BACKGROUND: The number of frail older people is increasing. To alleviate poor health and improve quality of life, pre-frail and frail older people need to adhere to their medication. Yet, studies examining the connection between social capital (including six dimensions) and medication adherence are currently scarce. Therefore, this study aims to examine their relationship in older individuals with pre-frailty and frailty, respectively. METHODS: Information concerning the socio-demographics, frailty, social capital, and medication adherence of 4218 participants was collected through a structured questionnaire during November and December 2020. This study employed descriptive analysis and binary logistic regression to fit their relationship. RESULTS: Among the pre-frail respondents, those with lower social participation (AOR 0.55 [95% CI 0.44-0.69]) had less risk of inadequate medication adherence
while lower social connection (AOR 1.91 [95% CI 1.54-2.36]), lower trust (AOR 2.80 [95% CI 2.25-3.47]), lower cohesion (AOR 2.04 [95% CI 1.65-2.53]), and lower reciprocity (AOR 2.32 [95% CI 1.87-2.88]) were all related to higher odds of inadequate medication adherence. Also, lower social participation (AOR 0.54 [95% CI 0.40-0.74]) was linked to less risk of inadequate medication adherence, while lower trust (AOR 1.89 [95% CI 1.41-2.54]), lower cohesion (AOR 1.68 [95% CI 1.24-2.26]), and lower reciprocity (AOR 1.52 [95% CI 1.14-2.04]) were all found to have a greater odds of inadequate medication adherence in frail respondents. CONCLUSION: By enhancing the relationship between social capital and medication adherence in this challenging community and offering educational programs that promote medication adherence from the perspective of social capital, our findings emphasize the relevance of social capital in improving medication adherence in later life, especially for frail and pre-frail older adults.