The worldwide asthma prevalence is estimated to be 150 million and is increasing in most developed countries. This review examines evidence for the burden of illness caused by nonadherence in asthma, reasons for nonadherence, and the effectiveness of interventions to improve adherence. Evidence consistently suggests that adherence to asthma medicines (particularly inhaled medicines) is poor in adults and children, e.g. adherence to inhaled corticosteroids (ICS) is often <50%. Adherence to prophylactic medicines has been shown to reduce morbidity and mortality. Poor adherence to ICS is linked particularly to poor outcomes in adults, children, and adolescents, including increased hospitalization and mortality rates. Non-adherence in asthma may be linked to patient characteristics such as age, educational level, and socioeconomic status but is more significantly affected by views about asthma as an intermittent and trivial disease, beliefs that ICS do not work and have too many adverse effects, problems with inhaled preparations, lack of social support, cost of prescription medicines, and poor patient-provider relationships. There have been many interventions to improve adherence in asthma. Interventions have largely concentrated on educating patients and have shown variable effectiveness. The most effective interventions are those that promote sustained behavior change. This may involve more acceptable regimens, removing financial barriers, changing misguided beliefs about the illness and the medicines, empowering patients to self-manage their asthma, improved patient-provider relationships, and support from patients' peers. Also, different parts of the population have different concerns about their asthma management, and so interventions need to be sensitive to the age, ethnicity, and socioeconomic status of the patient. Importantly, the benefits of adherence to effective asthma medication can only be realized if appropriate prescribing takes place, hence these interventions need to be carried out alongside evidence-based prescribing. Clinical practitioners need support in their management of people with asthma in both prescribing and supporting adherence. Asthma management is based on a complex set of strategies, promoting the use of regular inhaled preventative medication when the patient is symptom-free. Essential to effective intervention is a non-judgmental environment to encourage provider-patient communication about the patient's knowledge, concerns, barriers, and motivation to adhere.
