Overall, the TAI Toolkit showed good usability and potential for larger-scale implementation. Suspicions of non-adherence by HCPs were confirmed by the TAI in over 80% of the patients. Of note, patients varied in terms of demographic and clinical characteristics. Sporadic non-adherence was the most common type of non-adherence identified.

The TAI Toolkit is the first tool of its kind and shows good usability. The need for easy-to-use measurement methods to detect non-adherence and guidance on how to act on the outcome of those measurements has been stressed before10. Indeed, a systematic review identified the TAI questionnaire as one of the best self-report adherence instruments in terms of psychometric quality, accessibility and utility for detecting non-adherence in patients with asthma10. The review also disclosed the TAI Toolkit as the only instrument that has been further developed and used to guide HCPs into the deployment of cause-based and patient-tailored interventions in patients with lung diseases10. All interventions recommended by the TAI Toolkit are evidence-based. The added value of the TAI Toolkit is that it identifies the specific type of non-adherence (sporadic, deliberate, unconscious) and then offers a multifaced tailored intervention. Multifaced tailored interventions can have a significant impact on improving medication adherence compared to usual care in asthma/COPD and in other chronic patient groups, demonstrating the potential impact of the TAI Toolkit for patients using inhalation medication11,12,13,14,15. The potential impact in terms of the reach of the TAI Toolkit is also presented within this study. The estimation of encounters with relevant patients is measured subjectively and varied between the participating study sites. However, the overall high numbers of relevant patients HCPs encounter give an impression of and nuance to the experienced relevance and usefulness of the toolkit. Also, it gives insight into the relevance of the participating study sites and, therefore, the potential settings.

Regarding patient characteristics with suspicion of non-adherence, patients were not only heterogeneous in terms of physical status but also with respect to age, comorbidities and socioeconomic background. However, the overall older population, with multimorbidity and polypharmacy included in this study, is known to be at higher risk for nonadherence16,17,18. Patients’ number of exacerbations was as expected for the general population of both asthma and COPD, but lower than expected looking at the high levels of non-adherence we found in this study19,20,21,22.

Notably, whereas non-adherence in patients with asthma and COPD is estimated to be between 22% and 78%, we found a higher percentage of 81% for complete non-adherence and an even higher percentage in patients with asthma (85.7%)3. This relatively high degree of non-adherence could be explained by the fact that we defined “non-adherence” as not completely adherent (i.e. TAI < 54) in line with other studies using the TAI questionnaire23,24. Another explanation for this high degree of non-adherence is that one of the inclusion criteria was to select patients with a suspicion of non-adherence. However, note that previous studies indicated that HCPs frequently overestimate adherence in their patients25,26.

We found sporadic non-adherence to be the most common type of non-adherence with forgetfulness and misunderstanding of the therapy the most common in both patient groups. In line with previous studies, unconscious non-adherence was more common in patients with COPD, and deliberate non-adherence was more common in patients with asthma23,24. Patients with COPD are often lower educated and of older age compared to patients with asthma (possibly leading to more misunderstanding and forgetfulness), whereas patients with asthma are more likely to be deliberately non-adherent due to more fluctuating asthma symptoms23,27,28. Here, it is important to note that although some non-adherence barriers are patient reported, this does not mean the patient is accountable. For example, inadequate patient knowledge regarding when or how to use the inhaler can also be the result of poor HCP education or communication.

Not surprisingly, when considering the most common causes of non-adherence, the interventions ‘patient education and information’ and ‘link to daily routine’ were the most selected interventions. Also, inhalation instruction was one of the most selected interventions, while inhalation technique failure was not marked as one of the most common causes of non-adherence. That said, even though the TAI Toolkit offers an overview of the causes of non-adherence coupled interventions, HCPs—and the patient—still have the task of detecting what is the most prominent or underlying cause. For instance, when a patient believes medication is not that effective or necessary (conscious non-adherence), he or she may also sooner forget to take the medication (sporadic non-adherence).

Finally, inhalation instruction and patient education are often perceived as usual care when starting or switching inhalation medication, but selecting these interventions when non-adherence was observed could suggest that reinforcement was required.

This study has multiple strengths. First, the TAI Toolkit has been designed with a variety of team members (researchers, nurses, pharmacists and physicians), making the toolkit accessible for different HCPs. Also, the interventions advised by the toolkit have been proven to enhance medication adherence and some have already been implemented in current guidelines29,30, which meant that the interventions could be easily and instantly delivered by the HCPs. Third, the prototype has been tested in a variety of settings (rehabilitation centre/nursing home, hospital and general practice), adding to the generalisability of the results.

There are also some limitations. First, although the prototype has been tested in different settings, all settings were outpatient consultation rooms in a high-income country. Different settings, such as nursing wards and community pharmacies, may be relevant settings as well. Second, the participating HCPs were all specialised to some degree in respiratory medicine and patients were only included during consultations concerning their asthma/COPD. It remains uncertain whether general nurses, pharmacists and physicians (not-specialised in lung care) would be able to use the TAI Toolkit and what the most relevant or crucial moments of encounters are to apply the toolkit.

Third, one of the inclusion criteria was a suspicion of non-adherence. This leads to targeting the right population but possibly also to inflation of the observed percentage of patients that were non-adherent within this study. Also, suspicion of non-adherence is a rather subjective inclusion criterion and depends greatly on the HCP. This inclusion criterion could have led to a selection bias, e.g., patients who felt more connected with their HCP would perhaps feel more comfortable discussing barriers or difficulties with their medication compared to patients who felt less connected and the HCP would sooner find clues for non-adherent behaviour.

Lastly and most importantly, the TAI questionnaire and, therefore, the toolkit do give insight into patients' reported behaviour concerning medication, but there are more underlying factors that play a role. Factors (or causes) that contribute to non-adherence, such as prescription errors (or non-adherence to treatment guidelines by HCPs), availability of the medication and the possibility that the medication simply does not result in the desired treatment effect, are not directly identified by the TAI. When using the toolkit, it is the HCP’s task to not just view the answers and scoring; they are expected to discuss deviants (or lower scorings). Even though our results show that HCPs experience more insight into patients’ behaviour, the effect of a potential intervention is highly dependent on the communication skills of the HCP.

More research is needed that focuses on the different types and causes of non-adherence in lung patients. Moreover, more research is needed to identify the crucial moments, HCPs’ abilities to identify the most prominent cause of non-adherence and if, consequently, the appropriate intervention is applied and effective. With non-adherence also being mentioned generally and non-specifically in the Dutch guidelines for asthma and COPD, if and how non-adherence has been detected and managed currently is unclear31,32. Furthermore, the impact of an intervention does not only depend on whether the (most prominent) cause of non-adherence is targeted but also on the patient characteristics and quality of the application of the intervention itself. Insight into the relevance of interventions for specific subpopulations is desired as well.

For use in clinical practice and the possibility for upscaling, the TAI Toolkit needs to be improved and further developed according to the feedback retrieved in this study; a smaller pocket-size model and a digital version—preferably integrated into electronic patient record software—were desired. In addition, minor adjustments to the content were suggested, such as an overview of all possible involved healthcare professionals and organisations. Because of the longer consultation time of nurses and the more holistic view of the patient within the nursing profession, as mentioned by the HCPs, further development and implementation should focus on the nursing profession. Additionally, the TAI Toolkit should be tested and evaluated in other contexts, e.g. in nursing wards, in other healthcare disciplines and by non-lung specialists to assess the potential for wider implementation.

Secondly, patient-reported measurements such as the TAI are always prone to self-report biases and although the TAI also provides the causes for non-adherence, it is advisable to complement with another objective measurement method such as smart inhaler data or medication refill rates33.

Lastly, evaluating whether and why a patient is non-adherent remains a challenge and the TAI questionnaire and toolkit do not cover all possible factors and causes. Deployment of the TAI questionnaire and the TAI Toolkit should be considered as a low-key routine tool, but HCPs must remain aware of less visible or straightforward causes for non-adherence, such as the possibility the prescribed medication simply does not have a beneficial effect on the patient. Understanding the patient and his or her health behaviour is key to guide patients into more adherent behaviour33. This requires strong communication skills and a relationship of trust between the HCP and the patient. A focus on HCPs’ communication skills and training is needed to tackle the issue of non-adherence and to be able to use the TAI Toolkit properly.

The TAI Toolkit is the first in its kind to combine and connect an adherence measurement instrument to proven effective interventions. The toolkit was deemed feasible for daily practices specialised in chronic lung care and usable for HCPs to structurally acquire more understanding of non-adherent behaviour. Although the effectiveness of the TAI Toolkit was beyond the scope of this research, the TAI Toolkit has the potential to improve suboptimal adherence and clinical outcomes starting by structurally detecting and addressing non-adherence and its causes.