# A Review of Medication Adherence Monitoring Technologies +
## 2 Background
### Medication Adherence Monitoring  
Full adherence to medication is required as the drug can be effective only when it is taken [22]. Nonetheless, maintaining strict medication adherence is required that deems maintaining administration timing, dosage quantity, and frequency [28]. A wealth of reports revealed that up to 50% of the patients either never fill their medication prescriptions or do not use the medication as prescribed to them in medication regimens [8; 27; 29; 30; 31; 32]. Unfortunately, poor adherence is prevalent among populations with chronic illnesses [18; 33; 34], which leads to hospital admission [35]. In the US alone, poor medication adherence results in more than 100,000 mortalities annually, as well as hundreds of billion dollars of healthcare spending every year [36; 37; 38]. A number of approaches have been used for the aim of monitoring medication adherence because it has been shown that improving adherence to medical therapy would substantially lead to both health and economic benefits [8].  
In general, two key factors should be considered when discussing medication adherence. The first factor is monitoring, which is alternatively referred to as assessment, quantification, measurement, or evaluation. Medication monitoring means using some methods for observing if the patient has taken the medication or not. Hence, the effectiveness of the monitoring method plays a central role. The second factor is intervention. Interventions refer to the means that can be used for improving adherence to medication or correcting it once erroneous or drift is detected. However, the latter is more in the domain of the psychological and social sciences as it requires understanding the cultural, psychological and social factors that affect the patient's behavior [39; 40; 41], and thus it is out of the scope of this paper.  
Methods that have been utilized for measuring medication adherence so far can be broadly divided into two categories, direct and indirect [8; 42]. Direct methods of measurement of adherence include direct observation of the patient while taking the medication, laboratory detection of the drug in the biologic fluid of the patient (i.e., blood or urine), laboratory detection of the presence of nontoxic markers added to the medication in the biologic fluid of the patient, and laboratory detection of the presence of biomarkers in the dried blood spots [43]. Meanwhile, the patient's self reporting, pill-counting, assessing pharmacy refill rates, and using electronic medication event tracking systems are examples of indirect methods of measuring adherence. There is not a gold standard measurement system that fulfills the criteria for an optimal medication adherence monitoring. Each category comes with benefits and limitations at the same time. Direct measures are accurate, but they may require invasiveness, and they are usually expensive. In comparison, indirect methods are less expensive and provide good estimation of the medication adherence. However, these methods relay on the reliability of the user [44]. As such, these factors should be taken into consideration when selecting the adherence measurement methodology.