We report the cases of two patients who developed worsening behavioural and psychological symptoms of dementia (BPSD), coinciding with starting the factor Xa inhibitor direct oral anticoagulant medications apixaban and rivaroxaban, respectively. Both patients required detaining under the Mental Health Act. Their symptoms improved significantly, within 2 weeks, on switching to alternative anticoagulant therapies and they were both discharged from the acute psychiatric ward. Front-line staff should partake in postmarketing surveillance of medications, completing the Medicines and Healthcare products Regulatory Agency yellow cards for example (UK). There is increasing evidence for an aetiological role of cerebral mitochondrial dysfunction in neuropsychiatric disorders. Development of a rating scale of drugs that are potentially less toxic to cerebral mitochondria could inform national prescribing guidelines and enable safer treatments to be offered to older people, reducing the likely hood of them experiencing apparent BPSD.