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Mirtazapine is an oral medication primarily used for treating depression along with sleep disturbance and anxiety. Additionally, its anti-emetic and appetite stimulant properties might be useful for managing nausea and loss of appetite associated with chronic kidney and liver diseases, intestinal disease, diarrhea, constipation, and pancreatitis, as well as in the treatment of cancer in anorectic cats and dogs [1, 2, 3]. It may also be prescribed for appetite loss associated with IBS, along with other medications like the steroid prednisolone [5].
Another prescription use may be for treatment of inappropriate urination and renal failure in elderly cats, and to control stress in those suffering from interstitial cystitis [4].
Although it is not registered for use in cats by the FDA, it might be prescribed by vets as an extra-label prescription medication [4]. A clinical trial has shown its effectiveness in cats with kidney disease when administered along with proper dietary management.
Quick Information |
|
 Mirtazapine for Cats |
Generic name: Mirtazapine [1]
Brand name: Remeron® [1] Type: Tetracyclic antidepressant [1, 3] Active ingredients: Mirtazapine USP [6] FDA approved: No [4] Availability: Prescription drug [4] Who is it used for: Dogs, cats, humans [1] Available form: Tablets (15, 30, 45 mg), transdermal gel (ranging from 18.7mg/ml – 75mg/ml) |
Mirtazapine, with its anti-nausea property, acts on the intestinal neuroreceptors and prevents them from sending a signal to specialized cells (5-HT3 receptors) in the brain associated with the vomiting reflex [1]. It promotes secretion of the chemicals norepinephrine (important for emotions, dreaming, sleeping, and learning) and serotonin (relaxes the mind and regulates appetite) in the brain, helping in reducing depression [1]. At the same time, it prevents serotonin activity in the GI tract and acts as an appetite stimulant if your cat is not eating properly [1].
Stick to the dosage as prescribed by the vet. The commonly recommended dosage according to the cat’s body weight is:
| Cats by weight | Dose |
| Small Cats (below 15 lb) | 1.875 mg (given once every 72 hours, with/without food) [4] |
| Large Cats (over 15 lb) | 3.75 mg (given once every 72 hours, with/without food) [4] |
For minimizing the chances of overdose, the pills are generally divided into the exact prescribed doses by medical suppliers [9].
Mirtazapine may start working within the first 1 or 2 weeks with improvements in appetite, sleep, and energy. Once these physical symptoms start improving, your vet will know that the drug is working and might tell you to continue administering the prescribed dose for 6 to 8 weeks to improve other symptoms like depression and loss of interest in activities [7].
If you miss a dose, give it as early as possible; but if it is time for its next dose, then give only that [11].
While it does not cause any side effects in most cases, drowsiness is reported in some cats [4]. One potential complication is the serotonin syndrome, occurring due to extremely high serotonin levels in the brain, characterized by dilated pupils, elevated body temperature and blood pressure (dull coat, increased urination, vomiting), increased heart rate, shivering, and general hyperactivity [8]. However, it takes a combination of multiple serotonin-increasing drugs to cause such serious effects.
In a recent study, different doses were given to 84 cats. The ones that received doses higher than what is normally prescribed showed the following adverse effects:
So, contact the vet if you notice or suspect any of the above in your cat.
Inform your veterinarian about any health issues affecting your cat. Mirtazapine should not be administered to cats that are pregnant or nursing [1]. Moreover, dosing may need to be reduced in cats with kidney or liver disease in case there is a chance of serious complications [1].
Mirtazapine may cause drug interactions and should be used with caution in cats that are receiving Monoamine Oxidase (MAO) inhibitors like Amitraz and Selegiline, and Selective Serotonin Reuptake Inhibitors (SSRIs) like fluoxetine (Prozac®) [1].
