Which of the following is not a side effect of terbinafine?

Terbinafine is an antifungal medication commonly used to treat fungal infections such as athlete's foot, nail fungus, and ringworm. When considering its side effects, it's important to note that nausea, vision changes, and persistent diarrhea are recognized side effects of the drug.

Nausea can occur as a result of gastrointestinal irritation or sensitivity to the medication. Vision changes, though less common, can sometimes occur and may be related to the drug's effects on the ocular system or neurological pathways. Persistent diarrhea is also documented as a possible adverse effect, often related to disruptions in the gastrointestinal flora or irritation from the medication.

Weight gain, on the other hand, is not typically associated with terbinafine. In fact, weight changes are not a common or well-documented side effect of this medication, which makes it the correct answer in determining which option does not represent a side effect of terbinafine. Understanding this context about the medication helps clarify why weight gain stands out as an unlikely adverse reaction compared to the more commonly reported effects.