A number of rigorous reviews have found that, in developed countries, adherence among patients suffering chronic diseases averages only 50% (1, 2). The magnitude and impact of poor adherence in developing countries is assumed to be even higher given the paucity of health resources and inequities in access to health care.

For example, in China, the Gambia and the Seychelles, only 43%, 27% and 26%, respectively, of patients with hypertension adhere to their antihypertensive medication regimen (3 - 6). In developed countries, such as the United States, only 51% of the patients treated for hypertension adhere to the prescribed treatment (7). Data on patients with depression reveal that between 40% and 70% adhere to antidepressant therapies (8). In Australia, only 43% of the patients with asthma take their medication as prescribed all the time and only 28% use prescribed preventive medication (9). In the treatment of HIV and AIDS, adherence to antiretroviral agents varies between 37% and 83% depending on the drug under study (10, 11) and the demographic characteristics of patient populations (12). This represents a tremendous challenge to population health efforts where success is determined primarily by adherence to long-term therapies.

Although extremely worrying, these indicators provide an incomplete picture. To ascertain the true extent of adherence, data on developing countries and important subgroups, such as adolescents, children and marginal populations are urgently required. A full picture of the magnitude of the problem is critical to developing effective policy support for efforts aimed at improving adherence.

In developed countries, adherence to long-term therapies in the general population is around 50% and is much lower in developing countries.