Choice A rationale:

Dry mouth is a common side effect of many medications, but it is not a distinctive side effect of SNRIs (Serotonin-Norepinephrine Reuptake Inhibitors). Dry mouth is more commonly associated with medications that affect salivary gland function, such as anticholinergic drugs.

Choice B rationale:

Weight loss can indeed be a side effect of SNRIs. These medications can impact appetite and metabolism, leading to weight loss in some individuals. However, it is not the most common or distinctive side effect when compared to other options.

Choice C rationale:

Constipation is a side effect that can occur with SNRIs, but it's not as prevalent or characteristic as some other side effects. Constipation is often associated with medications that have anticholinergic effects, which SNRIs generally have to a lesser extent.

Choice D rationale:

(Correct Choice) Insomnia is a well-known side effect of SNRIs. These medications can affect sleep patterns and may cause difficulties falling asleep or staying asleep. This side effect is particularly relevant to discuss with patients because it can impact their quality of life and overall well-being.