Background: China rolled out the national essential medicines policy (NEMP) in primary care in 2009 and led to some unintended consequences including unavailability of essential medicines. This study examined patients’ coping behaviors to these unintended consequences of NEMP as well as the potential impact on primary care system development in Hangzhou, a developed city of China. Methods: We conducted qualitative interviews and surveys with service users, primary care physicians (PCPs), and specialists in tertiary hospitals. Qualitative findings informed the design of the survey questionnaires. Main outcomes included patients’ coping behaviors after the NEMP implementation, as well as providers’ perceptions of NEMP’s impact on primary care development. Thematic analysis of the qualitative data and descriptive analysis of the survey data were conducted. Results: Unintended effects of NEMP included frequent unavailability of certain essential drugs, leading to patient flow from primary care to hospital outpatient clinics for drug refills, difficulties in the provision of continuing care in primary care, as well as compromised patient trust in PCPs. In total, 1248 service users completed the questionnaires. A total of 132 (10.6%) were aged 60 years or above. Among 153 (57.7%) of the 265 who had some chronic condition(s) and needed long-term medication treatment, 60.1% went to hospitals for refills. Four-hundred sixty PCPs and 651 specialists were recruited. Among 404 PCPs who were aware of the NEMP policy implementation in their facility, 169 (41.8%) reported that there was often a shortage of drugs at their facilities and 44 (10.9%) reported always. Moreover, 68.6% of these PCPs thought that the NEMP could not meet their patients’ needs. Further, 44.2% (220/498) of specialists who were aware of the NEMP policy in primary care reported that they often heard patients complaining about the policy. In total, 53.1% of PCPs and 42.4% of specialists disagreed that NEMP helped direct patient flow to community-based care. Conclusion: NEMP’s unintended effects undermined patients’ utilization of primary care in a developed city in China and led to unnecessary hospital visits. Countermeasures are needed to mitigate the negative impacts of NEMP on the primary care system.