Mirtazapine Use in Dogs As an Appetite Stimulant

Mirtazapine is a type of human tetracyclic antidepressant, which can be used in pets as an appetite stimulant. If your pooch isn't eating enough, especially if his lack of appetite is due to a chronic illness, your vet may prescribe this medication. While mirtazapine isn't approved for use in dogs by the U.S. Food and Drug Administration, it can be prescribed "off label" for pets.

Dalmatian Eating Food From Dish
Mirtazapine stimulates your dog to eat and eases his nausea.
credit: IPGGutenbergUKLtd/iStock/Getty Images

How it Works

Mirtazapine helps to stimulate your dog's appetite by increasing the levels of serotonin and norepinephrine in his body. Norepinephrine has a stimulating effect on your dog; serotonin makes him feel calm and relaxed. Together, these neurotransmitters make him feel good and help to stimulate his appetite. The medication also affects how the neuroreceptors of the intestines and stomach process serotonin. While serotonin helps to make your pup feel good, it can make him nauseous if too much of it gets into his digestive system. By keeping the amount of serotonin in his digestive system to a minimum, mirtazapine stops any feelings of nausea.

Administration of Mirtazapine

Mirtazapine typically is prescribed for dogs dealing with appetite loss due to a variety of conditions including intestinal diseases, kidney or liver disease and stomach issues. It can alleviate nausea caused by chemotherapy drugs used to treat cancer. Mirtazapine typically is given to dogs once per day. It's available in 7.5, 15, 30 and 45 mg regular tablets and rapid-dissolve tablets. Your vet will determine the correct dosage for your dog based on his weight. The dose may need to be reduced if he is suffering from liver or kidney disease because these organs help metabolize medications in the body. Other formulations, such as an oral suspension or transdermal gel, can be made by a compounding pharmacy for your pup.

Side Effects and Precautions

Side effects from mirtazapine are usually mild; it can be used long-term to treat your pup's lack of appetite from chronic health conditions. The main effects are drowsiness and sedation. At higher doses, your dog could experience a rapid heartbeat or his blood pressure could drop to a low level. If your dog is allergic to mirtazapine, he could experience facial swelling, hives or trouble breathing. Mirtazapine may cause issues in some dogs with their blood cell development, so your vet may need to monitor your pooch if he suffers from leukemia or a blood disease, according to VeterinaryPartner.com. Discuss the use of mirtazapine in pregnant and nursing pooches with your vet because it may not be safe.

Drug Interactions

Selective serotonin reuptake inhibitors such as fluoxetine and tramadol should not be given with mirtazapine. These and other drugs that increase the amount of serotonin in your pup's brain can cause too high a level of it in his body when given along with mirtazapine, a condition known as serotonin syndrome. Signs of serotonin syndrome include a fast heart rate, trouble breathing, high blood pressure, hyperactivity and shivering, according to the Atlantic Coast Veterinary Specialists. Don't administer monoamine inhibitors along with mirtazapine, including selegiline and some insecticidal dips. Wait 14 days between administering the last dose of a monoamine inhibitor and giving your pooch mirtazapine.