BACKGROUND: Multimorbid patients with hypertension experienced treatment burden from managing multiple chronic conditions. Although treatment burden can adversely affect self-care, several qualitative studies have suggested a complex relationship between the two factors. This study aimed to identify patient groups based on the level of multimorbidity treatment burden and self-care adherence and explore factors associated with these patient groups. We also examined if patients transitioned to a different group over six months and which factors were associated with either transitioning into or remaining in the ideal group (Lower burden with higher self-care) at six months. METHODS: This longitudinal study included hypertensive patients with at least two comorbidities (n = 484); 302 participants completed the 6-month follow-up. Patients were categorized into four groups based on multimorbidity treatment burden and self-care adherence levels: All-low (13.8%); Lower burden with higher self-care (26.0%); Higher burden with lower self-care (35.3%); and All-high (24.8%) groups. Multinomial logistic regression was used to explore factors associated with group membership, with the Lower burden with higher self-care group as the reference group. Binary logistic regression was used to explore factors associated with transitioning into or remaining in the ideal group at six months. RESULTS: Older age, higher levels of health literacy, better subjective cognitive function, and greater shared decision-making decreased the likelihood of being in the All-low group. Lower depressive symptoms and higher subjective cognitive function decreased the likelihood of being in both Higher burden with lower self-care and All-high groups, while older age and greater shared decision-making were only associated with the Higher burden with lower self-care group. Patients in the All-low and All-high groups frequently transitioned to another group over six months, while the other two groups remained stable. At six months, participants who were male and had higher health literacy, better subjective cognitive function, and greater involvement in shared decision-making were more likely to belong to the ideal group. CONCLUSIONS: Our study observed the complex relationship between multimorbidity treatment burden and self-care adherence in multimorbid patients with hypertension. Interventions aimed at improving shared decision-making considering patients' circumstances (e.g., emotional status) may alleviate treatment burden and enhance self-care adherence.