# A Review of Medication Adherence Monitoring Technologies +
## 1 Introduction  
Human lifespans will continue increases as the average quality of life improves. Evidence of this can be seen in recent reports that highlight the significant increase in aging population, especially in developed countries [1; 2; 3]. As one would anticipate, the global population of people aged 60 years and older will grow by 250% in 2050 as compared to 2013 [4]. Likewise, as society ages, long-term healthcare expenditures are projected to increase [5]. In order to maintain a healthy aging population, the employment of Assistive Health Technology (AHT) increases [4]. Based on this, great efforts are being made towards achieving greater expectations of the quality in healthcare systems [3]. There is no doubt that rapid technological advances will revolutionize research in the 21 st century in a number of disciplines; namely human health. New approaches to monitor human health, behavior, and activity will be enabled. Medication adherence is an important component of health and well-being, with voluminous studies showing the importance of adequate medication adherence [6; 7; 8; 9; 10]. Achieving healthy aging is challenging and thus requires several important strategies. Undoubtedly, correct medication is one of these strategies that are mainly related to the individual's behavior. In addition, it is well-known that medications are the primary approach for treating most illnesses [11]. Hence, it requires the individual to take the medication as directed bythe healthcare professional [12]. However, medication adherence remains a common issue within the healthcare sector, and especially among older adults. In fact, more than 50% of the older people are living with multiple chronic illnesses. Thus, routine monitoring and assessment of the individual's adherence is crucial to improve their health outcomes [13]. To be successful, this should be performed using accurate assessment methods. Current assessment methods of medication adherence have advantages as well as limitations. The main objective of the current article is to provide insights into what has been happening with respect to medication adherence monitoring technologies and address open research challenges for further improvement. This review paper includes articles from journals, and conference papers and proceedings. We excluded articles classified as editorials, book reviews, white papers, or newspaper reports. While searching for papers, electronic databases including Google Scholar, IEEE Xplore, ACM Digital Library, Springer Link, MDPI, and Science Direct, were used. The descriptors we used were \"medication adherence\", or \"medication intake\", or \"medication monitoring\", or \"medication compliance\" in combination with at least one of others, including \"technology\", \"sensor\", \"smartwatch\", \"wearable\", \"smart bottle\", \"pill bottle\", \"pillbox\", \"vision system\", \"Radio Frequency Identification (RFID)\" and \"Near Field Communication (NFC)\". The search was inclusive of all years from 2004 through 2018. Using primarily the full text and also the abstracts, we selected articles discussing medication adherence monitoring technologies and excluded papers discussing intervention applications. The literature review approach used in this paper follows an iterative and incremental procedure [14], and hence found and included new studies about medication adherence monitoring technologies and approaches to the surveyed studies. It is worth mentioning that there have been some commercial efforts in the past few years to develop medication adherence monitors, for example [15; 16; 17; 18; 19]. However, we do not include these commercially available systems in this review as they are like black boxes and the information surrounding their design is either not published in any publicly available form or that information can be limited.