Adherence to medicines has been identified as a key issue by the Royal Pharmaceutical Society of Great Britain, the WHO and, most recently, by the UK Academy of Medical Sciences. Estimates of adherence vary widely but are often reported to be as low as 50%. When a patient does not take their prescribed medicines as intended, they may not derive the expected outcomes. As well as implications for the individual patient, this can result in increased costs associated with patient hospitalisations or avoidable escalation in other costs of care. It may also result in unused medicines, the cost of which is estimated at £300 million per year in England alone.