Which of the following medications is NOT typically associated with weight gain?

Zonisamide is an anticonvulsant medication that is also used in the treatment of obesity. Research has shown that it can actually be associated with weight loss rather than weight gain, which sets it apart from the other medications listed.

In contrast, thiazolidinediones, sulfonylureas, and insulin are known to promote weight gain as a side effect. Thiazolidinediones, commonly used for type 2 diabetes, can lead to fluid retention and an increase in fat tissue. Sulfonylureas stimulate insulin release and can lead to weight gain due to enhanced glucose uptake by cells and potential stimulation of appetite. Insulin therapy also often results in weight gain because it facilitates the entry of glucose into cells, which can lead to increased fat storage if not matched with caloric intake.

Thus, the unique profile of zonisamide as a medication that can aid in weight management makes it the correct answer in this context.