This paper examines a patient with borderline mental capacity, where the healthcare team is conflicted about how to proceed. This case demonstrates the complicated intersection between undue influence and mental capacity, allowing us to explore how the law is applied in clinical practice. Patients have the right to decline or accept medical treatments offered to them. In Singapore, family members perceive a right to be involved in the decision-making process for sick and elderly patients. Elderly patients, dependent on mainly family members for care and support, sometimes submit to their overbearing influence resulting in decisions that fail to protect the patients’ own best interests. However, the clinicians’ own well-intentioned influence, driven by a desire for the best medical outcome can also be undue, and neither influence should seek to be a substitution for the patient’s decision. Following Re BKR [2015] SGCA 26, we are now obliged to examine how mental capacity can be affected by undue influence. A lack of capacity can be found when a patient fails to appreciate the presence of undue influence or is susceptible to undue influence due to their mental impairment causing their will to be overborne. This then paves the way for the health care team to decide based on best interests, because the patient is determined to be lacking in mental capacity.