Mirtazapine for Dogs: Uses as Appetite Stimulant & Dosage

See your vet immediately if your dog has trouble breathing, collapses, has tremors, severe agitation, repeated vomiting, a racing heartbeat, or seems suddenly disoriented after taking mirtazapine. Those signs can point to overdose, a serious drug interaction, or another urgent medical problem.

This article is educational only. Mirtazapine is a prescription medication used off-label in dogs, and the right dose depends on your dog's weight, liver and kidney function, heart health, and the reason appetite is poor. Never start, stop, split, or change this medication without guidance from your vet.

Loss of appetite is a symptom, not a diagnosis. Mirtazapine may help some dogs eat, but it does not fix the underlying cause. Your vet may recommend this medication alone or as part of a broader plan that can include anti-nausea medication, fluids, pain control, diet changes, or testing.

Mirtazapine is a human antidepressant that vets also use in dogs to help with poor appetite and, in some cases, nausea. In veterinary medicine, it is usually prescribed as an off-label oral medication, which means it is not FDA-approved specifically for dogs but is commonly used when your vet believes it fits the situation.

The drug affects serotonin and other brain signaling pathways involved in appetite, nausea, and vomiting. In practical terms, some dogs seem more interested in food within hours of a dose, while others need a little longer or need the medication paired with treatment for the underlying problem.

Mirtazapine is available most commonly as tablets. A transdermal form called Mirataz is FDA-approved for cats, not dogs, so it is not a routine first choice for canine patients. If your dog cannot take tablets, your vet may discuss other appetite stimulants or a compounded option instead.

Vets most often use mirtazapine in dogs that are eating poorly because of chronic disease, nausea, recovery from illness, or treatment side effects. Common examples include kidney disease, liver disease, gastrointestinal disease, cancer care, and periods of reduced appetite after hospitalization or medication changes.

It can be especially helpful when a dog seems interested in food but will not eat enough, or when nausea is part of the picture. That said, if your dog is vomiting repeatedly, has belly pain, has not eaten for more than a day, or is losing weight, your vet may want testing before relying on an appetite stimulant.

Mirtazapine is one option, not the only option. Depending on the cause, your vet may instead recommend or add capromorelin, maropitant, ondansetron, pain control, fluid support, syringe-free nutrition strategies, or a therapeutic diet. The best plan depends on why your dog is not eating.

Mirtazapine dosing in dogs is usually based on weight bands, not a one-size-fits-all schedule. A commonly cited veterinary dosing guide is: 3.75 mg by mouth every 24 hours for dogs under 7 kg (15.4 lb), 7.5 mg every 24 hours for dogs over 7-15 kg (15.4-33 lb), 15 mg every 24 hours for dogs over 15-30 kg (33-66 lb), and 30 mg every 24 hours for dogs over 30 kg (66 lb), with no more than 30 mg per dog. Your vet may use a lower dose or a longer interval in dogs with kidney or liver disease.

Because tablets may need to be split into small portions, dosing errors can happen easily. Use the exact tablet strength and directions your vet prescribes. Do not substitute a human household prescription, and do not assume a cat dose or cat transdermal product is appropriate for a dog.

The oral form can usually be given with or without food. If your dog vomits when it is given on an empty stomach, ask your vet whether future doses should be given with a small meal. If you miss a dose, give it when you remember unless it is close to the next scheduled dose. Do not double up.

Many dogs tolerate mirtazapine reasonably well, but side effects can happen. The most commonly discussed concerns are sleepiness or sedation, restlessness, vocalizing, agitation, increased heart rate, and digestive upset. Some dogs seem more affectionate or clingy, while others act unsettled.

Call your vet promptly if you notice pacing, panting, trembling, marked hyperactivity, diarrhea, repeated vomiting, or unusual behavior after a dose. These signs may be mild side effects, but they can also overlap with overdose or serotonin syndrome, especially if your dog takes other behavior or pain medications.

Dogs with liver disease, kidney disease, or heart disease may need closer monitoring because the drug can last longer or affect them differently. If your dog seems too sleepy to eat, or the medication does not improve appetite, your vet may adjust the plan rather than increasing the dose at home.

Mirtazapine has several important drug interactions. The biggest concern is combining it with other medications that affect serotonin, because that can raise the risk of serotonin syndrome. Examples can include MAO inhibitors such as selegiline, some flea and tick products containing amitraz, certain behavior medications, trazodone, tramadol, and some anti-nausea or pain medications.

Sedating medications can also change how your dog responds. If your dog already takes gabapentin, trazodone, opioids, sleep aids, or other centrally acting drugs, your vet may want a lower starting dose or a different option. Always tell your vet about supplements too, including CBD products and calming chews.

Do not start mirtazapine from an old prescription or from a human family member's bottle. A safe plan depends on your dog's full medication list, recent lab work, and the reason appetite is poor.