Which of the following is a contraindication for using phentermine/topiramate?

The use of phentermine/topiramate is contraindicated in patients who are concurrently using monoamine oxidase inhibitors (MAOIs). This is due to the potential for significant drug interactions that can lead to hypertensive crises or other serious cardiovascular effects. MAOIs influence the metabolism of various neurotransmitters, and combining them with stimulants like phentermine can exacerbate these processes, leading to dangerously elevated blood pressure and other complications.

In contrast, obesity is the condition this medication is intended to treat, so it is not a contraindication. Hypotension, while a concern, does not specifically contraindicate the use of this combination medication; in fact, the medication might be used with caution in patients with low blood pressure but would require careful monitoring. Therefore, the concurrent use of MAOIs stands out as a clear contraindication for the safe use of phentermine/topiramate.