drug when feeling worse, or stopping the drug when feeling better. To our knowledge, no reliable valid instruments were developed to measure adherence to antidepressants. Authors modified an instrument that was developed by (Morisky 1986), to measure adherence to antihypertensive drugs. The modified instrument was distributed to experts in depression (n=12), to rate the instruments’ relevancy, as a measure of patients’ adherence to antidepressants, and was administered to patients (n=63), who are on antidepressants.

The modified instrument has an improved reliability (Chronbachs’ Alpha = 0.66), there is 90 %, overall agreement among experts, that the instrument relevant to measure adherence in outpatients with depression, supporting a strong evidence for content validity, and there is also strong evidence for convergent and criterion related validities.

The developed instrument is short, both reliable and valid, and could be completed in approximately 3 minutes. Although it was developed for with outpatients, it could be applied in different sittings, with wide range of psychiatric population who suffer from depression.