Unequal access to medicines is a universal problem for health-care system reforms (Kolasa and Kowalczyk, 2016). It exacerbates a phenomenon well documented in the literature that people from lower income and minority groups experience higher health risks and are more vulnerable to medication costs (Fu et al., 2020; Pinto et al., 2020). The full coverage policy for medicines (FCPMs) is a policy strategy to promote equal access and adherence to medicines. Depending on specific contexts, FCPMs may also be known as “free,” “full reimbursement,” or “fee exemption” medicine policy. According to the Pharmaceutical Country Profiles by the World Health Organization, all 105 listed countries had implemented FCPMs to some extent. Among these countries, 54 had full coverage programs for any essential medicines (Wang et al., 2019). FCPMs is also increasingly studied and implemented in hypertension and diabetes interventions in the United States (Zheng et al., 2017; Ross-Degnan et al., 2020), Canada (Laba et al., 2020), Brazil (Emmerick et al., 2020), Spain (Puig-Junoy et al., 2016; Gonzalez et al., 2017), Madagascar (Garchitorena et al., 2017), India (Bose and Dutta, 2018), and Burkina Faso (Yaogo, 2017).

China has adopted FCPMs for antihypertensive and hypoglycemic medicines. By the end of 2020, 16 provinces had selected at least one district/county as the pilot area(s) to explore various policy strategies to manage hypertension and diabetes (Yu et al., 2013; Chen and Pan, 2019; Wang et al., 2019; Gong et al., 2020). In 2011, Taizhou, Zhejiang, was among the first cities to implement the full coverage policy for essential medicines (FCPEMs). The policy was set out to be as follows: 1) all nine districts/counties administered by Taizhou city were required to develop a full-coverage medication catalog between 2012 and 2013, specifying what medicines for hypertension and diabetes listed in the National Essential Medicines List of China (version 2012) would be covered in full. 2) Eligible patients could access medicines listed in this catalog without any costs, including drug, prescription, and related medical costs, at any primary care or designated facilities. 3) Physicians at primary care and designated facilities were responsible for evaluating selected medicines’ clinical benefits and appropriateness for patients, and adjusting the medication plan if clinical outcomes were poor. 4) As part of the basic public health services, China had been establishing health records and providing free chronic disease management services for every patient with hypertension and diabetes from the new healthcare reform in 2009 (Li et al., 2017; Lai et al., 2021). All hypertension and diabetes patients using medicines covered must be enrolled in chronic disease management services and have their medication and disease management plan incorporated into health records.

Studies indicated that FCPMs and FCPEMs could reduce medicine-related costs for patients, improve affordability and accessibility of covered medicines, and promote medication adherence (Choudhry et al., 2011; Kolasa and Kowalczyk, 2016; Wang et al., 2019). It can also help with disease prevention and control (Yu et al., 2013) and help in achieving more economical benefits for the society (Ito et al., 2015). There is emerging evidence that implementation of FCPMs and FCPEMs would favorably benefit vulnerable populations in accessing medications (Yu et al., 2013; Kolasa and Kowalczyk, 2016; Gonzalez et al., 2017; Yaogo, 2017), though this is better supported by further investigations. Therefore, we aimed to analyze the change in medication adherence before and after the implementation of FCPEMs in Taizhou and to explore the policy’s effects on income-related inequality in its first years’ implementation.

This study examined income-related inequalities in medicine adherence using a retrospective longitudinal study design and a sample of patients with hypertension or diabetes in Taizhou, China. We identified that FCPEMs promoted overall medication adherence and favorably benefited patients from the low-income group over patients from other income groups.

Our study results are consistent with similar studies in a sense that medication adherence among patients improved after the implementation of FCPEMs and that largest improvement was observed in low-income population. With an increasing proportion of patients taking covered medicines by each year, medication adherence of the general population improved. In other studies of FCPMs, low-income patients who converted from poor to high medication adherence contributed to an increase of 7.8% in medication adherence to statins (Gonzalez et al., 2017) and increased twice more than the high-income patients with diabetes (Ross-Degnan et al., 2020).

Although the income-related inequality in medication adherence did not show consistent improvement over the follow-up period, FCPEMs was effective in improving the inequality in medication adherence. Over the study period, the inequality of medication adherence improved in the first 2 years, but the outcome was conversed in the latter 2 years. In this process, FCPEMs helped in mitigating the changes of inequality. As two studies showed, FCPMs for cardiovascular disease and cancer reduced racial and ethnic disparities in medicines between white and non-white patients after an episode of myocardial infarction (Choudhry et al., 2014; Cole et al., 2020). For the exacerbated inequality, income group (high) was still the greatest barrier to realize equality, and FCPEMs became a positive element against it. As many studies suggest, medication non-adherence is significantly associated with low income (Sunny et al., 2020; Riley et al., 2021). Our study shows that FCPEMs could be a protecting factor against this income-related inequality in medication adherence experienced by low-income patients with hypertension and diabetes. This echoes a Targeted Poverty Alleviation program in China demonstrating that FCPMs could protect low-income patients against heavy burden of medicine costs (Chen and Pan, 2019).

However, due to the comprehensive impact of various factors, FCPEMs not always favorably benefited low-income patients. In our study, we knew change in CI of FCPEMs was the main contributor. The proportion of patients taking free medicines of different groups was thus the key to achieving sustainable equality in access and adherence to covered medicines. However, factors contributing to uptake of free medicines varied. One study showed that lower medication adherence among patients from high-income groups could result from a mismatch of free medicines with their health needs (Marsicano et al., 2015). Another study showed that age was a promoting factor for the uptake of free medicines; 40% of the older adults used free medicines to ameliorate their burden of medicine costs (Tavares et al., 2016). In this study, we found that the uptake of free medicines might be positively associated with an increase in free medicines covered by the catalog (Supplementary Appendix Table S1). We can reasonably conclude that the more health needs the medicines covered under FCPMs could meet, the more likely FCPMs could improve inequality in accessing and adherence to medicines. The geographical accessibility of designated health facilities (Emmerick et al., 2017), qualification of health professionals and pharmacists at these facilities (Zombre et al., 2017; Varas-Doval et al., 2020), and support from families and social networks (Tavares et al., 2016; Zhou et al., 2021) were also critical factors to consider.

It is also worth noting that long-term longitudinal data are necessary for evaluating the inequality in medication adherence and revising the FCPMs programs accordingly. If we only used 1-year data in this study after FCPEMs, the results and conclusions would be different or opposite. Meanwhile, medication adherence is influenced by many factors, thus it would need a comprehensive reform to improve inequality (Fosse-Edorh et al., 2015; Kolasa and Kowalczyk, 2016). During the reform, long-term longitudinal data were important for exhibiting the dynamic results (Zombre et al., 2017) and adjust the intervention precisely, such as the FCPEMs and FCPMs. All these highlighted the value of 4-year longitudinal data used by this study.

Nevertheless, our study has several limitations. First, the prevalence of hypertension and diabetes among residents registered in the local EMR database was 11.2 and 3.2%, respectively, in 2016, which were lower than the disease prevalence shown by epidemiological data (Li, 2021; Li et al., 2021; Xia et al., 2021). This implies a participant bias and that our sample might not be fully representative of the general population residing in Taizhou. Second, our measurement of the medication adherence was also subject to recall bias and administration bias as health records and follow-up surveys were collected by medical staffs, who might have varying degrees of training in administering surveys. Third, our results might have been affected by missing data and influence factors in the database, such as comorbidities. We made controls for this by aggregating all medical records of a patient within one calendar year into an annual data input. Patients with missing data after data aggregation were excluded from our study. Last, our baseline covered only 1 year as the database for chronic disease management was only established since 2011, and data prior to the year were inaccessible. This study schedule might influence the interpretation of our longitudinal data. However, we identified no other significant policy during local investigations, and our result that FCPEMs was a major driver for improvements in medication adherence still holds.

In conclusion, overall medication adherence of the study population improved after the implementation of FCPEMs in Taizhou, and the low-income population experienced the largest increase in adherence to medicines. Interventions in the future should look into designing an optimal medicine catalog by first investigating the health needs of local residents to promote intervention uptake.