Evaluation of the Short-Term Effects of Mirtazapine on Appetite Stimulants in Dogs: A Retrospective Study and a Placebo-Controlled Trial.

Anorexia and hyporexia are common clinical signs in dogs with acute or chronic illnesses, often requiring targeted nutritional interventions. Mirtazapine, an orexigenic drug widely used in cats, has limited evidence supporting its use in dogs. This study evaluated mirtazapine's efficacy as an appetite stimulant in dogs using a two-part approach: (1) a retrospective analysis of 107 clinical cases comparing dogs that received mirtazapine to untreated controls; and (2) a prospective, placebo-controlled, double-blind crossover trial involving 25 dogs. In the retrospective analysis, dogs treated with mirtazapine were significantly more likely to resume voluntary food intake (OR = 3.06) and had less weight loss compared to controls. In the prospective trial, mirtazapine significantly increased food acceptance on the first day (100% vs. 63.6%, p = 0.03), with no adverse effects observed. However, the effect was not maintained on the second day, possibly due to residual drug activity or clinical improvement. Latency to feeding averaged 120 min post-administration. Mirtazapine was safe and well tolerated, even in dogs with comorbidities. These findings support the short-term use of mirtazapine as a second-line appetite stimulant in dogs when enteral feeding is not feasible.