Depressive disorder is one of the most prevalent forms of mental illness, and is of major public health importance (1). It is characterized by abnormal and persistent low mood, accompanied by other symptoms including sleep disturbance, loss of appetite, suicidal thoughts, impaired concentration and attention, guilt and pessimism. Symptoms vary in severity, and the pattern of illness can range from an isolated and relatively mild episode, through recurrent episodes of moderate severity, to chronic and persistent severe illness. Owing to its prevalence, and to health system factors, primary care practitioners see most of the patients with depression and few are referred to specialist psychiatric services, even when they are readily available.

Although psychological treatments of proven efficacy are available for the management of depression, the most common form of treatment worldwide is antidepressant medication. For patients with a definitive diagnosis of depression, pharmacotherapy guidelines advocate that treatment should continue for at least 6 months following remission of symptoms. Furthermore, for patients who have suffered two or more episodes of significant depression within 5 years, long-term preventive treatment is suggested (2).

The clinical effectiveness of drug therapies for depression is limited by two groups of factors; patient adherence to the recommended protocol, and under-diagnosis and/or suboptimal treatment by primary care doctors. Both groups of factors appear to be relatively common, but the focus here is on adherence. However, the diagnosis and treatment cannot be ignored as they are likely to interact with, or to mediate, adherence.

This chapter discusses research methods, the overall prevalence of adherence, predictors of adherence and the efficacy of interventions designed to improve adherence. A literature search was made using Medline (1990 - 2001). A total of 287 publications were identified and evaluated.