Mirtazapine for dogs and cats



Active ingredient



Appetite stimulant / Anti-depressant / Anti-nausea

What is Mirtazapine?

Mirtazapine is a tetracycline (TCA) anti-depressant drug typically used to treat depression in humans. The tablet form is used off-license to treat nausea and stimulate appetite in pets. Occasionally, it is used to treat anxiety in pets too. There are a couple of brand names, but they all contain the same active ingredient. As mirtazapine is a prescription-only medicine and its use is off-license in animals, your vet will need to prescribe mirtazapine for your cat or dog.
Please note there is a licensed version of mirtazapine ointment for cats, called Mirataz.

How does Mirtazapine work?

Mirtazapine is a TCA anti-depressant drug which is mainly used to stimulate appetite and alleviate nausea in pets. Mirtazapine works by increasing the amount of serotonin and norepinephrine in nerves found in your pet’s brain and gut. Mirtazapine also blocks histamine receptors in the brain, which helps to relieve nausea.

What is Mirtazapine prescribed for?

Mirtazapine is mainly used in cats and dogs to stop them from feeling sick and to encourage them to eat food. Your pet could feel sick due to another condition, such as cancer, pancreatitis, and kidney disease. Some of the side effects of other treatments (such as chemotherapy) can also make your pet feel sick and go off their food. Mirtazapine is an anti-depressant drug and is sometimes used to treat anxiety in pets.

Here are some of the reasons your vet may prescribe your pet with mirtazapine:

  • Nausea due to chemotherapy or other drug side-effects
  • Nausea due to other conditions e.g. certain brain diseases or kidney disease
  • Older dogs with a poor appetite
  • Your pet may need to gain weight following surgery
  • Anxiety – this is less common.

Remember, Mirtazapine should always be given under veterinary guidance, ensure to consult your vet so that you can do what’s best for your pet.

What are the side effects of Mirtazapine?

Whilst most pets tolerate Mirtazapine well, there are still side effects to be aware of. The severity of these side effects may depend on the dose of Mirtazapine being given and the overall health of your pet.

The side effects to be aware of may include:

  • Vomiting – It would be useful to take a picture of your pet’s sick so that your vet can assess it further.
  • Poor coordination – Your dog may bump into furniture or struggle to walk steadily.
  • Sleepiness – This would be due to the sedative effects of the dog.
  • Increased urination and dehydration – These side effects commonly occur. Depending on the severity of dehydration, your pet may have to stop taking mirtazapine.
  • Increased saliva – You may notice your pet drooling more in this case.
  • Restlessness – Your pet may seem more agitated than usual and not settle.
  • Skin problems – This can occur with the use of mirtazapine ointment, as the drug is put directly on the skin.
  • Serotonin syndrome – This occurs when mirtazapine is given in combination with other drugs that affect serotonin, such as MAOIs. This syndrome may present as agitation, tremors, increased body temperature and a high heart rate. If this occurs, stop treatment immediately. To be safe, make sure to tell your vet what other medications your dog is on before they give your pet mirtazapine.

Your vet will weigh up the risks of mirtazapine side effects in your pet before recommending it. For most pets, the benefits of using Mirtazapine outweigh these risks. However, if you do notice any of these side effects (or any other!), get in touch with your veterinarian for advice. They will be able to provide you with guidance and adjust the treatment plan if necessary. This will help to ensure your pet’s safety and put your mind at ease. 

Which pets is Mirtazapine not suitable for?

  • Mirtazapine is not suitable for pregnant, breeding, or lactating animals.
  • Mirtazapine is not suitable for pets with kidney disease.
  • Mirtazapine is not suitable for pets with a history of seizures or epilepsy.
  • Mirtazapine is not suitable for pets with a known mirtazapine allergy.
  • Mirtazapine is not suitable for puppies or kittens.
  • Mirtazapine is not suitable for pets on other drugs that affect serotonin, including MAOIs, cyproheptadine and tramadol.

How much monitoring do pets need on Mirtazapine?

  • High monitoring need


    Most pets will not require a vet to monitor them whilst they are on mirtazapine.

You should always monitor your pet for side effects and report any concerns to your veterinarian. Most pets will not require a vet to monitor them whilst they are on mirtazapine. However, there are some instances where your pet does require more monitoring during mirtazapine treatment.

  • For pets with liver disease, blood tests should be regularly done to monitor liver enzyme levels.
  • For pets with kidney disease, bloods should be regularly monitored to check for further kidney damage.
  • For pets with diabetes, blood glucose should be regularly monitored.
  • If your pet has a condition that makes them dehydrated, they may require monitoring for regular supportive fluids.

How to give Mirtazapine safely:

  1. Follow vet instructions: Listen carefully to your vet’s instructions, because they may differ from what’s on the packet. This is because mirtazapine is used off-label. This includes the right dose and frequency. Never adjust the dose on your own, even if your dog or cat seems to be feeling better or worse. If you have forgotten the instructions or aren’t sure of the dose prescribed, please call your vet to confirm.
  2. Give with or after food: It’s safest to give mirtazapine tablets on a full stomach to prevent any digestive upset. You can either put the tablets in a bit of food to tempt your pet, or directly into their mouth after food if they will let you.  
  3. Check with your vet if giving anything else: Your vet should be aware of other drugs your pet is on, but it’s always worth double-checking in case there’s been a miscommunication somewhere. Other drugs that affect serotonin should not be used alongside mirtazapine, such as MAOIs. If your pet is on supplements or non-prescription treatments you should also tell your vet when they prescribe mirtazapine, as they may not be suitable to be given together.
  4. Storage and Handling: Store mirtazapine according to the instructions on the label, usually in a cool and dry place. Make sure it’s out of reach of children and other pets. If you are using mirtazapine as an ointment, make sure to use gloves and wash your hands after use.
  5. Report any accidental overdose to your vet immediately: If you have mistakenly given too much mirtazapine, report it to your vet as soon as you realise the error. They may recommend monitoring or blood tests.

What does Mirtazapine cost?

  • pound

    £ – Inexpensive

    Mirtazapine is usually inexpensive when the tablet form is used.

If your pet needs a tablet form of mirtazapine, then this drug is relatively inexpensive. It’s a human drug, so cats and dogs usually need a small proportion of a tablet. With dispensing or prescription fees, you’re likely looking at £5-15 for a course.

Mirtazapine FAQs

How long does it take for mirtazapine to work for appetite in dogs?

How long it takes for mirtazapine to stimulate appetite in dogs will vary depending on your dog’s metabolism and any other conditions they have. Typically, mirtazapine should start to improve your dog’s appetite within 24 hours. Some dogs will become interested in food again after just a few hours. For extremely unwell dogs, it may take up to 48 hours for it to start working. If you don’t think mirtazapine is improving your pet’s appetite after 48 hours, talk to your vet about the alternatives.

What effect does mirtazapine have on dogs?

The desirable effects of mirtazapine on dogs include appetite stimulation and alleviating sickness. The side effects of mirtazapine on dogs may include vomiting, sleepiness, restlessness, serotonin syndrome, and increased urination. If you are worried about your dog’s side effects, stop giving the medication, and contact your vet.

Will mirtazapine help my dog sleep?

Mirtazapine will not be prescribed to help make your dog sleep. It will be given to improve your pet’s appetite and relieve nausea. In this case, one of the side effects of mirtazapine is drowsiness so it may make your pet sleepy.

Why do you have to wear gloves when applying mirtazapine?

Mirtazapine can be absorbed through the skin, so you should wear gloves when applying the drug to stop this from happening. If you have a known allergy to mirtazapine, avoid handling the drug and let your vet know.

Is mirtazapine an appetite stimulant for dogs and cats?

Mirtazapine is an appetite stimulant for dogs and cats. It works by changing the levels of serotonin in the brain and gut to relieve nausea and improve appetite. This may be helpful in pets with conditions or other treatments that make them feel sick, such as cancer and chemotherapy.

What are the alternatives to Mirtazapine?

If mirtazapine tablets are difficult for you to administer at home, you could consider the licensed ointment version ‘Mirataz’. Cats need a 3.8cm line of ointment rubbing into their ear once a day, and your vet can work out a dog dose if they feel your dog would benefit from Mirataz. If you find that mirtazapine isn’t working for your pet, or they are experiencing severe side effects, there are other anti-sickness drugs available.

Other anti-sickness drugs include:

  • Maropitant (Cerenia, Prevomax) – given as injection or tablets
  • Metoclopramide (Emeprid)
  • Ondansetron (Zofran)

If your pet was given mirtazapine for anxiety but it hasn’t worked out, your vet may try one of the following other anxiety medications:

  • Gabapentin – available as a tablet or liquid.
  • Sileo – available as an oral gel
  • Trazadone – available as a tablet
  • Alprazolam – available as a tablet or liquid.
  • SSRIs e.g. Prozac – available as a chewable tablet
  • Natural supplements – Adaptil and Nutracalm

It is important to remember that you will not be able to buy any anti-sickness medication for your pet over a non-veterinary counter! You will have to go back to your vet to discuss the other options, where you can both decide what is the next best thing for your pet to keep them happy and comfortable.

Mirtazapine Datasheet

All drugs have a manufacturer’s datasheet, which gives information about the drug’s use and possible side effects. Because Mirtazapine (generic) is a human drug, the datasheet isn’t as helpful. Instead, we’ve linked you to a vet version below.

Courses related to Mirtazapine

If your dog or cat is on Mirtazapine, you might be interested in learning more about their condition with our interactive, vet-written courses. Each one of our courses has been carefully written by qualified vets and e-learning specialists, and you have access to it – including all updates – for the rest of your pets’ life.

Please note that the information contained herein is provided for informational purposes only. Although it has been written by a vet, we cannot consider the individual nature of your pet’s problems so it does not constitute veterinary advice. If you have questions about your pet’s medication or their health you should contact a vet, who will be able to help.