Final answer:
Out of the list of medications, Metformin is the one least likely to contribute to the fall risk of an elderly woman living in a care facility due to its lack of sedative side effects.
Step-by-step explanation:
An 80-year-old woman living in a long-term care facility has had 3 falls since admission 2 months ago. Out of the listed medications, Metformin is least likely to contribute to her fall risk. Diazepam, Benadryl, and Risperidone are known to increase fall risk in elderly patients due to their sedative properties and possible side effects on motor control and balance. Sertraline, while being an antidepressant that can potentially cause dizziness or imbalance, is generally considered to be less sedating and hence less likely to contribute to fall risk when compared to the others. However, Metformin, which is used to manage diabetes, does not typically have sedation or major effects on balance as side effects, making it the least likely to contribute to her risk of falls.