The extended common-sense model of self-regulation (eCSM) provides a framework by which we can work to gain valuable insights from patients to understand how their illness perceptions and beliefs about medicines impact their treatment-related behaviours. These can be addressed by using behavioural science principles to effectively improve adherence and optimise patient outcomes.

The common-sense model of self-regulation (CSM) is a dynamic framework which seeks to explain the processes by which beliefs about illness impact on behaviour. The CSM proposes that in response to a health threat, such as a medical diagnosis, people construct cognitive representations of their illness (illness perceptions) based on internal cues, such as symptoms, and external cues, such as information from a clinician. The CSM proposes that behaviours to cope with an illness are driven by illness perceptions. The coping behaviour is then evaluated and adapted based on its apparent success.

Studies applying the CSM in a range of health-related behaviours provided empirical evidence to support the role of illness perceptions as predictors of health-related behaviour, however, there is less support for the application of the CSM to treatment-specific behaviours. Studies applying the CSM to adherence to prescribed medication in chronic conditions found only weak associations between illness perceptions and adherence behaviour. This suggests illness perceptions alone are not the best, or only, predictors of treatment-related behaviour.

The ability of the CSM to explain treatment-related behaviour may be increased by taking patients’ beliefs about treatment into account. For example, decisions to initiate, persist and adhere to medication are better explained by both illness perceptions and beliefs about medications.

Beliefs about medications can be grouped into beliefs about medicines in general (such as the belief that doctors over-prescribe medications or that medicines can be harmful) and beliefs about specific, prescribed medications (beliefs about the necessity for treatment and concerns about the potential adverse effects of a medicine). People with negative beliefs about medicines in general are less likely to adhere to medication. Patients with doubts about the necessity for treatment, or strong concerns about adverse effects, are more likely to decline treatment or be non-adherent.

The eCSM includes specific and general beliefs about treatment to increase the ability of the CSM to explain treatment-related behaviours. According to the eCSM, adherence will depend on whether a person perceives their illness warrants treatment, based on their illness perceptions, and whether they believe they have been prescribed appropriate treatment, based on their general and specific beliefs about the treatment. Uptake, adherence and persistence to medication is likely to be influenced by patients’ beliefs about treatment, as well as their illness perceptions. We must therefore use behavioural science to target both illness perceptions and beliefs about treatment to optimise patient outcomes.