An older woman with dementia and type 2 diabetes was started on semaglutide and subsequently developed severe psychological and physical symptoms, including apathy, significant weight loss and decreased appetite. These symptoms markedly improved after the medication was discontinued. This case underscores the importance of recognising potential psychiatric side effects of semaglutide, especially in older adults with cognitive impairment. The experience highlights the need for careful monitoring when prescribing semaglutide in this population and suggests that discontinuation should be considered if adverse symptoms arise. It also raises awareness about the limited safety data on semaglutide in older patients, emphasising the necessity of further research to understand its effects on this vulnerable group.